/**
 * Semantic analysis for D types.
 *
 * Copyright:   Copyright (C) 1999-2025 by The D Language Foundation, All Rights Reserved
 * Authors:     $(LINK2 https://www.digitalmars.com, Walter Bright)
 * License:     $(LINK2 https://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
 * Source:      $(LINK2 https://github.com/dlang/dmd/blob/master/src/dmd/typesem.d, _typesem.d)
 * Documentation:  https://dlang.org/phobos/dmd_typesem.html
 * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/dmd/typesem.d
 */

module dmd.typesem;

import core.checkedint;
import core.stdc.string;
import core.stdc.stdio;

import dmd.access;
import dmd.aggregate;
import dmd.aliasthis;
import dmd.arrayop;
import dmd.arraytypes;
import dmd.astcodegen;
import dmd.astenums;
import dmd.dcast;
import dmd.dclass;
import dmd.declaration;
import dmd.denum;
import dmd.dimport;
import dmd.dinterpret;
import dmd.dmodule;
import dmd.dscope;
import dmd.dstruct;
import dmd.dsymbol;
import dmd.dsymbolsem;
import dmd.dtemplate;
import dmd.enumsem;
import dmd.errors;
import dmd.errorsink;
import dmd.expression;
import dmd.expressionsem;
import dmd.func;
import dmd.funcsem;
import dmd.globals;
import dmd.hdrgen;
import dmd.id;
import dmd.identifier;
import dmd.imphint;
import dmd.importc;
import dmd.init;
import dmd.initsem;
import dmd.location;
import dmd.visitor;
import dmd.mtype;
import dmd.mangle;
import dmd.nogc;
import dmd.objc;
import dmd.opover;
import dmd.optimize;
import dmd.parse;
import dmd.root.complex;
import dmd.root.ctfloat;
import dmd.root.rmem;
import dmd.common.outbuffer;
import dmd.rootobject;
import dmd.root.string;
import dmd.root.stringtable;
import dmd.safe;
import dmd.semantic3;
import dmd.sideeffect;
import dmd.target;
import dmd.tokens;

/*************************************
 * Resolve a tuple index, `s[oindex]`, by figuring out what `s[oindex]` represents.
 * Setting one of pe/pt/ps.
 * Params:
 *      loc = location for error messages
 *      sc = context
 *      s = symbol being indexed - could be a tuple, could be an expression
 *      pe = set if s[oindex] is an Expression, otherwise null
 *      pt = set if s[oindex] is a Type, otherwise null
 *      ps = set if s[oindex] is a Dsymbol, otherwise null
 *      oindex = index into s
 */
private void resolveTupleIndex(Loc loc, Scope* sc, Dsymbol s, out Expression pe, out Type pt, out Dsymbol ps, RootObject oindex)
{
    auto tup = s.isTupleDeclaration();

    auto eindex = isExpression(oindex);
    auto tindex = isType(oindex);
    auto sindex = isDsymbol(oindex);

    if (!tup)
    {
        // It's really an index expression
        if (tindex)
            eindex = new TypeExp(loc, tindex);
        else if (sindex)
            eindex = symbolToExp(sindex, loc, sc, false);
        Expression e = new IndexExp(loc, symbolToExp(s, loc, sc, false), eindex);
        e = e.expressionSemantic(sc);
        resolveExp(e, pt, pe, ps);
        return;
    }

    // Convert oindex to Expression, then try to resolve to constant.
    if (tindex)
        tindex.resolve(loc, sc, eindex, tindex, sindex);
    if (sindex)
        eindex = symbolToExp(sindex, loc, sc, false);
    if (!eindex)
    {
        .error(loc, "index `%s` is not an expression", oindex.toChars());
        pt = Type.terror;
        return;
    }

    eindex = semanticLength(sc, tup, eindex);
    eindex = eindex.ctfeInterpret();
    if (eindex.op == EXP.error)
    {
        pt = Type.terror;
        return;
    }
    const(uinteger_t) d = eindex.toUInteger();
    if (d >= tup.objects.length)
    {
        .error(loc, "sequence index `%llu` out of bounds `[0 .. %llu]`", d, cast(ulong)tup.objects.length);
        pt = Type.terror;
        return;
    }

    RootObject o = (*tup.objects)[cast(size_t)d];
    ps = isDsymbol(o);
    if (auto t = isType(o))
        pt = t.typeSemantic(loc, sc);
    if (auto e = isExpression(o))
        resolveExp(e, pt, pe, ps);
}

/*************************************
 * Takes an array of Identifiers and figures out if
 * it represents a Type, Expression, or Dsymbol.
 * Params:
 *      mt = array of identifiers
 *      loc = location for error messages
 *      sc = context
 *      s = symbol to start search at
 *      scopesym = unused
 *      pe = set if expression otherwise null
 *      pt = set if type otherwise null
 *      ps = set if symbol otherwise null
 *      typeid = set if in TypeidExpression https://dlang.org/spec/expression.html#TypeidExpression
 */
private void resolveHelper(TypeQualified mt, Loc loc, Scope* sc, Dsymbol s, Dsymbol scopesym,
    out Expression pe, out Type pt, out Dsymbol ps, bool intypeid = false)
{
    version (none)
    {
        printf("TypeQualified::resolveHelper(sc = %p, idents = '%s')\n", sc, mt.toChars());
        if (scopesym)
            printf("\tscopesym = '%s'\n", scopesym.toChars());
    }

    if (!s)
    {
        /* Look for what user might have intended
         */
        const p = mt.mutableOf().unSharedOf().toChars();
        auto id = Identifier.idPool(p[0 .. strlen(p)]);
        if (const n = importHint(id.toString()))
            error(loc, "`%s` is not defined, perhaps `import %.*s;` ?", p, cast(int)n.length, n.ptr);
        else if (auto s2 = sc.search_correct(id))
            error(loc, "undefined identifier `%s`, did you mean %s `%s`?", p, s2.kind(), s2.toChars());
        else if (const q = Scope.search_correct_C(id))
            error(loc, "undefined identifier `%s`, did you mean `%s`?", p, q);
        else if ((id == Id.This   && sc.getStructClassScope()) ||
                 (id == Id._super && sc.getClassScope()))
            error(loc, "undefined identifier `%s`, did you mean `typeof(%s)`?", p, p);
        else
            error(loc, "undefined identifier `%s`", p);

        pt = Type.terror;
        return;
    }

    //printf("\t1: s = '%s' %p, kind = '%s'\n",s.toChars(), s, s.kind());
    Declaration d = s.isDeclaration();
    if (d && (d.storage_class & STC.templateparameter))
        s = s.toAlias();
    else
    {
        // check for deprecated or disabled aliases
        // functions are checked after overloading
        // templates are checked after matching constraints
        if (!s.isFuncDeclaration() && !s.isTemplateDeclaration())
            s.checkDeprecated(loc, sc);
        if (d)
            d.checkDisabled(loc, sc, true);
    }
    s = s.toAlias();
    //printf("\t2: s = '%s' %p, kind = '%s'\n",s.toChars(), s, s.kind());
    for (size_t i = 0; i < mt.idents.length; i++)
    {
        RootObject id = mt.idents[i];
        switch (id.dyncast()) with (DYNCAST)
        {
        case expression:
        case type:
            Type tx;
            Expression ex;
            Dsymbol sx;
            resolveTupleIndex(loc, sc, s, ex, tx, sx, id);
            if (sx)
            {
                s = sx.toAlias();
                continue;
            }
            if (tx)
                ex = new TypeExp(loc, tx);
            assert(ex);

            ex = typeToExpressionHelper(mt, ex, i + 1);
            ex = ex.expressionSemantic(sc);
            resolveExp(ex, pt, pe, ps);
            return;
        default:
            break;
        }

        Type t = s.getType(); // type symbol, type alias, or type tuple?
        const errorsave = global.errors;
        SearchOptFlags flags = t is null ? SearchOpt.localsOnly : SearchOpt.ignorePrivateImports;

        Dsymbol sm = s.searchX(loc, sc, id, flags);
        if (sm)
        {
            if (!sc.ignoresymbolvisibility && !symbolIsVisible(sc, sm))
            {
                .error(loc, "`%s` is not visible from module `%s`", sm.toPrettyChars(), sc._module.toChars());
                sm = null;
            }
            // Same check as in dotIdSemanticProp(DotIdExp)
            else if (sm.isPackage() && checkAccess(sc, sm.isPackage()))
            {
                // @@@DEPRECATED_2.106@@@
                // Should be an error in 2.106. Just remove the deprecation call
                // and uncomment the null assignment
                deprecation(loc, "%s %s is not accessible here, perhaps add 'static import %s;'", sm.kind(), sm.toPrettyChars(), sm.toPrettyChars());
                //sm = null;
            }
        }
        if (global.errors != errorsave)
        {
            pt = Type.terror;
            return;
        }

        void helper3()
        {
            Expression e;
            VarDeclaration v = s.isVarDeclaration();
            FuncDeclaration f = s.isFuncDeclaration();
            if (intypeid || !v && !f)
                e = symbolToExp(s, loc, sc, true);
            else
                e = new VarExp(loc, s.isDeclaration(), true);

            e = typeToExpressionHelper(mt, e, i);
            e = e.expressionSemantic(sc);
            resolveExp(e, pt, pe, ps);
        }

        //printf("\t3: s = %p %s %s, sm = %p\n", s, s.kind(), s.toChars(), sm);
        if (intypeid && !t && sm && sm.needThis())
            return helper3();

        if (VarDeclaration v = s.isVarDeclaration())
        {
            // https://issues.dlang.org/show_bug.cgi?id=19913
            // v.type would be null if it is a forward referenced member.
            if (v.type is null)
                v.dsymbolSemantic(sc);
            if (v.storage_class & (STC.const_ | STC.immutable_ | STC.manifest) ||
                v.type.isConst() || v.type.isImmutable())
            {
                // https://issues.dlang.org/show_bug.cgi?id=13087
                // this.field is not constant always
                if (!v.isThisDeclaration())
                    return helper3();
            }
        }

        if (!sm)
            return helper3();

        if (sm.isAliasDeclaration)
            sm.checkDeprecated(loc, sc);
        s = sm.toAlias();
    }

    if (auto em = s.isEnumMember())
    {
        // It's not a type, it's an expression
        pe = em.getVarExp(loc, sc);
        return;
    }
    if (auto v = s.isVarDeclaration())
    {
        /* This is mostly same with DsymbolExp::semantic(), but we cannot use it
         * because some variables used in type context need to prevent lowering
         * to a literal or contextful expression. For example:
         *
         *  enum a = 1; alias b = a;
         *  template X(alias e){ alias v = e; }  alias x = X!(1);
         *  struct S { int v; alias w = v; }
         *      // TypeIdentifier 'a', 'e', and 'v' should be EXP.variable,
         *      // because getDsymbol() need to work in AliasDeclaration::semantic().
         */
        if (!v.type ||
            !v.type.deco && v.inuse)
        {
            if (v.inuse) // https://issues.dlang.org/show_bug.cgi?id=9494
                error(loc, "circular reference to %s `%s`", v.kind(), v.toPrettyChars());
            else
                error(loc, "forward reference to %s `%s`", v.kind(), v.toPrettyChars());
            pt = Type.terror;
            return;
        }
        if (v.type.ty == Terror)
            pt = Type.terror;
        else
            pe = new VarExp(loc, v);
        return;
    }
    if (auto fld = s.isFuncLiteralDeclaration())
    {
        //printf("'%s' is a function literal\n", fld.toChars());
        auto e = new FuncExp(loc, fld);
        pe = e.expressionSemantic(sc);
        return;
    }
    version (none)
    {
        if (FuncDeclaration fd = s.isFuncDeclaration())
        {
            pe = new DsymbolExp(loc, fd);
            return;
        }
    }

    Type t;
    while (1)
    {
        t = s.getType();
        if (t)
            break;
        ps = s;
        return;
    }

    if (auto ti = t.isTypeInstance())
        if (ti != mt && !ti.deco)
        {
            if (!ti.tempinst.errors)
                error(loc, "forward reference to `%s`", ti.toChars());
            pt = Type.terror;
            return;
        }

    if (t.ty == Ttuple)
        pt = t;
    else
        pt = t.merge();
}

/***************************************
 * Search for identifier id as a member of `this`.
 * `id` may be a template instance.
 *
 * Params:
 *  loc = location to print the error messages
 *  sc = the scope where the symbol is located
 *  id = the id of the symbol
 *  flags = the search flags which can be `SearchLocalsOnly` or `SearchOpt.ignorePrivateImports`
 *
 * Returns:
 *      symbol found, NULL if not
 */
private Dsymbol searchX(Dsymbol dsym, Loc loc, Scope* sc, RootObject id, SearchOptFlags flags)
{
    //printf("Dsymbol::searchX(this=%p,%s, ident='%s')\n", this, toChars(), ident.toChars());
    Dsymbol s = dsym.toAlias();
    Dsymbol sm;
    if (Declaration d = s.isDeclaration())
    {
        if (d.inuse)
        {
            .error(loc, "circular reference to `%s`", d.toPrettyChars());
            return null;
        }
    }
    switch (id.dyncast())
    {
    case DYNCAST.identifier:
        sm = s.search(loc, cast(Identifier)id, flags);
        break;
    case DYNCAST.dsymbol:
        {
            // It's a template instance
            //printf("\ttemplate instance id\n");
            Dsymbol st = cast(Dsymbol)id;
            TemplateInstance ti = st.isTemplateInstance();
            sm = s.search(loc, ti.name);
            if (!sm)
                return null;
            sm = sm.toAlias();
            TemplateDeclaration td = sm.isTemplateDeclaration();
            if (!td)
                return null; // error but handled later
            ti.tempdecl = td;
            if (!ti.semanticRun)
                ti.dsymbolSemantic(sc);
            sm = ti.toAlias();
            break;
        }
    case DYNCAST.type:
    case DYNCAST.expression:
    default:
        assert(0);
    }
    return sm;
}

/***************************************************
 * Determine if type t is copyable.
 * Params:
 *      t = type to check
 * Returns:
 *      true if we can copy it
 */
bool isCopyable(Type t)
{
    //printf("isCopyable() %s\n", t.toChars());
    if (auto ts = t.isTypeStruct())
    {
        if (ts.sym.postblit &&
            ts.sym.postblit.storage_class & STC.disable)
            return false;
        if (ts.sym.hasCopyCtor)
        {
            // check if there is a matching overload of the copy constructor and whether it is disabled or not
            // `assert(ctor)` fails on Win32 and Win_32_64. See: https://auto-tester.puremagic.com/pull-history.ghtml?projectid=1&repoid=1&pullid=10575
            Dsymbol ctor = search_function(ts.sym, Id.ctor);
            assert(ctor);
            scope el = new IdentifierExp(Loc.initial, Id.p); // dummy lvalue
            el.type = cast() ts;
            Expressions* args = new Expressions();
            args.push(el);
            FuncDeclaration f = resolveFuncCall(Loc.initial, null, ctor, null, cast()ts, ArgumentList(args), FuncResolveFlag.quiet);
            if (!f || f.storage_class & STC.disable)
                return false;
        }
    }
    return true;
}

/************************************
 * Determine mutability of indirections in (ref) t.
 *
 * Returns: When the type has any mutable indirections, returns 0.
 * When all indirections are immutable, returns 2.
 * Otherwise, when the type has const/inout indirections, returns 1.
 *
 * Params:
 *      isRef = if true, check `ref t`; otherwise, check just `t`
 *      t = the type that is being checked
 */
int mutabilityOfType(bool isRef, Type t)
{
    if (isRef)
    {
        if (t.mod & MODFlags.immutable_)
            return 2;
        if (t.mod & (MODFlags.const_ | MODFlags.wild))
            return 1;
        return 0;
    }

    t = t.baseElemOf();

    if (!t.hasPointers() || t.mod & MODFlags.immutable_)
        return 2;

    /* Accept immutable(T)[] and immutable(T)* as being strongly pure
     */
    if (t.ty == Tarray || t.ty == Tpointer)
    {
        Type tn = t.nextOf().toBasetype();
        if (tn.mod & MODFlags.immutable_)
            return 2;
        if (tn.mod & (MODFlags.const_ | MODFlags.wild))
            return 1;
    }

    /* The rest of this is too strict; fix later.
     * For example, the only pointer members of a struct may be immutable,
     * which would maintain strong purity.
     * (Just like for dynamic arrays and pointers above.)
     */
    if (t.mod & (MODFlags.const_ | MODFlags.wild))
        return 1;

    /* Should catch delegates and function pointers, and fold in their purity
     */
    return 0;
}

/********************************************
 * Set 'purity' field of 'typeFunction'.
 * Do this lazily, as the parameter types might be forward referenced.
 */
void purityLevel(TypeFunction typeFunction)
{
    TypeFunction tf = typeFunction;
    if (tf.purity != PURE.fwdref)
        return;

    typeFunction.purity = PURE.const_; // assume strong until something weakens it

    /* Evaluate what kind of purity based on the modifiers for the parameters
     */
    foreach (i, fparam; tf.parameterList)
    {
        Type t = fparam.type;
        if (!t)
            continue;

        if (fparam.storageClass & (STC.lazy_ | STC.out_))
        {
            typeFunction.purity = PURE.weak;
            break;
        }
        const pref = (fparam.storageClass & STC.ref_) != 0;
        if (mutabilityOfType(pref, t) == 0)
            typeFunction.purity = PURE.weak;
    }

    tf.purity = typeFunction.purity;
}

/******************************************
 * We've mistakenly parsed `t` as a type.
 * Redo `t` as an Expression only if there are no type modifiers.
 * Params:
 *      t = mistaken type
 * Returns:
 *      t redone as Expression, null if cannot
 */
Expression typeToExpression(Type t)
{
    static Expression visitSArray(TypeSArray t)
    {
        if (auto e = t.next.typeToExpression())
            return new ArrayExp(t.dim.loc, e, t.dim);
        return null;
    }

    static Expression visitAArray(TypeAArray t)
    {
        if (auto e = t.next.typeToExpression())
        {
            if (auto ei = t.index.typeToExpression())
                return new ArrayExp(t.loc, e, ei);
        }
        return null;
    }

    static Expression visitIdentifier(TypeIdentifier t)
    {
        return typeToExpressionHelper(t, new IdentifierExp(t.loc, t.ident));
    }

    static Expression visitInstance(TypeInstance t)
    {
        return typeToExpressionHelper(t, new ScopeExp(t.loc, t.tempinst));
    }

    // easy way to enable 'auto v = new int[mixin("exp")];' in 2.088+
    static Expression visitMixin(TypeMixin t)
    {
        return new TypeExp(t.loc, t);
    }

    if (t.mod)
        return null;
    switch (t.ty)
    {
        case Tsarray:   return visitSArray(t.isTypeSArray());
        case Taarray:   return visitAArray(t.isTypeAArray());
        case Tident:    return visitIdentifier(t.isTypeIdentifier());
        case Tinstance: return visitInstance(t.isTypeInstance());
        case Tmixin:    return visitMixin(t.isTypeMixin());
        default:        return null;
    }
}

/*************************************
 * https://issues.dlang.org/show_bug.cgi?id=14488
 * Check if the inner most base type is complex or imaginary.
 * Should only give alerts when set to emit transitional messages.
 * Params:
 *  type = type to check
 *  loc = The source location.
 *  sc = scope of the type
 */
extern (D) bool checkComplexTransition(Type type, Loc loc, Scope* sc)
{
    if (sc.isDeprecated())
        return false;
    // Don't complain if we're inside a template constraint
    // https://issues.dlang.org/show_bug.cgi?id=21831
    if (sc.inTemplateConstraint)
        return false;

    Type t = type.baseElemOf();
    while (t.ty == Tpointer || t.ty == Tarray)
        t = t.nextOf().baseElemOf();

    // Basetype is an opaque enum, nothing to check.
    if (t.ty == Tenum && !(cast(TypeEnum)t).sym.memtype)
        return false;

    if (t.isImaginary() || t.isComplex())
    {
        if (sc.inCfile)
            return true;            // complex/imaginary not deprecated in C code
        Type rt;
        switch (t.ty)
        {
        case Tcomplex32:
        case Timaginary32:
            rt = Type.tfloat32;
            break;

        case Tcomplex64:
        case Timaginary64:
            rt = Type.tfloat64;
            break;

        case Tcomplex80:
        case Timaginary80:
            rt = Type.tfloat80;
            break;

        default:
            assert(0);
        }
        // @@@DEPRECATED_2.117@@@
        // Deprecated in 2.097 - Can be made an error from 2.117.
        // The deprecation period is longer than usual as `cfloat`,
        // `cdouble`, and `creal` were quite widely used.
        if (t.isComplex())
        {
            deprecation(loc, "use of complex type `%s` is deprecated, use `std.complex.Complex!(%s)` instead",
                type.toChars(), rt.toChars());
            return true;
        }
        else
        {
            deprecation(loc, "use of imaginary type `%s` is deprecated, use `%s` instead",
                type.toChars(), rt.toChars());
            return true;
        }
    }
    return false;
}

/********************************
 * 'args' are being matched to function type 'tf'
 * Determine match level.
 * Params:
 *      fd = function being called, if a symbol
 *      tf = function type
 *      tthis = type of `this` pointer, null if not member function
 *      argumentList = arguments to function call
 *      flag = 1: performing a partial ordering match
 *      errorHelper = delegate to call for error messages
 *      sc = context
 * Returns:
 *      MATCHxxxx
 */
extern (D) MATCH callMatch(FuncDeclaration fd, TypeFunction tf, Type tthis, ArgumentList argumentList,
        int flag = 0, void delegate(const(char)*) scope errorHelper = null, Scope* sc = null)
{
    //printf("callMatch() fd: %s, tf: %s\n", fd ? fd.ident.toChars() : "null", toChars(tf));
    MATCH match = MATCH.exact; // assume exact match
    ubyte wildmatch = 0;

    if (tthis)
    {
        Type t = tthis;
        if (t.toBasetype().ty == Tpointer)
            t = t.toBasetype().nextOf(); // change struct* to struct
        if (t.mod != tf.mod)
        {
            if (MODimplicitConv(t.mod, tf.mod))
                match = MATCH.constant;
            else if ((tf.mod & MODFlags.wild) && MODimplicitConv(t.mod, (tf.mod & ~MODFlags.wild) | MODFlags.const_))
            {
                match = MATCH.constant;
            }
            else
                return MATCH.nomatch;
        }
        if (tf.isWild())
        {
            if (t.isWild())
                wildmatch |= MODFlags.wild;
            else if (t.isConst())
                wildmatch |= MODFlags.const_;
            else if (t.isImmutable())
                wildmatch |= MODFlags.immutable_;
            else
                wildmatch |= MODFlags.mutable;
        }
    }

    ParameterList* parameterList = &tf.parameterList;
    const nparams = parameterList.length;
    if (argumentList.length > nparams)
    {
        if (parameterList.varargs == VarArg.none)
        {
            // suppress early exit if an error message is wanted,
            // so we can check any matching args are valid
            if (!errorHelper)
                return MATCH.nomatch;
        }
        // too many args; no match
        match = MATCH.convert; // match ... with a "conversion" match level
    }

    // https://issues.dlang.org/show_bug.cgi?id=22997
    if (parameterList.varargs == VarArg.none && nparams > argumentList.length && !parameterList.hasDefaultArgs)
    {
        if (errorHelper)
        {
            OutBuffer buf;
            buf.printf("too few arguments, expected %d, got %d", cast(int)nparams, cast(int)argumentList.length);
            errorHelper(buf.peekChars());
        }
        return MATCH.nomatch;
    }
    const(char)* failMessage;
    const(char)** pMessage = errorHelper ? &failMessage : null;
    OutBuffer buf;
    auto resolvedArgs = tf.resolveNamedArgs(argumentList, errorHelper ? &buf : null);
    Expression[] args;
    if (!resolvedArgs)
    {
        if (buf.length)
        {
            errorHelper(buf.peekChars());
            return MATCH.nomatch;
        }

        // if no message was provided, it was because of overflow which will be diagnosed below
        match = MATCH.nomatch;
        args = argumentList.arguments ? (*argumentList.arguments)[] : null;
    }
    else
    {
        args = (*resolvedArgs)[];
    }

    foreach (u, p; *parameterList)
    {
        if (u >= args.length)
            break;

        Expression arg = args[u];
        if (!arg)
            continue; // default argument

        Type tprm = p.type;
        Type targ = arg.type;

        if (!(p.isLazy() && tprm.ty == Tvoid && targ.ty != Tvoid))
        {
            const isRef = p.isReference();
            wildmatch |= targ.deduceWild(tprm, isRef);
        }
    }
    if (wildmatch)
    {
        /* Calculate wild matching modifier
         */
        if (wildmatch & MODFlags.const_ || wildmatch & (wildmatch - 1))
            wildmatch = MODFlags.const_;
        else if (wildmatch & MODFlags.immutable_)
            wildmatch = MODFlags.immutable_;
        else if (wildmatch & MODFlags.wild)
            wildmatch = MODFlags.wild;
        else
        {
            assert(wildmatch & MODFlags.mutable);
            wildmatch = MODFlags.mutable;
        }
    }

    foreach (u, p; *parameterList)
    {
        MATCH m;

        assert(p);

        // One or more arguments remain
        if (u < args.length)
        {
            Expression arg = args[u];
            if (!arg)
                continue; // default argument
            m = argumentMatchParameter(fd, tf, p, arg, wildmatch, flag, sc, pMessage);
            if (failMessage)
            {
                buf.reset();
                buf.writestring(failMessage);
            }
        }
        else if (p.defaultArg)
            continue;

        /* prefer matching the element type rather than the array
         * type when more arguments are present with T[]...
         */
        if (parameterList.varargs == VarArg.typesafe && u + 1 == nparams && args.length > nparams)
            goto L1;

        //printf("\tm = %d\n", m);
        if (m == MATCH.nomatch) // if no match
        {
        L1:
            if (parameterList.varargs == VarArg.typesafe && u + 1 == nparams) // if last varargs param
            {
                Expression[] trailingArgs;
                if (args.length >= u)
                    trailingArgs = args[u .. $];
                if (auto vmatch = matchTypeSafeVarArgs(tf, p, trailingArgs, pMessage))
                    return vmatch < match ? vmatch : match;
                // Error message was already generated in `matchTypeSafeVarArgs`
                if (failMessage)
                    errorHelper(failMessage);
                return MATCH.nomatch;
            }
            if (errorHelper)
            {
                if (u >= args.length)
                    TypeFunction.getMatchError(buf, "missing argument for parameter #%d: `%s`",
                        u + 1, parameterToChars(p, tf, false));
                // If an error happened previously, `pMessage` was already filled
                else if (buf.length == 0)
                    buf.writestring(tf.getParamError(args[u], p));

                errorHelper(buf.peekChars());
            }
            return MATCH.nomatch;
        }
        if (m < match)
            match = m; // pick worst match
    }

    if (errorHelper && !parameterList.varargs && args.length > nparams)
    {
        // all parameters had a match, but there are surplus args
        OutBuffer buf2;
        TypeFunction.getMatchError(buf2, "expected %d argument(s), not %d", nparams, args.length);
        errorHelper(buf2.extractChars());
        return MATCH.nomatch;
    }
    //printf("match = %d\n", match);
    return match;
}

/**
 * Used by `callMatch` to check if the copy constructor may be called to
 * copy the argument
 *
 * This is done by seeing if a call to the copy constructor can be made:
 * ```
 * typeof(tprm) __copytemp;
 * copytemp.__copyCtor(arg);
 * ```
 */
private extern(D) bool isCopyConstructorCallable (StructDeclaration argStruct,
    Expression arg, Type tprm, Scope* sc, const(char)** pMessage)
{
    //printf("isCopyConstructorCallable() argStruct: %s arg: %s tprm: %s\n", argStruct.toChars(), toChars(arg), toChars(tprm));
    auto tmp = new VarDeclaration(arg.loc, tprm, Identifier.generateId("__copytemp"), null);
    tmp.storage_class = STC.rvalue | STC.temp | STC.ctfe;
    tmp.dsymbolSemantic(sc);
    Expression ve = new VarExp(arg.loc, tmp);
    Expression e = new DotIdExp(arg.loc, ve, Id.ctor);
    e = new CallExp(arg.loc, e, arg);
    //printf("e = %s\n", e.toChars());
    if (dmd.expressionsem.trySemantic(e, sc))
        return true;

    if (!pMessage)
        return false;

    /* https://issues.dlang.org/show_bug.cgi?id=22202
     *
     * If a function was deduced by semantic on the CallExp,
     * it means that resolveFuncCall completed succesfully.
     * Therefore, there exists a callable copy constructor,
     * however, it cannot be called because scope constraints
     * such as purity, safety or nogc.
     */
    OutBuffer buf;
    auto callExp = e.isCallExp();

    bool nocpctor()
    {
        buf.printf("`struct %s` does not define a copy constructor for `%s` to `%s` copies",
                   argStruct.toChars(), arg.type.toChars(), tprm.toChars());
        *pMessage = buf.extractChars();
        return false;
    }

    auto f = callExp.f;
    if (!f)
        return nocpctor();

    if (f.isDisabled() && !f.isGenerated())
    {
        /* https://issues.dlang.org/show_bug.cgi?id=24301
         * Copy constructor is explicitly disabled
         */
        buf.printf("`%s` copy constructor cannot be used because it is annotated with `@disable`",
            f.type.toChars());
        *pMessage = buf.extractChars();
        return false;
    }

    bool bpure = !f.isPure && sc.func.setImpure(arg.loc, null);
    bool bsafe = !f.isSafe() && !f.isTrusted() && sc.setUnsafe(false, arg.loc, null);
    bool bnogc = !f.isNogc && sc.func.setGC(arg.loc, null);
    if (bpure | bsafe | bnogc)
    {
        const nullptr = "".ptr;
        buf.printf("`%s` copy constructor cannot be called from a `%s%s%s` context",
            f.type.toChars(),
            bpure ? "pure " .ptr : nullptr,
            bsafe ? "@safe ".ptr : nullptr,
            bnogc ? "nogc"  .ptr : nullptr);
    }
    else if (f.isGenerated() && f.isDisabled())
    {
        /* https://issues.dlang.org/show_bug.cgi?id=23097
         * Compiler generated copy constructor failed.
         */
        buf.printf("generating a copy constructor for `struct %s` failed, therefore instances of it are uncopyable",
                   argStruct.toChars());
    }
    else
    {
        /* Although a copy constructor may exist, no suitable match was found.
         * i.e: `inout` constructor creates `const` object, not mutable.
         * Fallback to using the original generic error before https://issues.dlang.org/show_bug.cgi?id=22202.
         */
        return nocpctor();
    }

    *pMessage = buf.extractChars();

    return false;
}

/**
 * Match a single parameter to an argument.
 *
 * This function is called by `TypeFunction.callMatch` while iterating over
 * the list of parameter. Here we check if `arg` is a match for `p`,
 * which is mostly about checking if `arg.type` converts to type of `p`
 * and some check about value reference.
 *
 * Params:
 *   fd = the function being called if symbol, null if not
 *   tf = The `TypeFunction`, only used for error reporting
 *   p = The parameter of `tf` being matched
 *   arg = Argument being passed (bound) to `p`
 *   wildmatch = Wild (`inout`) matching level, derived from the full argument list
 *   flag = A non-zero value means we are doing a partial ordering check
 *          (no value semantic check)
 *   sc = Scope we are in
 *   pMessage = A buffer to write the error in, or `null`
 *
 * Returns: Whether `trailingArgs` match `p`.
 */
private extern(D) MATCH argumentMatchParameter (FuncDeclaration fd, TypeFunction tf, Parameter p,
    Expression arg, ubyte wildmatch, int flag, Scope* sc, const(char)** pMessage)
{
    static if (0)
    printf("argumentMatchParameter() sc: %p, fd: %s, tf: %s, p: %s, arg: %s, arg.type: %s\n",
        sc, fd ? fd.ident.toChars() : "null", tf.toChars(), parameterToChars(p, tf, false), arg.toChars(), arg.type.toChars());
    MATCH m;
    Type targ = arg.type;
    Type tprm = wildmatch ? p.type.substWildTo(wildmatch) : p.type;

    if (p.isLazy() && tprm.ty == Tvoid && targ.ty != Tvoid)
        m = MATCH.convert;
    else if (flag)
    {
        // for partial ordering, value is an irrelevant mockup, just look at the type
        m = targ.implicitConvTo(tprm);
    }
    else
    {
        const isRef = p.isReference();

        StructDeclaration argStruct, prmStruct;
        if (targ.ty == Tstruct && tprm.ty == Tstruct)
        {
            // if the argument and the parameter are of the same unqualified struct type
            argStruct = (cast(TypeStruct)targ).sym;
            prmStruct = (cast(TypeStruct)tprm).sym;

            /* if both a copy constructor and move constructor exist, then match
             * the lvalue to the copy constructor only and the rvalue to the move constructor
             * only
             */
            if (argStruct == prmStruct && fd)
            {
                if (auto cfd = fd.isCtorDeclaration())
                {
                    /* Get struct that constructor is making
                     */

                    auto t1 = cfd.type.toBasetype();
                    auto t2 = t1.nextOf();
                    auto t3 = t2.isTypeStruct();
                    if (t3)
                    {
                    auto ctorStruct = t3.sym;
//                    StructDeclaration ctorStruct = cfd.type.toBasetype().nextOf().isTypeStruct().sym;

                    if (prmStruct == ctorStruct && ctorStruct.hasCopyCtor && ctorStruct.hasMoveCtor)
                    {
                        if (cfd.isCpCtor && !arg.isLvalue())
                            return MATCH.nomatch;       // copy constructor is only for lvalues
                        if (cfd.isMoveCtor && arg.isLvalue())
                            return MATCH.nomatch;       // move constructor is only for rvalues
                    }
                    }
                }
            }
        }

        // check if the copy constructor may be called to copy the argument
        if (arg.isLvalue() && !isRef && argStruct && argStruct == prmStruct && argStruct.hasCopyCtor)
        {
            if (!isCopyConstructorCallable(argStruct, arg, tprm, sc, pMessage))
                return MATCH.nomatch;
            m = MATCH.exact;
        }
        else
        {
            import dmd.dcast : cimplicitConvTo;
            m = (sc && sc.inCfile) ? arg.cimplicitConvTo(tprm) : arg.implicitConvTo(tprm);
        }
    }

    // Non-lvalues do not match ref or out parameters
    if (!p.isReference())
        return m;

    // https://issues.dlang.org/show_bug.cgi?id=13783
    // Don't use toBasetype() to handle enum types.
    Type ta = targ;
    Type tp = tprm;
    //printf("fparam[%d] ta = %s, tp = %s\n", u, ta.toChars(), tp.toChars());

    if (m && !arg.isLvalue())
    {
        if (p.storageClass & STC.out_)
        {
            if (pMessage) *pMessage = tf.getParamError(arg, p);
            return MATCH.nomatch;
        }

        if (arg.op == EXP.string_ && tp.ty == Tsarray)
        {
            if (ta.ty != Tsarray)
            {
                Type tn = tp.nextOf().castMod(ta.nextOf().mod);
                dinteger_t dim = (cast(StringExp)arg).len;
                ta = tn.sarrayOf(dim);
            }
        }
        else if (arg.op == EXP.slice && tp.ty == Tsarray)
        {
            // Allow conversion from T[lwr .. upr] to ref T[upr-lwr]
            if (ta.ty != Tsarray)
            {
                Type tn = ta.nextOf();
                dinteger_t dim = (cast(TypeSArray)tp).dim.toUInteger();
                ta = tn.sarrayOf(dim);
            }
        }
        else if (p.storageClass & STC.constscoperef)
        {
            // Allow converting a literal to an `in` which is `ref`
            if (arg.op == EXP.arrayLiteral && tp.ty == Tsarray)
            {
                Type tn = tp.nextOf();
                dinteger_t dim = (cast(TypeSArray)tp).dim.toUInteger();
                ta = tn.sarrayOf(dim);
            }

            // Need to make this a rvalue through a temporary
            m = MATCH.convert;
        }
        else if (!(sc && sc.previews.rvalueRefParam) ||
                 p.storageClass & STC.out_ ||
                 !arg.type.isCopyable())  // can't copy to temp for ref parameter
        {
            if (pMessage) *pMessage = tf.getParamError(arg, p);
            return MATCH.nomatch;
        }
        else
        {
            /* in functionParameters() we'll convert this
             * rvalue into a temporary
             */
            m = MATCH.convert;
        }
    }

    /* If the match is not already perfect or if the arg
       is not a lvalue then try the `alias this` chain
       see  https://issues.dlang.org/show_bug.cgi?id=15674
       and https://issues.dlang.org/show_bug.cgi?id=21905
    */
    if (ta != tp || !arg.isLvalue())
    {
        Type firsttab = ta.toBasetype();
        while (1)
        {
            Type tab = ta.toBasetype();
            Type tat = tab.aliasthisOf();
            if (!tat || !tat.implicitConvTo(tprm))
                break;
            if (tat == tab || tat == firsttab)
                break;
            ta = tat;
        }
    }

    /* A ref variable should work like a head-const reference.
     * e.g. disallows:
     *  ref T      <- an lvalue of const(T) argument
     *  ref T[dim] <- an lvalue of const(T[dim]) argument
     */
    if (!ta.constConv(tp))
    {
        if (pMessage) *pMessage = tf.getParamError(arg, p);
        return MATCH.nomatch;
    }

    return m;
}

// arguments get specially formatted
private const(char)* getParamError(TypeFunction tf, Expression arg, Parameter par)
{
    if (global.gag && !global.params.v.showGaggedErrors)
        return null;
    // show qualification when toChars() is the same but types are different
    // https://issues.dlang.org/show_bug.cgi?id=19948
    // when comparing the type with strcmp, we need to drop the qualifier
    bool qual = !arg.type.mutableOf().equals(par.type.mutableOf()) &&
        strcmp(arg.type.mutableOf().toChars(), par.type.mutableOf().toChars()) == 0;
    auto at = qual ? arg.type.toPrettyChars(true) : arg.type.toChars();
    OutBuffer buf;
    // only mention rvalue if it's relevant
    const rv = !arg.isLvalue() && par.isReference();
    buf.printf("cannot pass %sargument `%s` of type `%s` to parameter `%s`",
        rv ? "rvalue ".ptr : "".ptr, arg.toErrMsg(), at,
        parameterToChars(par, tf, qual));
    return buf.extractChars();
}

/**
 * Match the remaining arguments `trailingArgs` with parameter `p`.
 *
 * Assume we already checked that `p` is the last parameter of `tf`,
 * and we want to know whether the arguments would match `p`.
 *
 * Params:
 *   tf = The `TypeFunction`, only used for error reporting
 *   p = The last parameter of `tf` which is variadic
 *   trailingArgs = The remaining arguments that should match `p`
 *   pMessage = A buffer to write the error in, or `null`
 *
 * Returns: Whether `trailingArgs` match `p`.
 */
private extern(D) MATCH matchTypeSafeVarArgs(TypeFunction tf, Parameter p,
    Expression[] trailingArgs, const(char)** pMessage)
{
    Type tb = p.type.toBasetype();

    switch (tb.ty)
    {
    case Tsarray:
        TypeSArray tsa = cast(TypeSArray)tb;
        dinteger_t sz = tsa.dim.toInteger();
        if (sz != trailingArgs.length)
        {
            if (pMessage)
            {
                OutBuffer buf;
                TypeFunction.getMatchError(buf, "expected %llu variadic argument(s), not %zu",
                    sz, trailingArgs.length);
                *pMessage = buf.extractChars();
            }
            return MATCH.nomatch;
        }
        goto case Tarray;
    case Tarray:
    {
        MATCH match = MATCH.exact;
        TypeArray ta = cast(TypeArray)tb;
        foreach (arg; trailingArgs)
        {
            MATCH m;
            assert(arg);

            /* If lazy array of delegates,
             * convert arg(s) to delegate(s)
             */
            Type tret = p.isLazyArray();
            if (tret)
            {
                if (ta.next.equals(arg.type))
                    m = MATCH.exact;
                else if (tret.toBasetype().ty == Tvoid)
                    m = MATCH.convert;
                else
                {
                    m = arg.implicitConvTo(tret);
                    if (m == MATCH.nomatch)
                        m = arg.implicitConvTo(ta.next);
                }
            }
            else
                m = arg.implicitConvTo(ta.next);

            if (m == MATCH.nomatch)
            {
                if (pMessage) *pMessage = tf.getParamError(arg, p);
                return MATCH.nomatch;
            }
            if (m < match)
                match = m;
        }
        return match;
    }
    case Tclass:
        // We leave it up to the actual constructor call to do the matching.
        return MATCH.exact;

    default:
        // We can have things as `foo(int[int] wat...)` but they only match
        // with an associative array proper.
        if (pMessage && trailingArgs.length) *pMessage = tf.getParamError(trailingArgs[0], p);
        return MATCH.nomatch;
    }
}

/***************************************
 * Return !=0 if type has pointers that need to
 * be scanned by the GC during a collection cycle.
 */
bool hasPointers(Type t)
{
    bool visitType(Type _)              { return false; }
    bool visitDArray(TypeDArray _)      { return true; }
    bool visitAArray(TypeAArray _)      { return true; }
    bool visitPointer(TypePointer _)    { return true; }
    bool visitDelegate(TypeDelegate _)  { return true; }
    bool visitClass(TypeClass _)        { return true; }
    bool visitEnum(TypeEnum t)          { return t.memType().hasPointers(); }

    /* Although null isn't dereferencable, treat it as a pointer type for
     * attribute inference, generic code, etc.
     */
    bool visitNull(TypeNull _)          { return true; }

    bool visitSArray(TypeSArray t)
    {
        /* Don't want to do this, because:
         *    struct S { T* array[0]; }
         * may be a variable length struct.
         */
        //if (dim.toInteger() == 0)
        //    return false;

        if (t.next.ty == Tvoid)
        {
            // Arrays of void contain arbitrary data, which may include pointers
            return true;
        }
        else
            return t.next.hasPointers();
    }

    bool visitStruct(TypeStruct t)
    {
        StructDeclaration sym = t.sym;

        if (sym.members && !sym.determineFields() && sym.type != Type.terror)
            error(sym.loc, "no size because of forward references");

        sym.determineTypeProperties();
        return sym.hasPointerField;
    }


    switch(t.ty)
    {
        default:            return visitType(t);
        case Tsarray:       return visitSArray(t.isTypeSArray());
        case Tarray:        return visitDArray(t.isTypeDArray());
        case Taarray:       return visitAArray(t.isTypeAArray());
        case Tpointer:      return visitPointer(t.isTypePointer());
        case Tdelegate:     return visitDelegate(t.isTypeDelegate());
        case Tstruct:       return visitStruct(t.isTypeStruct());
        case Tenum:         return visitEnum(t.isTypeEnum());
        case Tclass:        return visitClass(t.isTypeClass());
        case Tnull:         return visitNull(t.isTypeNull());
    }
}

/**************************************
 * Returns an indirect type one step from t.
 */
Type getIndirection(Type t)
{
    t = t.baseElemOf();
    if (t.ty == Tarray || t.ty == Tpointer)
        return t.nextOf().toBasetype();
    if (t.ty == Taarray || t.ty == Tclass)
        return t;
    if (t.ty == Tstruct)
        return t.hasPointers() ? t : null; // TODO

    // should consider TypeDelegate?
    return null;
}

uinteger_t size(Type t)
{
    return size(t, Loc.initial);
}

uinteger_t size(Type t, Loc loc)
{

    uinteger_t visitType(Type t)
    {
        error(loc, "no size for type `%s`", t.toChars());
        return SIZE_INVALID;
    }

    uinteger_t visitBasic(TypeBasic t)
    {
        uint size;
        //printf("TypeBasic::size()\n");
        switch (t.ty)
        {
            case Tint8:
            case Tuns8:
                size = 1;
                break;

            case Tint16:
            case Tuns16:
                size = 2;
                break;

            case Tint32:
            case Tuns32:
            case Tfloat32:
            case Timaginary32:
                size = 4;
                break;

            case Tint64:
            case Tuns64:
            case Tfloat64:
            case Timaginary64:
                size = 8;
                break;

            case Tfloat80:
            case Timaginary80:
                size = target.realsize;
                break;

            case Tcomplex32:
                size = 8;
                break;

            case Tcomplex64:
            case Tint128:
            case Tuns128:
                size = 16;
                break;

            case Tcomplex80:
                size = target.realsize * 2;
                break;

            case Tvoid:
                //size = Type::size();      // error message
                size = 1;
                break;

            case Tbool:
                size = 1;
                break;

            case Tchar:
                size = 1;
                break;

            case Twchar:
                size = 2;
                break;

            case Tdchar:
                size = 4;
                break;

            default:
                assert(0);
            }

        //printf("TypeBasic::size() = %d\n", size);
        return size;
    }

    uinteger_t visitSArray(TypeSArray t)
    {
        //printf("TypeSArray::size()\n");
        const n = t.numberOfElems(loc);
        const elemsize = t.baseElemOf().size(loc);
        bool overflow = false;
        const sz = mulu(n, elemsize, overflow);
        if (overflow || sz >= uint.max)
        {
            if (elemsize != SIZE_INVALID && n != uint.max)
                error(loc, "static array `%s` size overflowed to %lld", t.toChars(), cast(long)sz);
            return SIZE_INVALID;
        }
        return sz;

    }

    uinteger_t visitTypeQualified(TypeQualified t)
    {
        if (t.ty == Ttypeof)
        {
            auto type = (cast(TypeTypeof)t).exp.type;
            if (type)
                return type.size(loc);
        }

        error(t.loc, "size of type `%s` is not known", t.toChars());
        return SIZE_INVALID;
    }

    switch(t.ty)
    {
        default:            return t.isTypeBasic() ? visitBasic(t.isTypeBasic()) : visitType(t);
        case Ttraits:
        case Terror:        return SIZE_INVALID;
        case Tvector:       return t.isTypeVector().basetype.size();
        case Tsarray:       return visitSArray(t.isTypeSArray());
        case Tdelegate:
        case Tarray:        return target.ptrsize * 2;
        case Tpointer:
        case Treference:
        case Tclass:
        case Taarray:       return target.ptrsize;
        case Tident:
        case Tinstance:
        case Ttypeof:
        case Treturn:       return visitTypeQualified(cast(TypeQualified)t);
        case Tstruct:       return t.isTypeStruct().sym.size(loc);
        case Tenum:         return t.isTypeEnum().sym.getMemtype(loc).size(loc);
        case Tnull:         return t.tvoidptr.size(loc);
        case Tnoreturn:     return 0;
    }
}

/*******************************
 * Determine if converting 'this' to 'to' is an identity operation,
 * a conversion to const operation, or the types aren't the same.
 * Returns:
 *      MATCH.exact      'this' == 'to'
 *      MATCH.constant      'to' is const
 *      MATCH.nomatch    conversion to mutable or invariant
 */
MATCH constConv(Type from, Type to)
{
    MATCH visitType(Type from)
    {
        //printf("Type::constConv(this = %s, to = %s)\n", from.toChars(), to.toChars());
        if (from.equals(to))
            return MATCH.exact;
        if (from.ty == to.ty && MODimplicitConv(from.mod, to.mod))
            return MATCH.constant;
        return MATCH.nomatch;
    }

    MATCH visitNext(TypeNext from)
    {
        //printf("TypeNext::constConv from = %s, to = %s\n", from.toChars(), to.toChars());
        if (from.equals(to))
            return MATCH.exact;

        if (!(from.ty == to.ty && MODimplicitConv(from.mod, to.mod)))
            return MATCH.nomatch;

        Type tn = to.nextOf();
        if (!(tn && from.next.ty == tn.ty))
            return MATCH.nomatch;

        MATCH m;
        if (to.isConst()) // whole tail const conversion
        {
            // Recursive shared level check
            m = from.next.constConv(tn);
            if (m == MATCH.exact)
                m = MATCH.constant;
        }
        else
        {
            //printf("\tnext => %s, to.next => %s\n", from.next.toChars(), tn.toChars());
            m = from.next.equals(tn) ? MATCH.constant : MATCH.nomatch;
        }
        return m;
    }

    MATCH visitSArray(TypeSArray from)
    {
        if (auto tsa = to.isTypeSArray())
        {
            if (!from.dim.equals(tsa.dim))
                return MATCH.nomatch;
        }
        return visitNext(from);
    }

    MATCH visitAArray(TypeAArray from)
    {
        if (auto taa = to.isTypeAArray())
        {
            MATCH mindex = from.index.constConv(taa.index);
            MATCH mkey = from.next.constConv(taa.next);
            // Pick the worst match
            return mkey < mindex ? mkey : mindex;
        }
        return visitType(from);
    }

    MATCH visitPointer(TypePointer from)
    {
        if (from.next.ty == Tfunction)
        {
            if (to.nextOf() && from.next.equals((cast(TypeNext)to).next))
                return visitType(from);
            else
                return MATCH.nomatch;
        }
        return visitNext(from);
    }

    MATCH visitFunction(TypeFunction from)
    {
        // Attributes need to match exactly, otherwise it's an implicit conversion
        if (from.ty != to.ty || !from.attributesEqual(cast(TypeFunction) to))
            return MATCH.nomatch;

        return visitNext(from);
    }

    MATCH visitStruct(TypeStruct from)
    {
        if (from.equals(to))
            return MATCH.exact;
        if (from.ty == to.ty && from.sym == (cast(TypeStruct)to).sym && MODimplicitConv(from.mod, to.mod))
            return MATCH.constant;
        return MATCH.nomatch;
    }

    MATCH visitEnum(TypeEnum from)
    {
        if (from.equals(to))
            return MATCH.exact;
        if (from.ty == to.ty && from.sym == (cast(TypeEnum)to).sym && MODimplicitConv(from.mod, to.mod))
            return MATCH.constant;
        return MATCH.nomatch;
    }

    MATCH visitClass(TypeClass from)
    {
        if (from.equals(to))
            return MATCH.exact;
        if (from.ty == to.ty && from.sym == (cast(TypeClass)to).sym && MODimplicitConv(from.mod, to.mod))
            return MATCH.constant;

        /* Conversion derived to const(base)
         */
        int offset = 0;
        if (to.isBaseOf(from, &offset) && offset == 0 && MODimplicitConv(from.mod, to.mod))
        {
            // Disallow:
            //  derived to base
            //  inout(derived) to inout(base)
            if (!to.isMutable() && !to.isWild())
                return MATCH.convert;
        }

        return MATCH.nomatch;
    }

    MATCH visitNoreturn(TypeNoreturn from)
    {
        // Either another noreturn or conversion to any type
        return from.implicitConvTo(to);
    }

    switch(from.ty)
    {
        default:            return visitType(from);
        case Tsarray:       return visitSArray(from.isTypeSArray());
        case Taarray:       return visitAArray(from.isTypeAArray());
        case Treference:
        case Tdelegate:
        case Tslice:
        case Tarray:        return visitNext(cast(TypeNext)from);
        case Tpointer:      return visitPointer(from.isTypePointer());
        case Tfunction:     return visitFunction(from.isTypeFunction());
        case Tstruct:       return visitStruct(from.isTypeStruct());
        case Tenum:         return visitEnum(from.isTypeEnum());
        case Tclass:        return visitClass(from.isTypeClass());
        case Tnoreturn:     return visitNoreturn(from.isTypeNoreturn());
    }
}


/******************************************
 * Perform semantic analysis on a type.
 * Params:
 *      type = Type AST node
 *      loc = the location of the type
 *      sc = context
 * Returns:
 *      `Type` with completed semantic analysis, `Terror` if errors
 *      were encountered
 */
Type typeSemantic(Type type, Loc loc, Scope* sc)
{
    static Type error()
    {
        return Type.terror;
    }

    Type visitType(Type t)
    {
        // @@@DEPRECATED_2.110@@@
        // Use of `cent` and `ucent` has always been an error.
        // Starting from 2.100, recommend core.int128 as a replace for the
        // lack of compiler support.
        if (t.ty == Tint128 || t.ty == Tuns128)
        {
            .error(loc, "`cent` and `ucent` types are obsolete, use `core.int128.Cent` instead");
            return error();
        }

        return t.merge();
    }

    Type visitComplex(TypeBasic t)
    {
        if (!sc.inCfile)
            return visitType(t);

        auto tc = getComplexLibraryType(loc, sc, t.ty);
        if (tc.ty == Terror)
            return tc;
        return tc.addMod(t.mod).merge();
    }

    Type visitVector(TypeVector mtype)
    {
        const errors = global.errors;
        mtype.basetype = mtype.basetype.typeSemantic(loc, sc);
        if (errors != global.errors)
            return error();
        mtype.basetype = mtype.basetype.toBasetype().mutableOf();
        if (mtype.basetype.ty != Tsarray)
        {
            .error(loc, "T in __vector(T) must be a static array, not `%s`", mtype.basetype.toChars());
            return error();
        }
        TypeSArray t = mtype.basetype.isTypeSArray();
        const sz = cast(int)t.size(loc);
        final switch (target.isVectorTypeSupported(sz, t.nextOf()))
        {
        case 0:
            // valid
            break;

        case 1:
            // no support at all
            .error(loc, "SIMD vector types not supported on this platform");
            return error();

        case 2:
            // invalid base type
            .error(loc, "vector type `%s` is not supported on this platform", mtype.toChars());
            return error();

        case 3:
            // invalid size
            .error(loc, "%d byte vector type `%s` is not supported on this platform", sz, mtype.toChars());
            return error();
        }
        return merge(mtype);
    }

    Type visitSArray(TypeSArray mtype)
    {
        //printf("TypeSArray::semantic() %s\n", toChars());
        Type t;
        Expression e;
        Dsymbol s;
        mtype.next.resolve(loc, sc, e, t, s);

        if (auto tup = s ? s.isTupleDeclaration() : null)
        {
            mtype.dim = semanticLength(sc, tup, mtype.dim);
            mtype.dim = mtype.dim.ctfeInterpret();
            if (mtype.dim.op == EXP.error)
                return error();

            uinteger_t d = mtype.dim.toUInteger();
            if (d >= tup.objects.length)
            {
                .error(loc, "sequence index `%llu` out of bounds `[0 .. %llu]`", cast(ulong)d, cast(ulong)tup.objects.length);
                return error();
            }

            RootObject o = (*tup.objects)[cast(size_t)d];
            if (auto tt = o.isType())
                return tt.addMod(mtype.mod);
            .error(loc, "`%s` is not a type", mtype.toChars());
            return error();
        }

        if (t && t.ty == Terror)
            return error();

        Type tn = mtype.next.typeSemantic(loc, sc);
        if (tn.ty == Terror)
            return error();

        Type tbn = tn.toBasetype();
        if (mtype.dim)
        {
            auto errors = global.errors;
            mtype.dim = semanticLength(sc, tbn, mtype.dim);
            mtype.dim = mtype.dim.implicitCastTo(sc, Type.tsize_t);
            if (errors != global.errors)
                return error();

            mtype.dim = mtype.dim.optimize(WANTvalue);
            mtype.dim = mtype.dim.ctfeInterpret();
            if (mtype.dim.op == EXP.error)
                return error();

            errors = global.errors;
            dinteger_t d1 = mtype.dim.toInteger();
            if (errors != global.errors)
                return error();

            mtype.dim = mtype.dim.implicitCastTo(sc, Type.tsize_t);
            mtype.dim = mtype.dim.optimize(WANTvalue);
            if (mtype.dim.op == EXP.error)
                return error();

            errors = global.errors;
            dinteger_t d2 = mtype.dim.toInteger();
            if (errors != global.errors)
                return error();

            if (mtype.dim.op == EXP.error)
                return error();

            Type overflowError()
            {
                .error(loc, "`%s` size %llu * %llu exceeds 0x%llx size limit for static array",
                        mtype.toChars(), cast(ulong)tbn.size(loc), cast(ulong)d1, target.maxStaticDataSize);
                return error();
            }

            if (d1 != d2)
                return overflowError();

            Type tbx = tbn.baseElemOf();
            if (tbx.ty == Tstruct && !tbx.isTypeStruct().sym.members ||
                tbx.ty == Tenum && !tbx.isTypeEnum().sym.members)
            {
                /* To avoid meaningless error message, skip the total size limit check
                 * when the bottom of element type is opaque.
                 */
            }
            else if (tbn.isTypeBasic() ||
                     tbn.ty == Tpointer ||
                     tbn.ty == Tarray ||
                     tbn.ty == Tsarray ||
                     tbn.ty == Taarray ||
                     (tbn.ty == Tstruct && tbn.isTypeStruct().sym.sizeok == Sizeok.done) ||
                     tbn.ty == Tclass)
            {
                /* Only do this for types that don't need to have semantic()
                 * run on them for the size, since they may be forward referenced.
                 */
                bool overflow = false;
                if (mulu(tbn.size(loc), d2, overflow) > target.maxStaticDataSize || overflow)
                    return overflowError();
            }
        }
        switch (tbn.ty)
        {
        case Ttuple:
            {
                // Index the tuple to get the type
                assert(mtype.dim);
                TypeTuple tt = tbn.isTypeTuple();
                uinteger_t d = mtype.dim.toUInteger();
                if (d >= tt.arguments.length)
                {
                    .error(loc, "sequence index `%llu` out of bounds `[0 .. %llu]`", cast(ulong)d, cast(ulong)tt.arguments.length);
                    return error();
                }
                Type telem = (*tt.arguments)[cast(size_t)d].type;
                return telem.addMod(mtype.mod);
            }

        case Tfunction:
        case Tnone:
            .error(loc, "cannot have array of `%s`", tbn.toChars());
            return error();

        default:
            break;
        }
        if (tbn.isScopeClass())
        {
            .error(loc, "cannot have array of scope `%s`", tbn.toChars());
            return error();
        }

        /* Ensure things like const(immutable(T)[3]) become immutable(T[3])
         * and const(T)[3] become const(T[3])
         */
        mtype.next = tn;
        mtype.transitive();
        return mtype.addMod(tn.mod).merge();
    }

    Type visitDArray(TypeDArray mtype)
    {
        Type tn = mtype.next.typeSemantic(loc, sc);
        Type tbn = tn.toBasetype();
        switch (tbn.ty)
        {
        case Ttuple:
            return tbn;

        case Tfunction:
        case Tnone:
            .error(loc, "cannot have array of `%s`", tbn.toChars());
            return error();

        case Terror:
            return error();

        default:
            break;
        }
        if (tn.isScopeClass())
        {
            .error(loc, "cannot have array of scope `%s`", tn.toChars());
            return error();
        }
        mtype.next = tn;
        mtype.transitive();
        return merge(mtype);
    }

    Type visitAArray(TypeAArray mtype)
    {
        //printf("TypeAArray::semantic() %s index.ty = %d\n", mtype.toChars(), mtype.index.ty);
        if (mtype.deco)
        {
            return mtype;
        }

        mtype.loc = loc;
        if (sc)
            sc.setNoFree();

        // Deal with the case where we thought the index was a type, but
        // in reality it was an expression.
        if (mtype.index.ty == Tident || mtype.index.ty == Tinstance || mtype.index.ty == Tsarray || mtype.index.ty == Ttypeof || mtype.index.ty == Treturn || mtype.index.ty == Tmixin)
        {
            Expression e;
            Type t;
            Dsymbol s;
            mtype.index.resolve(loc, sc, e, t, s);

            // https://issues.dlang.org/show_bug.cgi?id=15478
            if (s)
                e = symbolToExp(s, loc, sc, false);

            if (e)
            {
                // It was an expression -
                // Rewrite as a static array
                auto tsa = new TypeSArray(mtype.next, e);
                return tsa.typeSemantic(loc, sc);
            }
            else if (t)
                mtype.index = t.typeSemantic(loc, sc);
            else
            {
                .error(loc, "index is not a type or an expression");
                return error();
            }
        }
        else
            mtype.index = mtype.index.typeSemantic(loc, sc);
        mtype.index = mtype.index.merge2();

        if (mtype.index.nextOf() && !mtype.index.nextOf().isImmutable())
        {
            mtype.index = mtype.index.constOf().mutableOf();
            version (none)
            {
                printf("index is %p %s\n", mtype.index, mtype.index.toChars());
                mtype.index.check();
                printf("index.mod = x%x\n", mtype.index.mod);
                printf("index.ito = x%p\n", mtype.index.getMcache().ito);
                if (mtype.index.getMcache().ito)
                {
                    printf("index.ito.mod = x%x\n", mtype.index.getMcache().ito.mod);
                    printf("index.ito.ito = x%p\n", mtype.index.getMcache().ito.getMcache().ito);
                }
            }
        }

        switch (mtype.index.toBasetype().ty)
        {
        case Tfunction:
        case Tvoid:
        case Tnone:
        case Ttuple:
            .error(loc, "cannot have associative array key of `%s`", mtype.index.toBasetype().toChars());
            goto case Terror;
        case Terror:
            return error();

        default:
            break;
        }
        Type tbase = mtype.index.baseElemOf();
        while (tbase.ty == Tarray)
            tbase = tbase.nextOf().baseElemOf();
        if (auto ts = tbase.isTypeStruct())
        {
            /* AA's need typeid(index).equals() and getHash(). Issue error if not correctly set up.
             */
            StructDeclaration sd = ts.sym;
            if (sd.semanticRun < PASS.semanticdone)
                sd.dsymbolSemantic(null);

            // duplicate a part of StructDeclaration::semanticTypeInfoMembers
            //printf("AA = %s, key: xeq = %p, xerreq = %p xhash = %p\n", toChars(), sd.xeq, sd.xerreq, sd.xhash);

            if (sd.xeq && sd.xeq.isGenerated() && sd.xeq._scope && sd.xeq.semanticRun < PASS.semantic3done)
            {
                uint errors = global.startGagging();
                sd.xeq.semantic3(sd.xeq._scope);
                if (global.endGagging(errors))
                    sd.xeq = sd.xerreq;
            }


            //printf("AA = %s, key: xeq = %p, xhash = %p\n", toChars(), sd.xeq, sd.xhash);
            const(char)* s = (mtype.index.toBasetype().ty != Tstruct) ? "bottom of " : "";
            if (!sd.xeq)
            {
                // If sd.xhash != NULL:
                //   sd or its fields have user-defined toHash.
                //   AA assumes that its result is consistent with bitwise equality.
                // else:
                //   bitwise equality & hashing
            }
            else if (sd.xeq == sd.xerreq)
            {
                if (search_function(sd, Id.opEquals))
                {
                    .error(loc, "%sAA key type `%s` does not have `bool opEquals(ref const %s) const`", s, sd.toChars(), sd.toChars());
                }
                else
                {
                    .error(loc, "%sAA key type `%s` does not support const equality", s, sd.toChars());
                }
                return error();
            }
            else if (!sd.xhash)
            {
                if (search_function(sd, Id.opEquals))
                {
                    .error(loc, "%sAA key type `%s` should have `extern (D) size_t toHash() const nothrow @safe` if `opEquals` defined", s, sd.toChars());
                }
                else
                {
                    .error(loc, "%sAA key type `%s` supports const equality but doesn't support const hashing", s, sd.toChars());
                }
                return error();
            }
            else
            {
                // defined equality & hashing
                assert(sd.xeq && sd.xhash);

                /* xeq and xhash may be implicitly defined by compiler. For example:
                 *   struct S { int[] arr; }
                 * With 'arr' field equality and hashing, compiler will implicitly
                 * generate functions for xopEquals and xtoHash in TypeInfo_Struct.
                 */
            }
        }
        else if (tbase.ty == Tclass && !tbase.isTypeClass().sym.isInterfaceDeclaration())
        {
            ClassDeclaration cd = tbase.isTypeClass().sym;
            if (cd.semanticRun < PASS.semanticdone)
                cd.dsymbolSemantic(null);

            if (!ClassDeclaration.object)
            {
                ObjectNotFound(Loc.initial, cd.ident);
                return error();
            }

            __gshared FuncDeclaration feq = null;
            __gshared FuncDeclaration fcmp = null;
            __gshared FuncDeclaration fhash = null;
            if (!feq)
                feq = search_function(ClassDeclaration.object, Id.opEquals).isFuncDeclaration();
            if (!fcmp)
                fcmp = search_function(ClassDeclaration.object, Id.opCmp).isFuncDeclaration();
            if (!fhash)
                fhash = search_function(ClassDeclaration.object, Id.tohash).isFuncDeclaration();
            assert(fcmp && feq && fhash);

            if (feq.vtblIndex < cd.vtbl.length && cd.vtbl[feq.vtblIndex] == feq)
            {
                version (all)
                {
                    if (fcmp.vtblIndex < cd.vtbl.length && cd.vtbl[fcmp.vtblIndex] != fcmp)
                    {
                        const(char)* s = (mtype.index.toBasetype().ty != Tclass) ? "bottom of " : "";
                        .error(loc, "%sAA key type `%s` now requires equality rather than comparison", s, cd.toChars());
                        errorSupplemental(loc, "Please override `Object.opEquals` and `Object.toHash`.");
                    }
                }
            }
        }
        mtype.next = mtype.next.typeSemantic(loc, sc).merge2();
        mtype.transitive();

        switch (mtype.next.toBasetype().ty)
        {
        case Tfunction:
        case Tvoid:
        case Tnone:
        case Ttuple:
            .error(loc, "cannot have associative array of `%s`", mtype.next.toChars());
            goto case Terror;
        case Terror:
            return error();
        default:
            break;
        }
        if (mtype.next.isScopeClass())
        {
            .error(loc, "cannot have array of scope `%s`", mtype.next.toChars());
            return error();
        }
        return merge(mtype);
    }

    Type visitPointer(TypePointer mtype)
    {
        //printf("TypePointer::semantic() %s\n", toChars());
        if (mtype.deco)
        {
            return mtype;
        }
        Type n = mtype.next.typeSemantic(loc, sc);
        switch (n.toBasetype().ty)
        {
        case Ttuple:
            .error(loc, "cannot have pointer to `%s`", n.toChars());
            goto case Terror;
        case Terror:
            return error();
        default:
            break;
        }
        if (n != mtype.next)
        {
            mtype.deco = null;
        }
        mtype.next = n;
        if (mtype.next.ty != Tfunction)
        {
            mtype.transitive();
            return merge(mtype);
        }
        version (none)
        {
            return merge(mtype);
        }
        else
        {
            mtype.deco = merge(mtype).deco;
            /* Don't return merge(), because arg identifiers and default args
             * can be different
             * even though the types match
             */
            return mtype;
        }
    }

    Type visitReference(TypeReference mtype)
    {
        //printf("TypeReference::semantic()\n");
        Type n = mtype.next.typeSemantic(loc, sc);
        if (n != mtype.next)
           mtype.deco = null;
        mtype.next = n;
        mtype.transitive();
        return merge(mtype);
    }

    Type visitFunction(TypeFunction mtype)
    {
        if (mtype.deco) // if semantic() already run
        {
            //printf("already done\n");
            return mtype;
        }
        //printf("TypeFunction::semantic() this = %p\n", mtype);
        //printf("TypeFunction::semantic() %s, sc.stc = %llx\n", mtype.toChars(), sc.stc);

        bool errors = false;

        if (mtype.inuse > global.recursionLimit)
        {
            mtype.inuse = 0;
            .error(loc, "recursive type");
            return error();
        }

        /* Copy in order to not mess up original.
         * This can produce redundant copies if inferring return type,
         * as semantic() will get called again on this.
         */
        TypeFunction tf = mtype.copy().toTypeFunction();
        if (mtype.parameterList.parameters)
        {
            tf.parameterList.parameters = mtype.parameterList.parameters.copy();
            for (size_t i = 0; i < mtype.parameterList.parameters.length; i++)
            {
                Parameter p = cast(Parameter)mem.xmalloc(__traits(classInstanceSize, Parameter));
                memcpy(cast(void*)p, cast(void*)(*mtype.parameterList.parameters)[i], __traits(classInstanceSize, Parameter));
                (*tf.parameterList.parameters)[i] = p;
            }
        }

        if (sc.stc & STC.pure_)
            tf.purity = PURE.fwdref;
        if (sc.stc & STC.nothrow_)
            tf.isNothrow = true;
        if (sc.stc & STC.nogc)
            tf.isNogc = true;
        if (sc.stc & STC.ref_)
            tf.isRef = true;
        if (sc.stc & STC.return_)
            tf.isReturn = true;
        if (sc.stc & STC.returnScope)
            tf.isReturnScope = true;
        if (sc.stc & STC.returninferred)
            tf.isReturnInferred = true;
        if (sc.stc & STC.scope_)
            tf.isScopeQual = true;
        if (sc.stc & STC.scopeinferred)
            tf.isScopeInferred = true;

//        if (tf.isReturn && !tf.isRef)
//            tf.isScopeQual = true;                                  // return by itself means 'return scope'

        if (tf.trust == TRUST.default_)
        {
            if (sc.stc & STC.safe)
                tf.trust = TRUST.safe;
            else if (sc.stc & STC.system)
                tf.trust = TRUST.system;
            else if (sc.stc & STC.trusted)
                tf.trust = TRUST.trusted;
        }

        if (sc.stc & STC.property)
            tf.isProperty = true;
        if (sc.stc & STC.live)
            tf.isLive = true;

        tf.linkage = sc.linkage;
        if (tf.linkage == LINK.system)
            tf.linkage = target.systemLinkage();

        version (none)
        {
            /* If the parent is @safe, then this function defaults to safe
             * too.
             * If the parent's @safe-ty is inferred, then this function's @safe-ty needs
             * to be inferred first.
             */
            if (tf.trust == TRUST.default_)
                for (Dsymbol p = sc.func; p; p = p.toParent2())
                {
                    FuncDeclaration fd = p.isFuncDeclaration();
                    if (fd)
                    {
                        if (fd.isSafeBypassingInference())
                            tf.trust = TRUST.safe; // default to @safe
                        break;
                    }
                }
        }

        bool wildreturn = false;
        if (tf.next)
        {
            sc = sc.push();
            sc.stc &= ~(STC.TYPECTOR | STC.FUNCATTR);
            tf.next = tf.next.typeSemantic(loc, sc);
            sc = sc.pop();
            errors |= tf.checkRetType(loc);
            if (tf.next.isScopeClass() && !tf.isCtor)
            {
                .error(loc, "functions cannot return `scope %s`", tf.next.toChars());
                errors = true;
            }
            if (tf.next.hasWild())
                wildreturn = true;

            if (tf.isReturn && !tf.isRef && !tf.next.hasPointers())
            {
                tf.isReturn = false;
            }
        }

        /// Perform semantic on the default argument to a parameter
        /// Modify the `defaultArg` field of `fparam`, which must not be `null`
        /// Returns `false` whether an error was encountered.
        static bool defaultArgSemantic (ref Parameter fparam, Scope* sc)
        {
            Expression e = fparam.defaultArg;
            const isRefOrOut = fparam.isReference();
            const isAuto = fparam.storageClass & (STC.auto_ | STC.autoref);
            if (isRefOrOut && !isAuto)
            {
                e = e.expressionSemantic(sc);
                e = resolveProperties(sc, e);
            }
            else
            {
                e = inferType(e, fparam.type);
                Scope* sc2 = sc.push();
                sc2.inDefaultArg = true;
                Initializer iz = new ExpInitializer(e.loc, e);
                iz = iz.initializerSemantic(sc2, fparam.type, INITnointerpret);
                e = iz.initializerToExpression();
                sc2.pop();
            }
            if (e.op == EXP.function_) // https://issues.dlang.org/show_bug.cgi?id=4820
            {
                FuncExp fe = e.isFuncExp();
                // Replace function literal with a function symbol,
                // since default arg expression must be copied when used
                // and copying the literal itself is wrong.
                e = new VarExp(e.loc, fe.fd, false);
                e = new AddrExp(e.loc, e);
                e = e.expressionSemantic(sc);
            }
            if (isRefOrOut && (!isAuto || e.isLvalue())
                && !MODimplicitConv(e.type.mod, fparam.type.mod))
            {
                const(char)* errTxt = fparam.storageClass & STC.ref_ ? "ref" : "out";
                .error(e.loc, "expression `%s` of type `%s` is not implicitly convertible to type `%s %s` of parameter `%s`",
                      e.toErrMsg(), e.type.toChars(), errTxt, fparam.type.toChars(), fparam.toChars());
            }
            e = e.implicitCastTo(sc, fparam.type);

            // default arg must be an lvalue
            if (isRefOrOut && !isAuto &&
                !(fparam.storageClass & STC.constscoperef) && !sc.previews.rvalueRefParam)
                e = e.toLvalue(sc, "create default argument for `ref` / `out` parameter from");

            fparam.defaultArg = e;
            return (e.op != EXP.error);
        }

        ubyte wildparams = 0;
        if (tf.parameterList.parameters)
        {
            /* Create a scope for evaluating the default arguments for the parameters
             */
            Scope* argsc = sc.push();
            argsc.stc = STC.none; // don't inherit storage class
            argsc.visibility = Visibility(Visibility.Kind.public_);
            argsc.func = null;

            size_t dim = tf.parameterList.length;
            for (size_t i = 0; i < dim; i++)
            {
                Parameter fparam = tf.parameterList[i];
                fparam.storageClass |= STC.parameter;
                mtype.inuse++;
                fparam.type = fparam.type.typeSemantic(loc, argsc);
                mtype.inuse--;

                if (fparam.type.ty == Terror)
                {
                    errors = true;
                    continue;
                }

                fparam.type = fparam.type.addStorageClass(fparam.storageClass);

                if (fparam.storageClass & (STC.auto_ | STC.alias_ | STC.static_))
                {
                    if (!fparam.type)
                        continue;
                }

                fparam.type = fparam.type.cAdjustParamType(sc); // adjust C array and function parameter types

                Type t = fparam.type.toBasetype();

                /* If fparam after semantic() turns out to be a tuple, the number of parameters may
                 * change.
                 */
                if (auto tt = t.isTypeTuple())
                {
                    /* TypeFunction::parameter also is used as the storage of
                     * Parameter objects for FuncDeclaration. So we should copy
                     * the elements of TypeTuple::arguments to avoid unintended
                     * sharing of Parameter object among other functions.
                     */
                    if (tt.arguments && tt.arguments.length)
                    {
                        /* Propagate additional storage class from tuple parameters to their
                         * element-parameters.
                         * Make a copy, as original may be referenced elsewhere.
                         */
                        size_t tdim = tt.arguments.length;
                        auto newparams = new Parameters(tdim);
                        for (size_t j = 0; j < tdim; j++)
                        {
                            Parameter narg = (*tt.arguments)[j];

                            // https://issues.dlang.org/show_bug.cgi?id=12744
                            // If the storage classes of narg
                            // conflict with the ones in fparam, it's ignored.
                            STC stc  = fparam.storageClass | narg.storageClass;
                            STC stc1 = fparam.storageClass & (STC.ref_ | STC.out_ | STC.lazy_);
                            STC stc2 =   narg.storageClass & (STC.ref_ | STC.out_ | STC.lazy_);
                            if (stc1 && stc2 && stc1 != stc2)
                            {
                                OutBuffer buf1;  stcToBuffer(buf1, stc1 | ((stc1 & STC.ref_) ? (fparam.storageClass & STC.auto_) : STC.none));
                                OutBuffer buf2;  stcToBuffer(buf2, stc2);

                                .error(loc, "incompatible parameter storage classes `%s` and `%s`",
                                    buf1.peekChars(), buf2.peekChars());
                                errors = true;
                                stc = stc1 | (stc & ~(STC.ref_ | STC.out_ | STC.lazy_));
                            }
                            (*newparams)[j] = new Parameter(
                                loc, stc, narg.type, narg.ident, narg.defaultArg, narg.userAttribDecl);
                        }
                        fparam.type = new TypeTuple(newparams);
                        fparam.type = fparam.type.typeSemantic(loc, argsc);
                    }
                    fparam.storageClass = STC.parameter;

                    /* Reset number of parameters, and back up one to do this fparam again,
                     * now that it is a tuple
                     */
                    dim = tf.parameterList.length;
                    i--;
                    continue;
                }

                // -preview=in: Always add `ref` when used with `extern(C++)` functions
                // Done here to allow passing opaque types with `in`
                if ((fparam.storageClass & (STC.in_ | STC.ref_)) == STC.in_)
                {
                    switch (tf.linkage)
                    {
                    case LINK.cpp:
                        if (fparam.storageClass & STC.constscoperef)
                            fparam.storageClass |= STC.ref_;
                        break;
                    case LINK.default_, LINK.d:
                        break;
                    default:
                        if (fparam.storageClass & STC.constscoperef)
                        {
                            .error(loc, "cannot use `in` parameters with `extern(%s)` functions",
                                   linkageToChars(tf.linkage));
                            .errorSupplemental(loc, "parameter `%s` declared as `in` here", fparam.toChars());
                        }
                        else
                        {
                            // Note that this deprecation will not trigger on `in ref` / `ref in`
                            // parameters, however the parser will trigger a deprecation on them.
                            .deprecation(loc, "using `in` parameters with `extern(%s)` functions is deprecated",
                                         linkageToChars(tf.linkage));
                            .deprecationSupplemental(loc, "parameter `%s` declared as `in` here", fparam.toChars());
                        }
                        break;
                    }
                }

                if (t.ty == Tfunction)
                {
                    .error(loc, "cannot have parameter of function type `%s`", fparam.type.toChars());
                    errors = true;
                }
                else if (!fparam.isReference() &&
                         (t.ty == Tstruct || t.ty == Tsarray || t.ty == Tenum))
                {
                    Type tb2 = t.baseElemOf();
                    if (tb2.ty == Tstruct && !tb2.isTypeStruct().sym.members ||
                        tb2.ty == Tenum   && !tb2.isTypeEnum().sym.memtype)
                    {
                        if (fparam.storageClass & STC.constscoperef)
                        {
                            .error(loc, "cannot infer `ref` for `in` parameter `%s` of opaque type `%s`",
                                   fparam.toChars(), fparam.type.toChars());
                        }
                        else
                            .error(loc, "cannot have parameter of opaque type `%s` by value",
                                   fparam.type.toChars());
                        errors = true;
                    }
                }
                else if (!fparam.isLazy() && t.ty == Tvoid)
                {
                    .error(loc, "cannot have parameter of type `%s`", fparam.type.toChars());
                    errors = true;
                }

                const bool isTypesafeVariadic = i + 1 == dim && tf.parameterList.varargs == VarArg.typesafe;
                const bool isStackAllocatedVariadic = isTypesafeVariadic && (t.isTypeDArray() || t.isTypeClass());

                if (isTypesafeVariadic && t.isTypeClass())
                {
                    // Deprecated in 2.111, kept as a legacy feature for compatibility (currently no plan to turn it into an error)
                    .deprecation(loc, "typesafe variadic parameters with a `class` type (`%s %s...`) are deprecated",
                        t.isTypeClass().sym.ident.toChars(), fparam.toChars());
                }

                if (isStackAllocatedVariadic)
                {
                    /* typesafe variadic arguments are constructed on the stack, so must be `scope`
                     */
                    fparam.storageClass |= STC.scope_ | STC.scopeinferred;
                }

                if (fparam.storageClass & STC.return_)
                {
                    if (!fparam.isReference())
                    {
                        if (!(fparam.storageClass & STC.scope_))
                            fparam.storageClass |= STC.scope_ | STC.scopeinferred; // 'return' implies 'scope'
                        if (tf.isRef)
                        {
                        }
                        else if (tf.next && !tf.next.hasPointers() && tf.next.toBasetype().ty != Tvoid)
                        {
                            fparam.storageClass &= ~STC.return_;   // https://issues.dlang.org/show_bug.cgi?id=18963
                        }
                    }

                    if (isStackAllocatedVariadic)
                    {
                        /* This is because they can be constructed on the stack
                         * https://dlang.org/spec/function.html#typesafe_variadic_functions
                         */
                        .error(loc, "typesafe variadic function parameter `%s` of type `%s` cannot be marked `return`",
                            fparam.ident ? fparam.ident.toChars() : "", t.toChars());
                        errors = true;
                    }
                }

                if (fparam.storageClass & STC.out_)
                {
                    if (ubyte m = fparam.type.mod & (MODFlags.immutable_ | MODFlags.const_ | MODFlags.wild))
                    {
                        .error(loc, "cannot have `%s out` parameter of type `%s`", MODtoChars(m), t.toChars());
                        errors = true;
                    }
                    else
                    {
                        Type tv = t.baseElemOf();
                        if (tv.ty == Tstruct && tv.isTypeStruct().sym.noDefaultCtor)
                        {
                            .error(loc, "cannot have `out` parameter of type `%s` because the default construction is disabled", fparam.type.toChars());
                            errors = true;
                        }
                    }
                }

                if (t.hasWild())
                {
                    wildparams |= 1;
                    //if (tf.next && !wildreturn)
                    //    error(loc, "inout on parameter means inout must be on return type as well (if from D1 code, replace with `ref`)");
                }

                // Remove redundant storage classes for type, they are already applied
                fparam.storageClass &= ~(STC.TYPECTOR);

                // -preview=in: add `ref` storage class to suited `in` params
                if ((fparam.storageClass & (STC.constscoperef | STC.ref_)) == STC.constscoperef)
                {
                    auto ts = t.baseElemOf().isTypeStruct();
                    const isPOD = !ts || ts.sym.isPOD();
                    if (!isPOD || target.preferPassByRef(t))
                        fparam.storageClass |= STC.ref_;
                }
            }

            Expressions* fargs = mtype.inferenceArguments.arguments;

            // mtype.argumentList only provided for Implicit Function Template Instantiation
            if (mtype.inferenceArguments.length > 0)
                fargs = tf.resolveNamedArgs(mtype.inferenceArguments, null);

            // Now that we completed semantic for the argument types,
            // run semantic on their default values,
            // bearing in mind tuples have been expanded.
            // We need to keep a pair of [oidx, eidx] (original index,
            // extended index), as we need to run semantic when `oidx` changes.
            size_t tupleOrigIdx = size_t.max;
            size_t tupleExtIdx = size_t.max;
            foreach (oidx, oparam, eidx, eparam; tf.parameterList)
            {
                // oparam (original param) will always have the default arg
                // if there's one, but `eparam` will not if it's an expanded
                // tuple. When we see an expanded tuple, we need to save its
                // position to get the offset in it later on.
                if (oparam.defaultArg)
                {
                    // Get the obvious case out of the way
                    if (oparam is eparam)
                        errors |= !defaultArgSemantic(eparam, argsc);
                    // We're seeing a new tuple
                    else if (tupleOrigIdx == size_t.max || tupleOrigIdx < oidx)
                    {
                        /* https://issues.dlang.org/show_bug.cgi?id=18572
                         *
                         * If a tuple parameter has a default argument, when expanding the parameter
                         * tuple the default argument tuple must also be expanded.
                         */
                        tupleOrigIdx = oidx;
                        tupleExtIdx = eidx;
                        errors |= !defaultArgSemantic(oparam, argsc);
                        TupleExp te = oparam.defaultArg.isTupleExp();
                        if (te && te.exps && te.exps.length)
                            eparam.defaultArg = (*te.exps)[0];
                    }
                    // Processing an already-seen tuple
                    else
                    {
                        TupleExp te = oparam.defaultArg.isTupleExp();
                        if (te && te.exps && te.exps.length)
                            eparam.defaultArg = (*te.exps)[eidx - tupleExtIdx];
                    }
                }

                // We need to know the default argument to resolve `auto ref`,
                // hence why this has to take place as the very last step.
                /* Resolve "auto ref" storage class to be either ref or value,
                 * based on the argument matching the parameter
                 */
                if (eparam.storageClass & STC.auto_)
                {
                    Expression farg = (fargs && eidx < fargs.length) ? (*fargs)[eidx] : null;
                    if (!farg)
                        farg = eparam.defaultArg;

                    if (farg && (eparam.storageClass & STC.ref_))
                    {
                        if (!farg.isLvalue())
                            eparam.storageClass &= ~STC.ref_; // value parameter
                        eparam.storageClass &= ~STC.auto_;    // https://issues.dlang.org/show_bug.cgi?id=14656
                        eparam.storageClass |= STC.autoref;
                    }
                    else if (mtype.incomplete && (eparam.storageClass & STC.ref_))
                    {
                        // the default argument may have been temporarily removed,
                        // see usage of `TypeFunction.incomplete`.
                        // https://issues.dlang.org/show_bug.cgi?id=19891
                        eparam.storageClass &= ~STC.auto_;
                        eparam.storageClass |= STC.autoref;
                    }
                    else if (eparam.storageClass & STC.ref_)
                    {
                        .error(loc, "cannot explicitly instantiate template function with `auto ref` parameter");
                        errors = true;
                    }
                    else
                    {
                        .error(loc, "`auto` can only be used as part of `auto ref` for template function parameters");
                        errors = true;
                    }
                }
            }

            argsc.pop();
        }
        if (tf.isWild())
            wildparams |= 2;

        if (wildreturn && !wildparams)
        {
            .error(loc, "`inout` on `return` means `inout` must be on a parameter as well for `%s`", mtype.toChars());
            errors = true;
        }
        tf.isInOutParam = (wildparams & 1) != 0;
        tf.isInOutQual  = (wildparams & 2) != 0;

        if (tf.isProperty && (tf.parameterList.varargs != VarArg.none || tf.parameterList.length > 2))
        {
            .error(loc, "properties can only have zero, one, or two parameter");
            errors = true;
        }

        if (tf.parameterList.varargs == VarArg.variadic && tf.linkage != LINK.d && tf.parameterList.length == 0 &&
            !sc.inCfile)
        {
            .error(loc, "variadic functions with non-D linkage must have at least one parameter");
            errors = true;
        }

        if (errors)
            return error();

        if (tf.next)
            tf.deco = tf.merge().deco;

        /* Don't return merge(), because arg identifiers and default args
         * can be different
         * even though the types match
         */
        return tf;
    }

    Type visitDelegate(TypeDelegate mtype)
    {
        //printf("TypeDelegate::semantic() %s\n", mtype.toChars());
        if (mtype.deco) // if semantic() already run
        {
            //printf("already done\n");
            return mtype;
        }
        mtype.next = mtype.next.typeSemantic(loc, sc);
        if (mtype.next.ty != Tfunction)
            return error();

        /* In order to deal with https://issues.dlang.org/show_bug.cgi?id=4028
         * perhaps default arguments should
         * be removed from next before the merge.
         */
        version (none)
        {
            return mtype.merge();
        }
        else
        {
            /* Don't return merge(), because arg identifiers and default args
             * can be different
             * even though the types match
             */
            mtype.deco = mtype.merge().deco;
            return mtype;
        }
    }

    Type visitIdentifier(TypeIdentifier mtype)
    {
        Type t;
        Expression e;
        Dsymbol s;
        //printf("TypeIdentifier::semantic(%s)\n", mtype.toChars());
        mtype.resolve(loc, sc, e, t, s);
        if (t)
        {
            //printf("\tit's a type %d, %s, %s\n", t.ty, t.toChars(), t.deco);
            return t.addMod(mtype.mod);
        }

        if (s)
        {
            auto td = s.isTemplateDeclaration;
            if (td && td.onemember && td.onemember.isAggregateDeclaration)
                .error(loc, "template %s `%s` is used as a type without instantiation"
                    ~ "; to instantiate it use `%s!(arguments)`",
                    s.kind, s.toPrettyChars, s.ident.toChars);
            else
                .error(loc, "%s `%s` is used as a type", s.kind, s.toPrettyChars);
            //assert(0);
        }
        else if (e.op == EXP.variable) // special case: variable is used as a type
        {
            /*
                N.B. This branch currently triggers for the following code
                template test(x* x)
                {

                }
                i.e. the compiler prints "variable x is used as a type"
                which isn't a particularly good error message (x is a variable?).
            */
            Dsymbol varDecl = mtype.toDsymbol(sc);
            Module varDeclModule = varDecl.getModule(); //This can be null

            .error(loc, "variable `%s` is used as a type", mtype.toChars());
            //Check for null to avoid https://issues.dlang.org/show_bug.cgi?id=22574
            if ((varDeclModule !is null) && varDeclModule != sc._module) // variable is imported
            {
                .errorSupplemental(
                    varDeclModule.loc,
                    "variable `%s` is imported here from: `%s`",
                    varDecl.toChars,
                    varDeclModule.toPrettyChars,
                );
            }

            .errorSupplemental(varDecl.loc, "variable `%s` is declared here", varDecl.toChars);
        }
        else
            .error(loc, "`%s` is used as a type", mtype.toChars());
        return error();
    }

    Type visitInstance(TypeInstance mtype)
    {
        Type t;
        Expression e;
        Dsymbol s;

        //printf("TypeInstance::semantic(%p, %s)\n", this, toChars());
        {
            const errors = global.errors;
            mtype.resolve(loc, sc, e, t, s);
            // if we had an error evaluating the symbol, suppress further errors
            if (!t && errors != global.errors)
                return error();
        }

        if (!t)
        {
            if (!e && s && s.errors)
            {
                // if there was an error evaluating the symbol, it might actually
                // be a type. Avoid misleading error messages.
                .error(loc, "`%s` had previous errors", mtype.toChars());
            }
            else
                .error(loc, "`%s` is used as a type", mtype.toChars());
            return error();
        }
        return t;
    }

    Type visitTypeof(TypeTypeof mtype)
    {
        //printf("TypeTypeof::semantic() %s\n", mtype.toChars());
        Expression e;
        Type t;
        Dsymbol s;
        mtype.resolve(loc, sc, e, t, s);
        if (s && (t = s.getType()) !is null)
            t = t.addMod(mtype.mod);
        if (!t)
        {
            .error(loc, "`%s` is used as a type", mtype.toChars());
            return error();
        }
        return t;
    }

    Type visitTraits(TypeTraits mtype)
    {
        Expression e;
        Type t;
        Dsymbol s;
        mtype.resolve(loc, sc, e, t, s);

        if (!t)
        {
            if (!global.errors)
                .error(mtype.loc, "`%s` does not give a valid type", mtype.toChars);
            return error();
        }
        return t;
    }

    Type visitReturn(TypeReturn mtype)
    {
        //printf("TypeReturn::semantic() %s\n", toChars());
        Expression e;
        Type t;
        Dsymbol s;
        mtype.resolve(loc, sc, e, t, s);
        if (s && (t = s.getType()) !is null)
            t = t.addMod(mtype.mod);
        if (!t)
        {
            .error(loc, "`%s` is used as a type", mtype.toChars());
            return error();
        }
        return t;
    }

    Type visitStruct(TypeStruct mtype)
    {
        //printf("TypeStruct::semantic('%s')\n", mtype.toChars());
        if (mtype.deco)
            return mtype;

        /* Don't semantic for sym because it should be deferred until
         * sizeof needed or its members accessed.
         */
        // instead, parent should be set correctly
        assert(mtype.sym.parent);

        if (mtype.sym.type.ty == Terror)
            return error();

        return merge(mtype);
    }

    Type visitEnum(TypeEnum mtype)
    {
        //printf("TypeEnum::semantic() %s\n", toChars());
        return mtype.deco ? mtype : merge(mtype);
    }

    Type visitClass(TypeClass mtype)
    {
        //printf("TypeClass::semantic(%s)\n", mtype.toChars());
        if (mtype.deco)
            return mtype;

        /* Don't semantic for sym because it should be deferred until
         * sizeof needed or its members accessed.
         */
        // instead, parent should be set correctly
        assert(mtype.sym.parent);

        if (mtype.sym.type.ty == Terror)
            return error();

        return merge(mtype);
    }

    Type visitTuple(TypeTuple mtype)
    {
        //printf("TypeTuple::semantic(this = %p)\n", this);
        //printf("TypeTuple::semantic() %p, %s\n", this, toChars());
        if (!mtype.deco)
            mtype.deco = merge(mtype).deco;

        /* Don't return merge(), because a tuple with one type has the
         * same deco as that type.
         */
        return mtype;
    }

    Type visitSlice(TypeSlice mtype)
    {
        //printf("TypeSlice::semantic() %s\n", toChars());
        Type tn = mtype.next.typeSemantic(loc, sc);
        //printf("next: %s\n", tn.toChars());

        Type tbn = tn.toBasetype();
        if (tbn.ty != Ttuple)
        {
            .error(loc, "can only slice type sequences, not `%s`", tbn.toChars());
            return error();
        }
        TypeTuple tt = cast(TypeTuple)tbn;

        mtype.lwr = semanticLength(sc, tbn, mtype.lwr);
        mtype.upr = semanticLength(sc, tbn, mtype.upr);
        mtype.lwr = mtype.lwr.ctfeInterpret();
        mtype.upr = mtype.upr.ctfeInterpret();
        if (mtype.lwr.op == EXP.error || mtype.upr.op == EXP.error)
            return error();

        uinteger_t i1 = mtype.lwr.toUInteger();
        uinteger_t i2 = mtype.upr.toUInteger();
        if (!(i1 <= i2 && i2 <= tt.arguments.length))
        {
            .error(loc, "slice `[%llu..%llu]` is out of range of `[0..%llu]`",
                cast(ulong)i1, cast(ulong)i2, cast(ulong)tt.arguments.length);
            return error();
        }

        mtype.next = tn;
        mtype.transitive();

        auto args = new Parameters();
        args.reserve(cast(size_t)(i2 - i1));
        foreach (arg; (*tt.arguments)[cast(size_t)i1 .. cast(size_t)i2])
        {
            args.push(arg);
        }
        Type t = new TypeTuple(args);
        return t.typeSemantic(loc, sc);
    }

    Type visitMixin(TypeMixin mtype)
    {
        //printf("TypeMixin::semantic() %s\n", toChars());

        Expression e;
        Type t;
        Dsymbol s;
        mtype.resolve(loc, sc, e, t, s);

        if (t && t.ty != Terror)
            return t;

        .error(mtype.loc, "`mixin(%s)` does not give a valid type", mtype.obj.toChars);
        return error();
    }

    Type visitTag(TypeTag mtype)
    {
        //printf("TypeTag.semantic() %s\n", mtype.toChars());
        Type returnType(TypeTag tt)
        {
            Type t = tt.resolved;
            // To make const checking work, the const STC needs to be added:
            // t = t.resolved.addSTC(mtype.mod.ModToStc);
            // However, this currently fails compilable/test22875.i
            // Apparently there's some aliasing going on, where mutable
            // versions of the type also get const applied to them.
            return t.deco ? t : t.merge();
        }

        if (mtype.resolved)
        {
            /* struct S s, *p;
             */
            return returnType(mtype);
        }

        /* Find the current scope by skipping tag scopes.
         * In C, tag scopes aren't considered scopes.
         */
        Scope* sc2 = sc;
        while (1)
        {
            sc2 = sc2.inner();
            auto scopesym = sc2.scopesym;
            if (scopesym.isStructDeclaration())
            {
                sc2 = sc2.enclosing;
                continue;
            }
            break;
        }

        /* Declare mtype as a struct/union/enum declaration
         */
        void declareTag()
        {
            void declare(ScopeDsymbol sd)
            {
                sd.members = mtype.members;
                auto scopesym = sc2.inner().scopesym;
                if (scopesym.members)
                    scopesym.members.push(sd);
                if (scopesym.symtab && !scopesym.symtabInsert(sd))
                {
                    Dsymbol s2 = scopesym.symtabLookup(sd, mtype.id);
                    handleTagSymbols(*sc2, sd, s2, scopesym);
                }
                sd.parent = sc2.parent;
                sd.dsymbolSemantic(sc2);
            }

            switch (mtype.tok)
            {
                case TOK.enum_:
                    auto ed = new EnumDeclaration(mtype.loc, mtype.id, mtype.base);
                    declare(ed);
                    mtype.resolved = visitEnum(new TypeEnum(ed));
                    break;

                case TOK.struct_:
                    auto sd = new StructDeclaration(mtype.loc, mtype.id, false);
                    sd.alignment = mtype.packalign;
                    declare(sd);
                    mtype.resolved = visitStruct(new TypeStruct(sd));
                    break;

                case TOK.union_:
                    auto ud = new UnionDeclaration(mtype.loc, mtype.id);
                    ud.alignment = mtype.packalign;
                    declare(ud);
                    mtype.resolved = visitStruct(new TypeStruct(ud));
                    break;

                default:
                    assert(0);
            }
        }

        /* If it doesn't have a tag by now, supply one.
         * It'll be unique, and therefore introducing.
         * Declare it, and done.
         */
        if (!mtype.id)
        {
            mtype.id = Identifier.generateId("__tag"[]);
            declareTag();
            return returnType(mtype);
        }

        /* look for pre-existing declaration
         */
        Dsymbol scopesym;
        auto s = sc2.search(mtype.loc, mtype.id, scopesym, SearchOpt.ignoreErrors | SearchOpt.tagNameSpace);
        if (!s || s.isModule())
        {
            // no pre-existing declaration, so declare it
            if (mtype.tok == TOK.enum_ && !mtype.members)
                .error(mtype.loc, "`enum %s` is incomplete without members", mtype.id.toChars()); // C11 6.7.2.3-3
            declareTag();
            return returnType(mtype);
        }

        /* A redeclaration only happens if both declarations are in
         * the same scope
         */
        const bool redeclar = (scopesym == sc2.inner().scopesym);

        if (redeclar)
        {
            if (mtype.tok == TOK.enum_ && s.isEnumDeclaration())
            {
                auto ed = s.isEnumDeclaration();
                if (mtype.members && ed.members)
                    .error(mtype.loc, "`%s` already has members", mtype.id.toChars());
                else if (!ed.members)
                {
                    ed.members = mtype.members;
                }
                else
                {
                }
                mtype.resolved = ed.type;
            }
            else if (mtype.tok == TOK.union_ && s.isUnionDeclaration() ||
                     mtype.tok == TOK.struct_ && s.isStructDeclaration())
            {
                // Add members to original declaration
                auto sd = s.isStructDeclaration();
                if (mtype.members && sd.members)
                {
                    /* struct S { int b; };
                     * struct S { int a; } *s;
                     */
                    .error(mtype.loc, "`%s` already has members", mtype.id.toChars());
                }
                else if (!sd.members)
                {
                    /* struct S;
                     * struct S { int a; } *s;
                     */
                    sd.members = mtype.members;
                    if (sd.semanticRun == PASS.semanticdone)
                    {
                        /* The first semantic pass marked `sd` as an opaque struct.
                         * Re-run semantic so that all newly assigned members are
                         * picked up and added to the symtab.
                         */
                        sd.semanticRun = PASS.semantic;
                        sd.dsymbolSemantic(sc2);
                    }
                }
                else
                {
                    /* struct S { int a; };
                     * struct S* s;
                     */
                }
                mtype.resolved = sd.type;
            }
            else
            {
                /* int S;
                 * struct S { int a; } *s;
                 */
                .error(mtype.loc, "redeclaration of `%s`", mtype.id.toChars());
                mtype.resolved = error();
            }
        }
        else if (mtype.members)
        {
            /* struct S;
             * { struct S { int a; } *s; }
             */
            declareTag();
        }
        else
        {
            if (mtype.tok == TOK.enum_ && s.isEnumDeclaration())
            {
                mtype.resolved = s.isEnumDeclaration().type;
            }
            else if (mtype.tok == TOK.union_ && s.isUnionDeclaration() ||
                     mtype.tok == TOK.struct_ && s.isStructDeclaration())
            {
                /* struct S;
                 * { struct S* s; }
                 */
                mtype.resolved = s.isStructDeclaration().type;
            }
            else
            {
                /* union S;
                 * { struct S* s; }
                 */
                .error(mtype.loc, "redeclaring `%s %s` as `%s %s`",
                    s.kind(), s.toChars(), Token.toChars(mtype.tok), mtype.id.toChars());
                declareTag();
            }
        }
        return returnType(mtype);
    }

    switch (type.ty)
    {
        default:         return visitType(type);
        case Tcomplex32:
        case Tcomplex64:
        case Tcomplex80: return visitComplex(type.isTypeBasic());
        case Tvector:    return visitVector(type.isTypeVector());
        case Tsarray:    return visitSArray(type.isTypeSArray());
        case Tarray:     return visitDArray(type.isTypeDArray());
        case Taarray:    return visitAArray(type.isTypeAArray());
        case Tpointer:   return visitPointer(type.isTypePointer());
        case Treference: return visitReference(type.isTypeReference());
        case Tfunction:  return visitFunction(type.isTypeFunction());
        case Tdelegate:  return visitDelegate(type.isTypeDelegate());
        case Tident:     return visitIdentifier(type.isTypeIdentifier());
        case Tinstance:  return visitInstance(type.isTypeInstance());
        case Ttypeof:    return visitTypeof(type.isTypeTypeof());
        case Ttraits:    return visitTraits(type.isTypeTraits());
        case Treturn:    return visitReturn(type.isTypeReturn());
        case Tstruct:    return visitStruct(type.isTypeStruct());
        case Tenum:      return visitEnum(type.isTypeEnum());
        case Tclass:     return visitClass(type.isTypeClass());
        case Ttuple:     return visitTuple(type.isTypeTuple());
        case Tslice:     return visitSlice(type.isTypeSlice());
        case Tmixin:     return visitMixin(type.isTypeMixin());
        case Ttag:       return visitTag(type.isTypeTag());
    }
}

Type trySemantic(Type type, Loc loc, Scope* sc)
{
    //printf("+trySemantic(%s) %d\n", toChars(), global.errors);

    // Needed to display any deprecations that were gagged
    auto tcopy = type.syntaxCopy();

    const errors = global.startGagging();
    Type t = typeSemantic(type, loc, sc);
    if (global.endGagging(errors) || t.ty == Terror) // if any errors happened
    {
        t = null;
    }
    else
    {
        // If `typeSemantic` succeeded, there may have been deprecations that
        // were gagged due the `startGagging` above.  Run again to display
        // those deprecations.  https://issues.dlang.org/show_bug.cgi?id=19107
        if (global.gaggedWarnings > 0)
            typeSemantic(tcopy, loc, sc);
    }
    //printf("-trySemantic(%s) %d\n", toChars(), global.errors);
    return t;
}

/************************************
 * If an identical type to `type` is in `type.stringtable`, return
 * the latter one. Otherwise, add it to `type.stringtable`.
 * Some types don't get merged and are returned as-is.
 * Params:
 *      type = Type to check against existing types
 * Returns:
 *      the type that was merged
 */
Type merge(Type type)
{
    switch (type.ty)
    {
        case Terror:
        case Ttypeof:
        case Tident:
        case Tinstance:
        case Tmixin:
        case Ttag:
            return type;        // don't merge placeholder types

        case Tsarray:
            // prevents generating the mangle if the array dim is not yet known
            if (!type.isTypeSArray().dim.isIntegerExp())
                return type;
            goto default;

        case Tenum:
            break;

        case Taarray:
            if (!type.isTypeAArray().index.merge().deco)
                return type;
            goto default;

        default:
            if (type.nextOf() && !type.nextOf().deco)
                return type;
            break;
    }

    //printf("merge(%s)\n", toChars());
    if (type.deco)
        return type;

    OutBuffer buf;
    buf.reserve(32);

    mangleToBuffer(type, buf);

    auto sv = type.stringtable.update(buf[]);
    if (sv.value)
    {
        Type t = sv.value;
        debug
        {
            import core.stdc.stdio;
            if (!t.deco)
                printf("t = %s\n", t.toChars());
        }
        assert(t.deco);
        //printf("old value, deco = '%s' %p\n", t.deco, t.deco);
        return t;
    }
    else
    {
        Type t = stripDefaultArgs(type);
        sv.value = t;
        type.deco = t.deco = cast(char*)sv.toDchars();
        //printf("new value, deco = '%s' %p\n", t.deco, t.deco);
        return t;
    }
}

/*************************************
 * This version does a merge even if the deco is already computed.
 * Necessary for types that have a deco, but are not merged.
 */
Type merge2(Type type)
{
    //printf("merge2(%s)\n", toChars());
    Type t = type;
    assert(t);
    if (!t.deco)
        return t.merge();

    auto sv = Type.stringtable.lookup(t.deco, strlen(t.deco));
    if (sv && sv.value)
    {
        t = sv.value;
        assert(t.deco);
    }
    else
        assert(0);
    return t;
}

/***************************************
 * Calculate built-in properties which just the type is necessary.
 *
 * Params:
 *  t = the type for which the property is calculated
 *  scope_ = the scope from which the property is being accessed. Used for visibility checks only.
 *  loc = the location where the property is encountered
 *  ident = the identifier of the property
 *  flag = if flag & 1, don't report "not a property" error and just return NULL.
 *  src = expression for type `t` or null.
 * Returns:
 *      expression representing the property, or null if not a property and (flag & 1)
 */
Expression getProperty(Type t, Scope* scope_, Loc loc, Identifier ident, int flag,
    Expression src = null)
{
    Expression visitType(Type mt)
    {
        Expression e;
        static if (LOGDOTEXP)
        {
            printf("Type::getProperty(type = '%s', ident = '%s')\n", mt.toChars(), ident.toChars());
        }
        if (ident == Id.__sizeof)
        {
            const sz = mt.size(loc);
            if (sz == SIZE_INVALID)
                return ErrorExp.get();
            return new IntegerExp(loc, sz, Type.tsize_t);
        }
        else if (ident == Id.__xalignof)
        {
            const explicitAlignment = mt.alignment();
            const naturalAlignment = mt.alignsize();
            const actualAlignment = (explicitAlignment.isDefault() ? naturalAlignment : explicitAlignment.get());
            return new IntegerExp(loc, actualAlignment, Type.tsize_t);
        }
        else if (ident == Id._init)
        {
            Type tb = mt.toBasetype();
            e = mt.defaultInitLiteral(loc);
            if (tb.ty == Tstruct && tb.needsNested())
            {
                e.isStructLiteralExp().useStaticInit = true;
            }
            return e;
        }
        else if (ident == Id._mangleof)
        {
            if (!mt.deco)
            {
                error(loc, "forward reference of type `%s.mangleof`", mt.toChars());
                return ErrorExp.get();
            }
            else
            {
                e = new StringExp(loc, mt.deco.toDString());
                Scope sc;
                sc.eSink = global.errorSink;
                e = e.expressionSemantic(&sc);
            }
            return e;
        }
        else if (ident == Id.stringof)
        {
            const s = mt.toChars();
            e = new StringExp(loc, s.toDString());
            Scope sc;
            sc.eSink = global.errorSink;
            e = e.expressionSemantic(&sc);
            return e;
        }
        else if (flag && mt != Type.terror)
        {
            return null;
        }

        Dsymbol s = null;
        if (mt.ty == Tstruct || mt.ty == Tclass || mt.ty == Tenum)
            s = mt.toDsymbol(null);
        if (s)
            s = s.search_correct(ident);
        if (s && !symbolIsVisible(scope_, s))
            s = null;

        if (mt == Type.terror)
            return ErrorExp.get();

        if (s)
            error(loc, "no property `%s` for type `%s`, did you mean `%s`?", ident.toChars(), mt.toChars(), s.toPrettyChars());
        else if (ident == Id.opCall && mt.ty == Tclass)
            error(loc, "no property `%s` for type `%s`, did you mean `new %s`?", ident.toChars(), mt.toChars(), mt.toPrettyChars());

        else if (const n = importHint(ident.toString()))
                error(loc, "no property `%s` for type `%s`, perhaps `import %.*s;` is needed?", ident.toChars(), mt.toChars(), cast(int)n.length, n.ptr);
        else
        {
            if (src)
            {
                error(loc, "no property `%s` for `%s` of type `%s`",
                    ident.toChars(), src.toChars(), mt.toPrettyChars(true));
                auto s2 = scope_.search_correct(ident);
                // UFCS
                if (s2 && s2.isFuncDeclaration)
                    errorSupplemental(loc, "did you mean %s `%s`?",
                        s2.kind(), s2.toChars());
                else if (src.type.ty == Tpointer)
                {
                    // structPtr.field
                    auto tn = (cast(TypeNext) src.type).nextOf();
                    if (auto as = tn.isAggregate())
                    {
                        if (auto s3 = as.search_correct(ident))
                        {
                            errorSupplemental(loc, "did you mean %s `%s`?",
                                s3.kind(), s3.toChars());
                        }
                    }
                }
            }
            else
                error(loc, "no property `%s` for type `%s`", ident.toChars(), mt.toPrettyChars(true));

            if (auto dsym = mt.toDsymbol(scope_))
            {
                if (auto sym = dsym.isAggregateDeclaration())
                {
                    if (!sym.members)
                    {
                        errorSupplemental(sym.loc, "`%s %s` is opaque and has no members.", sym.kind, mt.toPrettyChars(true));
                        return ErrorExp.get();
                    }

                    if (auto fd = search_function(sym, Id.opDispatch))
                    {
                        if (auto td = fd.isTemplateDeclaration())
                        {
                            e = mt.defaultInitLiteral(loc);
                            auto se = new StringExp(e.loc, ident.toString());
                            auto tiargs = new Objects();
                            tiargs.push(se);
                            auto dti = new DotTemplateInstanceExp(e.loc, e, Id.opDispatch, tiargs);
                            dti.ti.tempdecl = td;
                            dti.dotTemplateSemanticProp(scope_, DotExpFlag.none);
                            return ErrorExp.get();
                        }
                    }
                }
                errorSupplemental(dsym.loc, "%s `%s` defined here",
                    dsym.kind, dsym.toChars());
            }
        }

        return ErrorExp.get();
    }

    Expression visitError(TypeError)
    {
        return ErrorExp.get();
    }

    Expression visitBasic(TypeBasic mt)
    {
        Expression integerValue(dinteger_t i)
        {
            return new IntegerExp(loc, i, mt);
        }

        Expression intValue(dinteger_t i)
        {
            return new IntegerExp(loc, i, Type.tint32);
        }

        Expression floatValue(real_t r)
        {
            if (mt.isReal() || mt.isImaginary())
                return new RealExp(loc, r, mt);
            else
            {
                return new ComplexExp(loc, complex_t(r, r), mt);
            }
        }

        //printf("TypeBasic::getProperty('%s')\n", ident.toChars());
        if (ident == Id.max)
        {
            switch (mt.ty)
            {
            case Tint8:        return integerValue(byte.max);
            case Tuns8:        return integerValue(ubyte.max);
            case Tint16:       return integerValue(short.max);
            case Tuns16:       return integerValue(ushort.max);
            case Tint32:       return integerValue(int.max);
            case Tuns32:       return integerValue(uint.max);
            case Tint64:       return integerValue(long.max);
            case Tuns64:       return integerValue(ulong.max);
            case Tbool:        return integerValue(bool.max);
            case Tchar:        return integerValue(char.max);
            case Twchar:       return integerValue(wchar.max);
            case Tdchar:       return integerValue(dchar.max);
            case Tcomplex32:
            case Timaginary32:
            case Tfloat32:     return floatValue(target.FloatProperties.max);
            case Tcomplex64:
            case Timaginary64:
            case Tfloat64:     return floatValue(target.DoubleProperties.max);
            case Tcomplex80:
            case Timaginary80:
            case Tfloat80:     return floatValue(target.RealProperties.max);
            default:           break;
            }
        }
        else if (ident == Id.min)
        {
            switch (mt.ty)
            {
            case Tint8:        return integerValue(byte.min);
            case Tuns8:
            case Tuns16:
            case Tuns32:
            case Tuns64:
            case Tbool:
            case Tchar:
            case Twchar:
            case Tdchar:       return integerValue(0);
            case Tint16:       return integerValue(short.min);
            case Tint32:       return integerValue(int.min);
            case Tint64:       return integerValue(long.min);
            default:           break;
            }
        }
        else if (ident == Id.min_normal)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Timaginary32:
            case Tfloat32:     return floatValue(target.FloatProperties.min_normal);
            case Tcomplex64:
            case Timaginary64:
            case Tfloat64:     return floatValue(target.DoubleProperties.min_normal);
            case Tcomplex80:
            case Timaginary80:
            case Tfloat80:     return floatValue(target.RealProperties.min_normal);
            default:           break;
            }
        }
        else if (ident == Id.nan)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Tcomplex64:
            case Tcomplex80:
            case Timaginary32:
            case Timaginary64:
            case Timaginary80:
            case Tfloat32:
            case Tfloat64:
            case Tfloat80:     return floatValue(target.RealProperties.nan);
            default:           break;
            }
        }
        else if (ident == Id.infinity)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Tcomplex64:
            case Tcomplex80:
            case Timaginary32:
            case Timaginary64:
            case Timaginary80:
            case Tfloat32:
            case Tfloat64:
            case Tfloat80:     return floatValue(target.RealProperties.infinity);
            default:           break;
            }
        }
        else if (ident == Id.dig)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Timaginary32:
            case Tfloat32:     return intValue(target.FloatProperties.dig);
            case Tcomplex64:
            case Timaginary64:
            case Tfloat64:     return intValue(target.DoubleProperties.dig);
            case Tcomplex80:
            case Timaginary80:
            case Tfloat80:     return intValue(target.RealProperties.dig);
            default:           break;
            }
        }
        else if (ident == Id.epsilon)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Timaginary32:
            case Tfloat32:     return floatValue(target.FloatProperties.epsilon);
            case Tcomplex64:
            case Timaginary64:
            case Tfloat64:     return floatValue(target.DoubleProperties.epsilon);
            case Tcomplex80:
            case Timaginary80:
            case Tfloat80:     return floatValue(target.RealProperties.epsilon);
            default:           break;
            }
        }
        else if (ident == Id.mant_dig)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Timaginary32:
            case Tfloat32:     return intValue(target.FloatProperties.mant_dig);
            case Tcomplex64:
            case Timaginary64:
            case Tfloat64:     return intValue(target.DoubleProperties.mant_dig);
            case Tcomplex80:
            case Timaginary80:
            case Tfloat80:     return intValue(target.RealProperties.mant_dig);
            default:           break;
            }
        }
        else if (ident == Id.max_10_exp)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Timaginary32:
            case Tfloat32:     return intValue(target.FloatProperties.max_10_exp);
            case Tcomplex64:
            case Timaginary64:
            case Tfloat64:     return intValue(target.DoubleProperties.max_10_exp);
            case Tcomplex80:
            case Timaginary80:
            case Tfloat80:     return intValue(target.RealProperties.max_10_exp);
            default:           break;
            }
        }
        else if (ident == Id.max_exp)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Timaginary32:
            case Tfloat32:     return intValue(target.FloatProperties.max_exp);
            case Tcomplex64:
            case Timaginary64:
            case Tfloat64:     return intValue(target.DoubleProperties.max_exp);
            case Tcomplex80:
            case Timaginary80:
            case Tfloat80:     return intValue(target.RealProperties.max_exp);
            default:           break;
            }
        }
        else if (ident == Id.min_10_exp)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Timaginary32:
            case Tfloat32:     return intValue(target.FloatProperties.min_10_exp);
            case Tcomplex64:
            case Timaginary64:
            case Tfloat64:     return intValue(target.DoubleProperties.min_10_exp);
            case Tcomplex80:
            case Timaginary80:
            case Tfloat80:     return intValue(target.RealProperties.min_10_exp);
            default:           break;
            }
        }
        else if (ident == Id.min_exp)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
            case Timaginary32:
            case Tfloat32:     return intValue(target.FloatProperties.min_exp);
            case Tcomplex64:
            case Timaginary64:
            case Tfloat64:     return intValue(target.DoubleProperties.min_exp);
            case Tcomplex80:
            case Timaginary80:
            case Tfloat80:     return intValue(target.RealProperties.min_exp);
            default:           break;
            }
        }
        return visitType(mt);
    }

    Expression visitVector(TypeVector mt)
    {
        return visitType(mt);
    }

    Expression visitEnum(TypeEnum mt)
    {
        Expression e;
        if (ident == Id.max || ident == Id.min)
        {
            return mt.sym.getMaxMinValue(loc, ident);
        }
        else if (ident == Id._init)
        {
            e = mt.defaultInitLiteral(loc);
        }
        else if (ident == Id.stringof)
        {
            e = new StringExp(loc, mt.toString());
            Scope sc;
            e = e.expressionSemantic(&sc);
        }
        else if (ident == Id._mangleof)
        {
            e = visitType(mt);
        }
        else
        {
            e = mt.toBasetype().getProperty(scope_, loc, ident, flag);
        }
        return e;
    }

    Expression visitTuple(TypeTuple mt)
    {
        Expression e;
        static if (LOGDOTEXP)
        {
            printf("TypeTuple::getProperty(type = '%s', ident = '%s')\n", mt.toChars(), ident.toChars());
        }
        if (ident == Id.length)
        {
            e = new IntegerExp(loc, mt.arguments.length, Type.tsize_t);
        }
        else if (ident == Id._init)
        {
            e = mt.defaultInitLiteral(loc);
        }
        else if (flag)
        {
            e = null;
        }
        else
        {
            error(loc, "no property `%s` for sequence `%s`", ident.toChars(), mt.toChars());
            e = ErrorExp.get();
        }
        return e;
    }

    switch (t.ty)
    {
        default:        return t.isTypeBasic() ?
                                visitBasic(cast(TypeBasic)t) :
                                visitType(t);

        case Terror:    return visitError (t.isTypeError());
        case Tvector:   return visitVector(t.isTypeVector());
        case Tenum:     return visitEnum  (t.isTypeEnum());
        case Ttuple:    return visitTuple (t.isTypeTuple());
    }
}

/***************************************
 * Determine if Expression `exp` should instead be a Type, a Dsymbol, or remain an Expression.
 * Params:
 *      exp = Expression to look at
 *      t = if exp should be a Type, set t to that Type else null
 *      s = if exp should be a Dsymbol, set s to that Dsymbol else null
 *      e = if exp should remain an Expression, set e to that Expression else null
 *
 */
private void resolveExp(Expression exp, out Type t, out Expression e, out Dsymbol s)
{
    if (exp.isTypeExp())
        t = exp.type;
    else if (auto ve = exp.isVarExp())
    {
        if (auto v = ve.var.isVarDeclaration())
            e = exp;
        else
            s = ve.var;
    }
    else if (auto te = exp.isTemplateExp())
        s = te.td;
    else if (auto se = exp.isScopeExp())
        s = se.sds;
    else if (exp.isFuncExp())
        s = getDsymbol(exp);
    else if (auto dte = exp.isDotTemplateExp())
        s = dte.td;
    else if (exp.isErrorExp())
        t = Type.terror;
    else
        e = exp;
}

/************************************
 * Resolve type 'mt' to either type, symbol, or expression.
 * If errors happened, resolved to Type.terror.
 *
 * Params:
 *  mt = type to be resolved
 *  loc = the location where the type is encountered
 *  sc = the scope of the type
 *  pe = is set if t is an expression
 *  pt = is set if t is a type
 *  ps = is set if t is a symbol
 *  intypeid = true if in type id
 */
void resolve(Type mt, Loc loc, Scope* sc, out Expression pe, out Type pt, out Dsymbol ps, bool intypeid = false)
{
    void returnExp(Expression e)
    {
        pe = e;
        pt = null;
        ps = null;
    }

    void returnType(Type t)
    {
        pe = null;
        pt = t;
        ps = null;
    }

    void returnSymbol(Dsymbol s)
    {
        pe = null;
        pt = null;
        ps = s;
    }

    void returnError()
    {
        returnType(Type.terror);
    }

    void visitType(Type mt)
    {
        //printf("Type::resolve() %s, %d\n", mt.toChars(), mt.ty);
        Type t = typeSemantic(mt, loc, sc);
        assert(t);
        returnType(t);
    }

    void visitSArray(TypeSArray mt)
    {
        //printf("TypeSArray::resolve() %s\n", mt.toChars());
        mt.next.resolve(loc, sc, pe, pt, ps, intypeid);
        //printf("s = %p, e = %p, t = %p\n", ps, pe, pt);
        if (pe)
        {
            // It's really an index expression
            if (Dsymbol s = getDsymbol(pe))
                pe = new DsymbolExp(loc, s);
            returnExp(new ArrayExp(loc, pe, mt.dim));
        }
        else if (ps)
        {
            Dsymbol s = ps;
            if (auto tup = s.isTupleDeclaration())
            {
                mt.dim = semanticLength(sc, tup, mt.dim);
                mt.dim = mt.dim.ctfeInterpret();
                if (mt.dim.op == EXP.error)
                    return returnError();

                const d = mt.dim.toUInteger();
                if (d >= tup.objects.length)
                {
                    error(loc, "sequence index `%llu` out of bounds `[0 .. %llu]`", d, cast(ulong) tup.objects.length);
                    return returnError();
                }

                RootObject o = (*tup.objects)[cast(size_t)d];
                switch (o.dyncast()) with (DYNCAST)
                {
                case dsymbol:
                    return returnSymbol(cast(Dsymbol)o);
                case expression:
                    Expression e = cast(Expression)o;
                    if (e.op == EXP.dSymbol)
                        return returnSymbol(e.isDsymbolExp().s);
                    else
                        return returnExp(e);
                case type:
                    return returnType((cast(Type)o).addMod(mt.mod));
                default:
                    break;
                }

                /* Create a new TupleDeclaration which
                 * is a slice [d..d+1] out of the old one.
                 * Do it this way because TemplateInstance::semanticTiargs()
                 * can handle unresolved Objects this way.
                 */
                auto objects = new Objects(1);
                (*objects)[0] = o;
                return returnSymbol(new TupleDeclaration(loc, tup.ident, objects));
            }
            else
                return visitType(mt);
        }
        else
        {
            if (pt.ty != Terror)
                mt.next = pt; // prevent re-running semantic() on 'next'
            visitType(mt);
        }

    }

    void visitDArray(TypeDArray mt)
    {
        //printf("TypeDArray::resolve() %s\n", mt.toChars());
        mt.next.resolve(loc, sc, pe, pt, ps, intypeid);
        //printf("s = %p, e = %p, t = %p\n", ps, pe, pt);
        if (pe)
        {
            // It's really a slice expression
            if (Dsymbol s = getDsymbol(pe))
                pe = new DsymbolExp(loc, s);
            returnExp(new ArrayExp(loc, pe));
        }
        else if (ps)
        {
            if (auto tup = ps.isTupleDeclaration())
            {
                // keep ps
            }
            else
                visitType(mt);
        }
        else
        {
            if (pt.ty != Terror)
                mt.next = pt; // prevent re-running semantic() on 'next'
            visitType(mt);
        }
    }

    void visitAArray(TypeAArray mt)
    {
        //printf("TypeAArray::resolve() %s\n", mt.toChars());
        // Deal with the case where we thought the index was a type, but
        // in reality it was an expression.
        if (mt.index.ty == Tident || mt.index.ty == Tinstance || mt.index.ty == Tsarray)
        {
            Expression e;
            Type t;
            Dsymbol s;
            mt.index.resolve(loc, sc, e, t, s, intypeid);
            if (e)
            {
                // It was an expression -
                // Rewrite as a static array
                auto tsa = new TypeSArray(mt.next, e);
                tsa.mod = mt.mod; // just copy mod field so tsa's semantic is not yet done
                return tsa.resolve(loc, sc, pe, pt, ps, intypeid);
            }
            else if (t)
                mt.index = t;
            else
                .error(loc, "index is not a type or an expression");
        }
        visitType(mt);
    }

    /*************************************
     * Takes an array of Identifiers and figures out if
     * it represents a Type or an Expression.
     * Output:
     *      if expression, pe is set
     *      if type, pt is set
     */
    void visitIdentifier(TypeIdentifier mt)
    {
        //printf("TypeIdentifier::resolve(sc = %p, idents = '%s')\n", sc, mt.toChars());
        if (mt.ident == Id.ctfe)
        {
            error(loc, "variable `__ctfe` cannot be read at compile time");
            return returnError();
        }
        if (mt.ident == Id.builtin_va_list) // gcc has __builtin_va_xxxx for stdarg.h
        {
            /* Since we don't support __builtin_va_start, -arg, -end, we don't
             * have to actually care what -list is. A void* will do.
             * If we ever do care, import core.stdc.stdarg and pull
             * the definition out of that, similarly to how std.math is handled for PowExp
             */
            pt = target.va_listType(loc, sc);
            return;
        }

        Dsymbol scopesym;
        Dsymbol s = sc.search(loc, mt.ident, scopesym);
        /*
         * https://issues.dlang.org/show_bug.cgi?id=1170
         * https://issues.dlang.org/show_bug.cgi?id=10739
         *
         * If a symbol is not found, it might be declared in
         * a mixin-ed string or a mixin-ed template, so before
         * issuing an error semantically analyze all string/template
         * mixins that are members of the current ScopeDsymbol.
         */
        if (!s && sc.enclosing)
        {
            ScopeDsymbol sds = sc.enclosing.scopesym;
            if (sds && sds.members)
            {
                void semanticOnMixin(Dsymbol member)
                {
                    if (auto compileDecl = member.isMixinDeclaration())
                        compileDecl.dsymbolSemantic(sc);
                    else if (auto mixinTempl = member.isTemplateMixin())
                        mixinTempl.dsymbolSemantic(sc);
                }
                sds.members.foreachDsymbol( s => semanticOnMixin(s) );
                s = sc.search(loc, mt.ident, scopesym);
            }
        }

        if (s)
        {
            // https://issues.dlang.org/show_bug.cgi?id=16042
            // If `f` is really a function template, then replace `f`
            // with the function template declaration.
            if (auto f = s.isFuncDeclaration())
            {
                if (auto td = getFuncTemplateDecl(f))
                {
                    // If not at the beginning of the overloaded list of
                    // `TemplateDeclaration`s, then get the beginning
                    if (td.overroot)
                        td = td.overroot;
                    s = td;
                }
            }
        }

        mt.resolveHelper(loc, sc, s, scopesym, pe, pt, ps, intypeid);
        if (pt)
            pt = pt.addMod(mt.mod);
    }

    void visitInstance(TypeInstance mt)
    {
        // Note close similarity to TypeIdentifier::resolve()

        //printf("TypeInstance::resolve(sc = %p, tempinst = '%s')\n", sc, mt.tempinst.toChars());
        mt.tempinst.dsymbolSemantic(sc);
        if (!global.gag && mt.tempinst.errors)
            return returnError();

        mt.resolveHelper(loc, sc, mt.tempinst, null, pe, pt, ps, intypeid);
        if (pt)
            pt = pt.addMod(mt.mod);
        //if (pt) printf("pt = %d '%s'\n", pt.ty, pt.toChars());
    }

    void visitTypeof(TypeTypeof mt)
    {
        //printf("TypeTypeof::resolve(this = %p, sc = %p, idents = '%s')\n", mt, sc, mt.toChars());
        //static int nest; if (++nest == 50) *(char*)0=0;
        if (sc is null)
        {
            error(loc, "invalid scope");
            return returnError();
        }
        if (mt.inuse)
        {
            mt.inuse = 2;
            error(loc, "circular `typeof` definition");
        Lerr:
            mt.inuse--;
            return returnError();
        }
        mt.inuse++;

        /* Currently we cannot evaluate 'exp' in speculative context, because
         * the type implementation may leak to the final execution. Consider:
         *
         * struct S(T) {
         *   string toString() const { return "x"; }
         * }
         * void main() {
         *   alias X = typeof(S!int());
         *   assert(typeid(X).toString() == "x");
         * }
         */
        Scope* sc2 = sc.push();

        if (!mt.exp.isTypeidExp())
            /* Treat typeof(typeid(exp)) as needing
             * the full semantic analysis of the typeid.
             * https://issues.dlang.org/show_bug.cgi?id=20958
             */
            sc2.intypeof = 1;

        auto exp2 = mt.exp.expressionSemantic(sc2);
        exp2 = resolvePropertiesOnly(sc2, exp2);
        sc2.pop();

        if (exp2.op == EXP.error)
        {
            if (!global.gag)
                mt.exp = exp2;
            goto Lerr;
        }
        mt.exp = exp2;

        if ((mt.exp.op == EXP.type || mt.exp.op == EXP.scope_) &&
            // https://issues.dlang.org/show_bug.cgi?id=23863
            // compile time sequences are valid types
            !mt.exp.type.isTypeTuple())
        {
            if (!sc.inCfile && // in (extended) C typeof may be used on types as with sizeof
                mt.exp.checkType())
                goto Lerr;

            /* Today, 'typeof(func)' returns void if func is a
             * function template (TemplateExp), or
             * template lambda (FuncExp).
             * It's actually used in Phobos as an idiom, to branch code for
             * template functions.
             */
        }
        if (auto f = mt.exp.op == EXP.variable    ? mt.exp.isVarExp().var.isFuncDeclaration()
                   : mt.exp.op == EXP.dotVariable ? mt.exp.isDotVarExp().var.isFuncDeclaration() : null)
        {
            // f might be a unittest declaration which is incomplete when compiled
            // without -unittest. That causes a segfault in checkForwardRef, see
            // https://issues.dlang.org/show_bug.cgi?id=20626
            if ((!f.isUnitTestDeclaration() || global.params.useUnitTests) && checkForwardRef(f, loc))
                goto Lerr;
        }
        if (auto f = isFuncAddress(mt.exp))
        {
            if (checkForwardRef(f, loc))
                goto Lerr;
        }

        Type t = mt.exp.type;
        if (!t)
        {
            error(loc, "expression `%s` has no type", mt.exp.toChars());
            goto Lerr;
        }
        if (t.ty == Ttypeof)
        {
            error(loc, "forward reference to `%s`", mt.toChars());
            goto Lerr;
        }
        if (mt.idents.length == 0)
        {
            returnType(t.addMod(mt.mod));
        }
        else
        {
            if (Dsymbol s = t.toDsymbol(sc))
                mt.resolveHelper(loc, sc, s, null, pe, pt, ps, intypeid);
            else
            {
                auto e = typeToExpressionHelper(mt, new TypeExp(loc, t));
                e = e.expressionSemantic(sc);
                resolveExp(e, pt, pe, ps);
            }
            if (pt)
                pt = pt.addMod(mt.mod);
        }
        mt.inuse--;
    }

    void visitReturn(TypeReturn mt)
    {
        //printf("TypeReturn::resolve(sc = %p, idents = '%s')\n", sc, mt.toChars());
        Type t;
        {
            FuncDeclaration func = sc.func;
            if (!func)
            {
                error(loc, "`typeof(return)` must be inside function");
                return returnError();
            }
            if (func.fes)
                func = func.fes.func;
            t = func.type.nextOf();
            if (!t)
            {
                error(loc, "cannot use `typeof(return)` inside function `%s` with inferred return type", sc.func.toChars());
                return returnError();
            }
        }
        if (mt.idents.length == 0)
        {
            return returnType(t.addMod(mt.mod));
        }
        else
        {
            if (Dsymbol s = t.toDsymbol(sc))
                mt.resolveHelper(loc, sc, s, null, pe, pt, ps, intypeid);
            else
            {
                auto e = typeToExpressionHelper(mt, new TypeExp(loc, t));
                e = e.expressionSemantic(sc);
                resolveExp(e, pt, pe, ps);
            }
            if (pt)
                pt = pt.addMod(mt.mod);
        }
    }

    void visitSlice(TypeSlice mt)
    {
        mt.next.resolve(loc, sc, pe, pt, ps, intypeid);
        if (pe)
        {
            // It's really a slice expression
            if (Dsymbol s = getDsymbol(pe))
                pe = new DsymbolExp(loc, s);
            return returnExp(new ArrayExp(loc, pe, new IntervalExp(loc, mt.lwr, mt.upr)));
        }
        else if (ps)
        {
            Dsymbol s = ps;
            TupleDeclaration td = s.isTupleDeclaration();
            if (td)
            {
                /* It's a slice of a TupleDeclaration
                 */
                ScopeDsymbol sym = new ArrayScopeSymbol(sc, td);
                sym.parent = sc.scopesym;
                sc = sc.push(sym);
                sc = sc.startCTFE();
                mt.lwr = mt.lwr.expressionSemantic(sc);
                mt.upr = mt.upr.expressionSemantic(sc);
                sc = sc.endCTFE();
                sc = sc.pop();

                mt.lwr = mt.lwr.ctfeInterpret();
                mt.upr = mt.upr.ctfeInterpret();
                const i1 = mt.lwr.toUInteger();
                const i2 = mt.upr.toUInteger();
                if (!(i1 <= i2 && i2 <= td.objects.length))
                {
                    error(loc, "slice `[%llu..%llu]` is out of range of [0..%llu]", i1, i2, cast(ulong) td.objects.length);
                    return returnError();
                }

                if (i1 == 0 && i2 == td.objects.length)
                {
                    return returnSymbol(td);
                }

                /* Create a new TupleDeclaration which
                 * is a slice [i1..i2] out of the old one.
                 */
                auto objects = new Objects(cast(size_t)(i2 - i1));
                for (size_t i = 0; i < objects.length; i++)
                {
                    (*objects)[i] = (*td.objects)[cast(size_t)i1 + i];
                }

                return returnSymbol(new TupleDeclaration(loc, td.ident, objects));
            }
            else
                visitType(mt);
        }
        else
        {
            if (pt.ty != Terror)
                mt.next = pt; // prevent re-running semantic() on 'next'
            visitType(mt);
        }
    }

    void visitMixin(TypeMixin mt)
    {
        RootObject o = mt.obj;

        // if already resolved just set pe/pt/ps and return.
        if (o)
        {
            pe = o.isExpression();
            pt = o.isType();
            ps = o.isDsymbol();
            return;
        }

        o = mt.compileTypeMixin(loc, sc);
        if (auto t = o.isType())
        {
            resolve(t, loc, sc, pe, pt, ps, intypeid);
            if (pt)
                pt = pt.addMod(mt.mod);
        }
        else if (auto e = o.isExpression())
        {
            e = e.expressionSemantic(sc);
            if (auto et = e.isTypeExp())
                returnType(et.type.addMod(mt.mod));
            else
                returnExp(e);
        }
        else
            returnError();

        // save the result
        mt.obj = pe ? pe : (pt ? pt : ps);
    }

    void visitTraits(TypeTraits mt)
    {
        // if already resolved just return the cached object.
        if (mt.obj)
        {
            pt = mt.obj.isType();
            ps = mt.obj.isDsymbol();
            pe = mt.obj.isExpression();
            return;
        }

        import dmd.traits : semanticTraits;

        if (Expression e = semanticTraits(mt.exp, sc))
        {
            switch (e.op)
            {
            case EXP.dotVariable:
                mt.obj = e.isDotVarExp().var;
                break;
            case EXP.variable:
                mt.obj = e.isVarExp().var;
                break;
            case EXP.function_:
                auto fe = e.isFuncExp();
                mt.obj = fe.td ? fe.td : fe.fd;
                break;
            case EXP.dotTemplateDeclaration:
                mt.obj = e.isDotTemplateExp().td;
                break;
            case EXP.dSymbol:
                mt.obj = e.isDsymbolExp().s;
                break;
            case EXP.template_:
                mt.obj = e.isTemplateExp().td;
                break;
            case EXP.scope_:
                mt.obj = e.isScopeExp().sds;
                break;
            case EXP.tuple:
                TupleExp te = e.isTupleExp();
                Objects* elems = new Objects(te.exps.length);
                foreach (i; 0 .. elems.length)
                {
                    auto src = (*te.exps)[i];
                    switch (src.op)
                    {
                    case EXP.type:
                        (*elems)[i] = src.isTypeExp().type;
                        break;
                    case EXP.dotType:
                        (*elems)[i] = src.isDotTypeExp().sym.isType();
                        break;
                    case EXP.overloadSet:
                        (*elems)[i] = src.isOverExp().type;
                        break;
                    default:
                        if (auto sym = isDsymbol(src))
                            (*elems)[i] = sym;
                        else
                            (*elems)[i] = src;
                    }
                }
                TupleDeclaration td = new TupleDeclaration(e.loc, Identifier.generateId("__aliastup"), elems);
                mt.obj = td;
                break;
            case EXP.dotType:
                mt.obj = e.isDotTypeExp().sym.isType();
                break;
            case EXP.type:
                mt.obj = e.isTypeExp().type;
                break;
            case EXP.overloadSet:
                mt.obj = e.isOverExp().type;
                break;
            case EXP.error:
                break;
            default:
                mt.obj = e;
                break;
            }
        }

        if (mt.obj)
        {
            if (auto t = mt.obj.isType())
            {
                t = t.addMod(mt.mod);
                mt.obj = t;
                returnType(t);
            }
            else if (auto s = mt.obj.isDsymbol())
                returnSymbol(s);
            else if (auto e = mt.obj.isExpression())
                returnExp(e);
        }
        else
        {
            assert(global.errors);
            mt.obj = Type.terror;
            return returnError();
        }
    }

    switch (mt.ty)
    {
        default:        visitType      (mt);                    break;
        case Tsarray:   visitSArray    (mt.isTypeSArray());     break;
        case Tarray:    visitDArray    (mt.isTypeDArray());     break;
        case Taarray:   visitAArray    (mt.isTypeAArray());     break;
        case Tident:    visitIdentifier(mt.isTypeIdentifier()); break;
        case Tinstance: visitInstance  (mt.isTypeInstance());   break;
        case Ttypeof:   visitTypeof    (mt.isTypeTypeof());     break;
        case Treturn:   visitReturn    (mt.isTypeReturn());     break;
        case Tslice:    visitSlice     (mt.isTypeSlice());      break;
        case Tmixin:    visitMixin     (mt.isTypeMixin());      break;
        case Ttraits:   visitTraits    (mt.isTypeTraits());     break;
    }
}

/************************
 * Access the members of the object e. This type is same as e.type.
 * Params:
 *  mt = type for which the dot expression is used
 *  sc = instantiating scope
 *  e = expression to convert
 *  ident = identifier being used
 *  flag = DotExpFlag bit flags
 *
 * Returns:
 *  resulting expression with e.ident resolved
 */
Expression dotExp(Type mt, Scope* sc, Expression e, Identifier ident, DotExpFlag flag)
{
    enum LOGDOTEXP = false;
    if (LOGDOTEXP)
        printf("dotExp()\n");

    Expression visitType(Type mt)
    {
        VarDeclaration v = null;
        static if (LOGDOTEXP)
        {
            printf("Type::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        Expression ex = e.lastComma();
        if (ex.op == EXP.dotVariable)
        {
            DotVarExp dv = cast(DotVarExp)ex;
            v = dv.var.isVarDeclaration();
        }
        else if (ex.op == EXP.variable)
        {
            VarExp ve = cast(VarExp)ex;
            v = ve.var.isVarDeclaration();
        }
        if (v)
        {
            if (ident == Id.offsetof ||
                ident == Id.bitoffsetof ||
                ident == Id.bitwidth)
            {
                v.dsymbolSemantic(null);
                if (v.isField())
                {
                    auto ad = v.isMember();
                    objc.checkOffsetof(e, ad);
                    ad.size(e.loc);
                    if (ad.sizeok != Sizeok.done)
                        return ErrorExp.get();
                    uint value;
                    if (ident == Id.offsetof)
                        value = v.offset;
                    else // Id.bitoffsetof || Id.bitwidth
                    {
                        auto bf = v.isBitFieldDeclaration();
                        if (bf)
                        {
                            value = ident == Id.bitoffsetof ? bf.bitOffset : bf.fieldWidth;
                        }
                        else
                            error(v.loc, "`%s` is not a bitfield, cannot apply `%s`", v.toChars(), ident.toChars());
                    }
                    return new IntegerExp(e.loc, value, Type.tsize_t);
                }
            }
            else if (ident == Id._init)
            {
                Type tb = mt.toBasetype();
                e = mt.defaultInitLiteral(e.loc);
                if (tb.ty == Tstruct && tb.needsNested())
                {
                    e.isStructLiteralExp().useStaticInit = true;
                }
                goto Lreturn;
            }
        }
        if (ident == Id.stringof)
        {
            /* https://issues.dlang.org/show_bug.cgi?id=3796
             * this should demangle e.type.deco rather than
             * pretty-printing the type.
             */
            e = new StringExp(e.loc, e.toString());
        }
        else
            e = mt.getProperty(sc, e.loc, ident, flag & DotExpFlag.gag);

    Lreturn:
        if (e)
            e = e.expressionSemantic(sc);
        return e;
    }

    Expression visitError(TypeError)
    {
        return ErrorExp.get();
    }

    Expression visitBasic(TypeBasic mt)
    {
        static if (LOGDOTEXP)
        {
            printf("TypeBasic::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        Type t;
        if (ident == Id.re)
        {
            switch (mt.ty)
            {
            case Tcomplex32:
                t = mt.tfloat32;
                goto L1;

            case Tcomplex64:
                t = mt.tfloat64;
                goto L1;

            case Tcomplex80:
                t = mt.tfloat80;
                goto L1;
            L1:
                e = e.castTo(sc, t);
                break;

            case Tfloat32:
            case Tfloat64:
            case Tfloat80:
                break;

            case Timaginary32:
                t = mt.tfloat32;
                goto L2;

            case Timaginary64:
                t = mt.tfloat64;
                goto L2;

            case Timaginary80:
                t = mt.tfloat80;
                goto L2;
            L2:
                e = new RealExp(e.loc, CTFloat.zero, t);
                break;

            default:
                e = mt.Type.getProperty(sc, e.loc, ident, flag);
                break;
            }
        }
        else if (ident == Id.im)
        {
            Type t2;
            switch (mt.ty)
            {
            case Tcomplex32:
                t = mt.timaginary32;
                t2 = mt.tfloat32;
                goto L3;

            case Tcomplex64:
                t = mt.timaginary64;
                t2 = mt.tfloat64;
                goto L3;

            case Tcomplex80:
                t = mt.timaginary80;
                t2 = mt.tfloat80;
                goto L3;
            L3:
                e = e.castTo(sc, t);
                e.type = t2;
                break;

            case Timaginary32:
                t = mt.tfloat32;
                goto L4;

            case Timaginary64:
                t = mt.tfloat64;
                goto L4;

            case Timaginary80:
                t = mt.tfloat80;
                goto L4;
            L4:
                e = e.copy();
                e.type = t;
                break;

            case Tfloat32:
            case Tfloat64:
            case Tfloat80:
                e = new RealExp(e.loc, CTFloat.zero, mt);
                break;

            default:
                e = mt.Type.getProperty(sc, e.loc, ident, flag);
                break;
            }
        }
        else
        {
            return visitType(mt);
        }
        if (!(flag & 1) || e)
            e = e.expressionSemantic(sc);
        return e;
    }

    Expression visitVector(TypeVector mt)
    {
        static if (LOGDOTEXP)
        {
            printf("TypeVector::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        if (ident == Id.ptr && e.op == EXP.call)
        {
            /* The trouble with EXP.call is the return ABI for float[4] is different from
             * __vector(float[4]), and a type paint won't do.
             */
            e = new AddrExp(e.loc, e);
            e = e.expressionSemantic(sc);
            return e.castTo(sc, mt.basetype.nextOf().pointerTo());
        }
        if (ident == Id.array)
        {
            //e = e.castTo(sc, basetype);
            // Keep lvalue-ness
            e = new VectorArrayExp(e.loc, e);
            e = e.expressionSemantic(sc);
            return e;
        }
        if (ident == Id._init || ident == Id.offsetof || ident == Id.stringof || ident == Id.__xalignof)
        {
            // init should return a new VectorExp
            // https://issues.dlang.org/show_bug.cgi?id=12776
            // offsetof does not work on a cast expression, so use e directly
            // stringof should not add a cast to the output
            return visitType(mt);
        }

        // Properties based on the vector element type and are values of the element type
        if (ident == Id.max || ident == Id.min || ident == Id.min_normal ||
            ident == Id.nan || ident == Id.infinity || ident == Id.epsilon)
        {
            auto vet = mt.basetype.isTypeSArray().next; // vector element type
            if (auto ev = getProperty(vet, sc, e.loc, ident, DotExpFlag.gag))
                return ev.castTo(sc, mt); // 'broadcast' ev to the vector elements
        }

        return mt.basetype.dotExp(sc, e.castTo(sc, mt.basetype), ident, flag);
    }

    Expression visitArray(TypeArray mt)
    {
        static if (LOGDOTEXP)
        {
            printf("TypeArray::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }

        e = visitType(mt);

        if (!(flag & 1) || e)
            e = e.expressionSemantic(sc);
        return e;
    }

    Expression visitSArray(TypeSArray mt)
    {
        static if (LOGDOTEXP)
        {
            printf("TypeSArray::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        if (ident == Id.length)
        {
            Loc oldLoc = e.loc;
            e = mt.dim.copy();
            e.loc = oldLoc;
        }
        else if (ident == Id.ptr)
        {
            if (e.op == EXP.type)
            {
                error(e.loc, "`%s` is not an expression", e.toErrMsg());
                return ErrorExp.get();
            }
            else if (mt.dim.toUInteger() < 1 && checkUnsafeDotExp(sc, e, ident, flag))
            {
                // .ptr on static array is @safe unless size is 0
                // https://issues.dlang.org/show_bug.cgi?id=20853
                return ErrorExp.get();
            }
            e = e.castTo(sc, e.type.nextOf().pointerTo());
        }
        else if (ident == Id._tupleof)
        {
            if (e.isTypeExp())
            {
                error(e.loc, "`.tupleof` cannot be used on type `%s`", mt.toChars);
                return ErrorExp.get();
            }
            else
            {
                Expression e0;
                Expression ev = e;
                ev = extractSideEffect(sc, "__tup", e0, ev);

                const length = cast(size_t)mt.dim.toUInteger();
                auto exps = new Expressions();
                exps.reserve(length);
                foreach (i; 0 .. length)
                    exps.push(new IndexExp(e.loc, ev, new IntegerExp(e.loc, i, Type.tsize_t)));
                e = new TupleExp(e.loc, e0, exps);
            }
        }
        else
        {
            e = visitArray(mt);
        }
        if (!(flag & 1) || e)
            e = e.expressionSemantic(sc);
        return e;
    }

    Expression visitDArray(TypeDArray mt)
    {
        static if (LOGDOTEXP)
        {
            printf("TypeDArray::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        if (e.op == EXP.type && (ident == Id.length || ident == Id.ptr))
        {
            error(e.loc, "`%s` is not an expression", e.toErrMsg());
            return ErrorExp.get();
        }
        if (ident == Id.length)
        {
            if (e.op == EXP.string_)
            {
                StringExp se = cast(StringExp)e;
                return new IntegerExp(se.loc, se.len, Type.tsize_t);
            }
            if (e.op == EXP.null_)
            {
                return new IntegerExp(e.loc, 0, Type.tsize_t);
            }
            if (checkNonAssignmentArrayOp(e))
            {
                return ErrorExp.get();
            }
            e = new ArrayLengthExp(e.loc, e);
            e.type = Type.tsize_t;
            return e;
        }
        else if (ident == Id.ptr)
        {
            if (checkUnsafeDotExp(sc, e, ident, flag))
                return ErrorExp.get();
            return e.castTo(sc, mt.next.pointerTo());
        }
        else
        {
            return visitArray(mt);
        }
    }

    Expression visitAArray(TypeAArray mt)
    {
        static if (LOGDOTEXP)
        {
            printf("TypeAArray::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        if (ident == Id.length)
        {
            __gshared FuncDeclaration fd_aaLen = null;
            if (fd_aaLen is null)
            {
                auto fparams = new Parameters();
                fparams.push(new Parameter(Loc.initial, STC.const_ | STC.scope_, mt, null, null, null));
                fd_aaLen = FuncDeclaration.genCfunc(fparams, Type.tsize_t, Id.aaLen);
                TypeFunction tf = fd_aaLen.type.toTypeFunction();
                tf.purity = PURE.const_;
                tf.isNothrow = true;
                tf.isNogc = false;
            }
            Expression ev = new VarExp(e.loc, fd_aaLen, false);
            e = new CallExp(e.loc, ev, e);
            e.type = fd_aaLen.type.toTypeFunction().next;
            return e;
        }
        else
        {
            return visitType(mt);
        }
    }

    Expression visitReference(TypeReference mt)
    {
        static if (LOGDOTEXP)
        {
            printf("TypeReference::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        // References just forward things along
        return mt.next.dotExp(sc, e, ident, flag);
    }

    Expression visitDelegate(TypeDelegate mt)
    {
        static if (LOGDOTEXP)
        {
            printf("TypeDelegate::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        if (ident == Id.ptr)
        {
            e = new DelegatePtrExp(e.loc, e);
            e = e.expressionSemantic(sc);
        }
        else if (ident == Id.funcptr)
        {
            if (checkUnsafeDotExp(sc, e, ident, flag))
            {
                return ErrorExp.get();
            }
            e = new DelegateFuncptrExp(e.loc, e);
            e = e.expressionSemantic(sc);
        }
        else
        {
            return visitType(mt);
        }
        return e;
    }

    /***************************************
     * `ident` was not found as a member of `mt`.
     * Attempt to use overloaded opDispatch() or `alias this`.
     * If that fails, forward to visitType().
     * Params:
     *  mt = class or struct
     *  sc = context
     *  e = `this` for `ident`
     *  ident = name of member
     *  flag = flag & 1, don't report "not a property" error and just return NULL.
     *         flag & DotExpFlag.noAliasThis, don't do 'alias this' resolution.
     * Returns:
     *  resolved expression if found, otherwise null
     */
    Expression noMember(Type mt, Scope* sc, Expression e, Identifier ident, int flag)
    {
        //printf("Type.noMember(e: %s ident: %s flag: %d)\n", e.toChars(), ident.toChars(), flag);

        bool gagError = flag & 1;

        __gshared int nest;      // https://issues.dlang.org/show_bug.cgi?id=17380

        static Expression returnExp(Expression e)
        {
            --nest;
            return e;
        }

        if (++nest > global.recursionLimit)
        {
            .error(e.loc, "cannot resolve identifier `%s`", ident.toChars());
            return returnExp(gagError ? null : ErrorExp.get());
        }


        assert(mt.ty == Tstruct || mt.ty == Tclass);
        auto sym = mt.toDsymbol(sc).isAggregateDeclaration();
        assert(sym);
        if (// https://issues.dlang.org/show_bug.cgi?id=22054
            // if a class or struct does not have a body
            // there is no point in searching for its members
            sym.members &&
            ident != Id.__sizeof &&
            ident != Id.__xalignof &&
            ident != Id._init &&
            ident != Id._mangleof &&
            ident != Id.stringof &&
            ident != Id.offsetof &&
            ident != Id.bitoffsetof &&
            ident != Id.bitwidth &&
            // https://issues.dlang.org/show_bug.cgi?id=15045
            // Don't forward special built-in member functions.
            ident != Id.ctor &&
            ident != Id.dtor &&
            ident != Id.__xdtor &&
            ident != Id.postblit &&
            ident != Id.__xpostblit)
        {
            /* Look for overloaded opDispatch to see if we should forward request
             * to it.
             */
            if (auto fd = search_function(sym, Id.opDispatch))
            {
                /* Rewrite e.ident as:
                 *  e.opDispatch!("ident")
                 */
                TemplateDeclaration td = fd.isTemplateDeclaration();
                if (!td)
                {
                    .error(fd.loc, "%s `%s` must be a template `opDispatch(string s)`, not a %s", fd.kind, fd.toPrettyChars, fd.kind());
                    return returnExp(ErrorExp.get());
                }
                auto se = new StringExp(e.loc, ident.toString());
                auto tiargs = new Objects();
                tiargs.push(se);
                auto dti = new DotTemplateInstanceExp(e.loc, e, Id.opDispatch, tiargs);
                dti.ti.tempdecl = td;
                /* opDispatch, which doesn't need IFTI,  may occur instantiate error.
                 * e.g.
                 *  template opDispatch(name) if (isValid!name) { ... }
                 */
                const errors = gagError ? global.startGagging() : 0;
                e = dti.dotTemplateSemanticProp(sc, DotExpFlag.none);
                if (gagError && global.endGagging(errors))
                    e = null;
                return returnExp(e);
            }

            /* See if we should forward to the alias this.
             */
            auto alias_e = flag & DotExpFlag.noAliasThis ? null
                                                         : resolveAliasThis(sc, e, gagError);
            if (alias_e && alias_e != e)
            {
                /* Rewrite e.ident as:
                 *  e.aliasthis.ident
                 */
                auto die = new DotIdExp(e.loc, alias_e, ident);

                const errors = gagError ? 0 : global.startGagging();
                auto exp = die.dotIdSemanticProp(sc, gagError);
                if (!gagError)
                {
                    global.endGagging(errors);
                    if (exp && exp.op == EXP.error)
                        exp = null;
                }

                if (exp && gagError)
                    // now that we know that the alias this leads somewhere useful,
                    // go back and print deprecations/warnings that we skipped earlier due to the gag
                    resolveAliasThis(sc, e, false);

                return returnExp(exp);
            }
        }
        return returnExp(visitType(mt));
    }

    Expression visitStruct(TypeStruct mt)
    {
        Dsymbol s;
        static if (LOGDOTEXP)
        {
            printf("TypeStruct::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        assert(e.op != EXP.dot);

        // https://issues.dlang.org/show_bug.cgi?id=14010
        if (!sc.inCfile && ident == Id._mangleof)
        {
            return mt.getProperty(sc, e.loc, ident, flag & 1);
        }

        /* If e.tupleof
         */
        if (ident == Id._tupleof)
        {
            /* Create a TupleExp out of the fields of the struct e:
             * (e.field0, e.field1, e.field2, ...)
             */
            e = e.expressionSemantic(sc); // do this before turning on noAccessCheck

            if (!mt.sym.determineFields())
            {
                error(e.loc, "unable to determine fields of `%s` because of forward references", mt.toChars());
            }

            Expression e0;
            Expression ev = e.op == EXP.type ? null : e;
            if (ev)
                ev = extractSideEffect(sc, "__tup", e0, ev);

            auto exps = new Expressions();
            exps.reserve(mt.sym.fields.length);
            for (size_t i = 0; i < mt.sym.fields.length; i++)
            {
                VarDeclaration v = mt.sym.fields[i];
                Expression ex;
                if (ev)
                    ex = new DotVarExp(e.loc, ev, v);
                else
                {
                    ex = new VarExp(e.loc, v);
                    ex.type = ex.type.addMod(e.type.mod);
                }
                exps.push(ex);
            }

            e = new TupleExp(e.loc, e0, exps);
            Scope* sc2 = sc.push();
            sc2.noAccessCheck = true;
            e = e.expressionSemantic(sc2);
            sc2.pop();
            return e;
        }

        immutable flags = sc.ignoresymbolvisibility ? SearchOpt.ignoreVisibility : 0;
        s = mt.sym.search(e.loc, ident, flags | SearchOpt.ignorePrivateImports);
    L1:
        if (!s)
        {
            return noMember(mt, sc, e, ident, flag);
        }
        if (!sc.ignoresymbolvisibility && !symbolIsVisible(sc, s))
        {
            return noMember(mt, sc, e, ident, flag);
        }
        // check before alias resolution; the alias itself might be deprecated!
        if (auto ad = s.isAliasDeclaration)
        {
            s.checkDeprecated(e.loc, sc);

            // Fix for https://github.com/dlang/dmd/issues/20610
            if (ad.originalType)
            {
                if (auto tid = ad.originalType.isTypeIdentifier())
                {
                    if (tid.idents.length)
                    {
                        static if (0)
                        {
                            printf("TypeStruct::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
                            printf("AliasDeclaration: %s\n", ad.toChars());
                            if (ad.aliassym)
                                printf("aliassym: %s\n", ad.aliassym.toChars());
                            printf("tid type: %s\n", toChars(tid));
                        }
                        /* Rewrite e.s as e.(tid.ident).(tid.idents)
                         */
                        Expression die = new DotIdExp(e.loc, e, tid.ident);
                        foreach (id; tid.idents) // maybe use typeToExpressionHelper()
                            die = new DotIdExp(e.loc, die, cast(Identifier)id);
                        /* Ambiguous syntax, only way to disambiguate it to try it
                         */
                        die = dmd.expressionsem.trySemantic(die, sc);
                        if (die && die.isDotVarExp())   // shrink wrap around DotVarExp()
                        {
                            return die;
                        }
                    }
                }
            }
        }
        s = s.toAlias();

        if (auto em = s.isEnumMember())
        {
            return em.getVarExp(e.loc, sc);
        }
        if (auto v = s.isVarDeclaration())
        {
            v.checkDeprecated(e.loc, sc);
            v.checkDisabled(e.loc, sc);
            if (!v.type ||
                !v.type.deco && v.inuse)
            {
                if (v.inuse) // https://issues.dlang.org/show_bug.cgi?id=9494
                    error(e.loc, "circular reference to %s `%s`", v.kind(), v.toPrettyChars());
                else
                    error(e.loc, "forward reference to %s `%s`", v.kind(), v.toPrettyChars());
                return ErrorExp.get();
            }
            if (v.type.ty == Terror)
            {
                return ErrorExp.get();
            }

            if ((v.storage_class & STC.manifest) && v._init)
            {
                if (v.inuse)
                {
                    error(e.loc, "circular initialization of %s `%s`", v.kind(), v.toPrettyChars());
                    return ErrorExp.get();
                }
                checkAccess(e.loc, sc, null, v);
                Expression ve = new VarExp(e.loc, v);
                if (!isTrivialExp(e))
                {
                    ve = new CommaExp(e.loc, e, ve);
                }
                return ve.expressionSemantic(sc);
            }
        }

        if (auto t = s.getType())
        {
            return (new TypeExp(e.loc, t)).expressionSemantic(sc);
        }

        TemplateMixin tm = s.isTemplateMixin();
        if (tm)
        {
            return new DotExp(e.loc, e, new ScopeExp(e.loc, tm)).expressionSemantic(sc);
        }

        TemplateDeclaration td = s.isTemplateDeclaration();
        if (td)
        {
            if (e.op == EXP.type)
                e = new TemplateExp(e.loc, td);
            else
                e = new DotTemplateExp(e.loc, e, td);
            return e.expressionSemantic(sc);
        }

        TemplateInstance ti = s.isTemplateInstance();
        if (ti)
        {
            if (!ti.semanticRun)
            {
                ti.dsymbolSemantic(sc);
                if (!ti.inst || ti.errors) // if template failed to expand
                {
                    return ErrorExp.get();
                }
            }
            s = ti.inst.toAlias();
            if (!s.isTemplateInstance())
                goto L1;
            if (e.op == EXP.type)
                e = new ScopeExp(e.loc, ti);
            else
                e = new DotExp(e.loc, e, new ScopeExp(e.loc, ti));
            return e.expressionSemantic(sc);
        }

        if (s.isImport() || s.isModule() || s.isPackage())
        {
            return symbolToExp(s, e.loc, sc, false);
        }

        OverloadSet o = s.isOverloadSet();
        if (o)
        {
            auto oe = new OverExp(e.loc, o);
            if (e.op == EXP.type)
            {
                return oe;
            }
            return new DotExp(e.loc, e, oe);
        }

        Declaration d = s.isDeclaration();
        if (!d)
        {
            error(e.loc, "`%s.%s` is not a declaration", e.toErrMsg(), ident.toChars());
            return ErrorExp.get();
        }

        if (e.op == EXP.type)
        {
            /* It's:
             *    Struct.d
             */
            if (TupleDeclaration tup = d.isTupleDeclaration())
            {
                e = new TupleExp(e.loc, tup);
                return e.expressionSemantic(sc);
            }
            if (d.needThis() && sc.intypeof != 1)
            {
                /* Rewrite as:
                 *  this.d
                 *
                 * only if the scope in which we are
                 * has a `this` that matches the type
                 * of the lhs of the dot expression.
                 *
                 * https://issues.dlang.org/show_bug.cgi?id=23617
                 */
                auto fd = hasThis(sc);
                if (fd && fd.isThis() == mt.sym)
                {
                    e = new DotVarExp(e.loc, new ThisExp(e.loc), d);
                    return e.expressionSemantic(sc);
                }
            }
            if (d.semanticRun == PASS.initial)
                d.dsymbolSemantic(null);
            checkAccess(e.loc, sc, e, d);
            auto ve = new VarExp(e.loc, d);
            if (d.isVarDeclaration() && d.needThis())
                ve.type = d.type.addMod(e.type.mod);
            return ve;
        }

        bool unreal = e.op == EXP.variable && (cast(VarExp)e).var.isField();
        if (d.isDataseg() || unreal && d.isField())
        {
            // (e, d)
            checkAccess(e.loc, sc, e, d);
            Expression ve = new VarExp(e.loc, d);
            e = unreal ? ve : new CommaExp(e.loc, e, ve);
            return e.expressionSemantic(sc);
        }

        e = new DotVarExp(e.loc, e, d);
        return e.expressionSemantic(sc);
    }

    Expression visitEnum(TypeEnum mt)
    {
        static if (LOGDOTEXP)
        {
            printf("TypeEnum::dotExp(e = '%s', ident = '%s') '%s'\n", e.toChars(), ident.toChars(), mt.toChars());
        }
        // https://issues.dlang.org/show_bug.cgi?id=14010
        if (ident == Id._mangleof)
        {
            return mt.getProperty(sc, e.loc, ident, flag & 1);
        }

        if (mt.sym.semanticRun < PASS.semanticdone)
            mt.sym.dsymbolSemantic(null);

        Dsymbol s = mt.sym.search(e.loc, ident);
        if (!s)
        {
            if (ident == Id._init)
            {
                return mt.getProperty(sc, e.loc, ident, flag & 1);
            }

            /* Allow special enums to not need a member list
             */
            if ((ident == Id.max || ident == Id.min) && (mt.sym.members || !mt.sym.isSpecial()))
            {
                return mt.getProperty(sc, e.loc, ident, flag & 1);
            }

            Expression res = mt.sym.getMemtype(Loc.initial).dotExp(sc, e, ident, DotExpFlag.gag);
            if (!(flag & 1) && !res)
            {
                if (auto ns = mt.sym.search_correct(ident))
                    error(e.loc, "no property `%s` for type `%s`. Did you mean `%s.%s` ?", ident.toChars(), mt.toChars(), mt.toChars(),
                        ns.toChars());
                else
                    error(e.loc, "no property `%s` for type `%s`", ident.toChars(),
                        mt.toChars());

                errorSupplemental(mt.sym.loc, "%s `%s` defined here",
                    mt.sym.kind, mt.toChars());
                return ErrorExp.get();
            }
            return res;
        }
        EnumMember m = s.isEnumMember();
        return m.getVarExp(e.loc, sc);
    }

    Expression visitClass(TypeClass mt)
    {
        Dsymbol s;
        static if (LOGDOTEXP)
        {
            printf("TypeClass::dotExp(e = '%s', ident = '%s')\n", e.toChars(), ident.toChars());
        }
        assert(e.op != EXP.dot);

        // https://issues.dlang.org/show_bug.cgi?id=12543
        if (ident == Id.__sizeof || ident == Id.__xalignof || ident == Id._mangleof)
        {
            return mt.Type.getProperty(sc, e.loc, ident, 0);
        }

        /* If e.tupleof
         */
        if (ident == Id._tupleof)
        {
            objc.checkTupleof(e, mt);

            /* Create a TupleExp
             */
            e = e.expressionSemantic(sc); // do this before turning on noAccessCheck

            mt.sym.size(e.loc); // do semantic of type

            Expression e0;
            Expression ev = e.op == EXP.type ? null : e;
            if (ev)
                ev = extractSideEffect(sc, "__tup", e0, ev);

            auto exps = new Expressions();
            exps.reserve(mt.sym.fields.length);
            for (size_t i = 0; i < mt.sym.fields.length; i++)
            {
                VarDeclaration v = mt.sym.fields[i];
                // Don't include hidden 'this' pointer
                if (v.isThisDeclaration())
                    continue;
                Expression ex;
                if (ev)
                    ex = new DotVarExp(e.loc, ev, v);
                else
                {
                    ex = new VarExp(e.loc, v);
                    ex.type = ex.type.addMod(e.type.mod);
                }
                exps.push(ex);
            }

            e = new TupleExp(e.loc, e0, exps);
            Scope* sc2 = sc.push();
            sc2.noAccessCheck = true;
            e = e.expressionSemantic(sc2);
            sc2.pop();
            return e;
        }

        SearchOptFlags flags = sc.ignoresymbolvisibility ? SearchOpt.ignoreVisibility : SearchOpt.all;
        s = mt.sym.search(e.loc, ident, flags | SearchOpt.ignorePrivateImports);

    L1:
        if (!s)
        {
            // See if it's a 'this' class or a base class
            if (mt.sym.ident == ident)
            {
                if (e.op == EXP.type)
                {
                    return mt.Type.getProperty(sc, e.loc, ident, 0);
                }
                e = new DotTypeExp(e.loc, e, mt.sym);
                e = e.expressionSemantic(sc);
                return e;
            }
            if (auto cbase = mt.sym.searchBase(ident))
            {
                if (e.op == EXP.type)
                {
                    return mt.Type.getProperty(sc, e.loc, ident, 0);
                }
                if (auto ifbase = cbase.isInterfaceDeclaration())
                    e = new CastExp(e.loc, e, ifbase.type);
                else
                    e = new DotTypeExp(e.loc, e, cbase);
                e = e.expressionSemantic(sc);
                return e;
            }

            if (ident == Id.classinfo)
            {
                if (!Type.typeinfoclass)
                {
                    error(e.loc, "`object.TypeInfo_Class` could not be found, but is implicitly used");
                    return ErrorExp.get();
                }

                Type t = Type.typeinfoclass.type;
                if (e.op == EXP.type || e.op == EXP.dotType)
                {
                    /* For type.classinfo, we know the classinfo
                     * at compile time.
                     */
                    if (!mt.sym.vclassinfo)
                        mt.sym.vclassinfo = new TypeInfoClassDeclaration(mt.sym.type);
                    e = new VarExp(e.loc, mt.sym.vclassinfo);
                    e = e.addressOf();
                    e.type = t; // do this so we don't get redundant dereference
                }
                else
                {
                    /* For class objects, the classinfo reference is the first
                     * entry in the vtbl[]
                     */
                    e = new PtrExp(e.loc, e);
                    e.type = t.pointerTo();
                    if (mt.sym.isInterfaceDeclaration())
                    {
                        if (mt.sym.isCPPinterface())
                        {
                            /* C++ interface vtbl[]s are different in that the
                             * first entry is always pointer to the first virtual
                             * function, not classinfo.
                             * We can't get a .classinfo for it.
                             */
                            error(e.loc, "no `.classinfo` for C++ interface objects");
                        }
                        /* For an interface, the first entry in the vtbl[]
                         * is actually a pointer to an instance of struct Interface.
                         * The first member of Interface is the .classinfo,
                         * so add an extra pointer indirection.
                         */
                        e.type = e.type.pointerTo();
                        e = new PtrExp(e.loc, e);
                        e.type = t.pointerTo();
                    }
                    e = new PtrExp(e.loc, e, t);
                }
                return e;
            }

            if (ident == Id.__vptr)
            {
                /* The pointer to the vtbl[]
                 * *cast(immutable(void*)**)e
                 */
                e = e.castTo(sc, mt.tvoidptr.immutableOf().pointerTo().pointerTo());
                e = new PtrExp(e.loc, e);
                e = e.expressionSemantic(sc);
                return e;
            }

            if (ident == Id.__monitor && mt.sym.hasMonitor())
            {
                /* The handle to the monitor (call it a void*)
                 * *(cast(void**)e + 1)
                 */
                e = e.castTo(sc, mt.tvoidptr.pointerTo());
                e = new AddExp(e.loc, e, IntegerExp.literal!1);
                e = new PtrExp(e.loc, e);
                e = e.expressionSemantic(sc);
                return e;
            }

            if (ident == Id.outer && mt.sym.vthis)
            {
                if (mt.sym.vthis.semanticRun == PASS.initial)
                    mt.sym.vthis.dsymbolSemantic(null);

                if (auto cdp = mt.sym.toParentLocal().isClassDeclaration())
                {
                    auto dve = new DotVarExp(e.loc, e, mt.sym.vthis);
                    dve.type = cdp.type.addMod(e.type.mod);
                    return dve;
                }

                /* https://issues.dlang.org/show_bug.cgi?id=15839
                 * Find closest parent class through nested functions.
                 */
                for (auto p = mt.sym.toParentLocal(); p; p = p.toParentLocal())
                {
                    auto fd = p.isFuncDeclaration();
                    if (!fd)
                        break;
                    auto ad = fd.isThis();
                    if (!ad && fd.isNested())
                        continue;
                    if (!ad)
                        break;
                    if (auto cdp = ad.isClassDeclaration())
                    {
                        auto ve = new ThisExp(e.loc);

                        ve.var = fd.vthis;
                        const nestedError = fd.vthis.checkNestedReference(sc, e.loc);
                        assert(!nestedError);

                        ve.type = cdp.type.addMod(fd.vthis.type.mod).addMod(e.type.mod);
                        return ve;
                    }
                    break;
                }

                // Continue to show enclosing function's frame (stack or closure).
                auto dve = new DotVarExp(e.loc, e, mt.sym.vthis);
                dve.type = mt.sym.vthis.type.addMod(e.type.mod);
                return dve;
            }

            return noMember(mt, sc, e, ident, flag & 1);
        }
        if (!sc.ignoresymbolvisibility && !symbolIsVisible(sc, s))
        {
            return noMember(mt, sc, e, ident, flag);
        }
        if (!s.isFuncDeclaration()) // because of overloading
        {
            s.checkDeprecated(e.loc, sc);
            if (auto d = s.isDeclaration())
                d.checkDisabled(e.loc, sc);
        }
        s = s.toAlias();

        if (auto em = s.isEnumMember())
        {
            return em.getVarExp(e.loc, sc);
        }
        if (auto v = s.isVarDeclaration())
        {
            if (!v.type ||
                !v.type.deco && v.inuse)
            {
                if (v.inuse) // https://issues.dlang.org/show_bug.cgi?id=9494
                    error(e.loc, "circular reference to %s `%s`", v.kind(), v.toPrettyChars());
                else
                    error(e.loc, "forward reference to %s `%s`", v.kind(), v.toPrettyChars());
                return ErrorExp.get();
            }
            if (v.type.ty == Terror)
            {
                error(e.loc, "type of variable `%s` has errors", v.toPrettyChars);
                return ErrorExp.get();
            }

            if ((v.storage_class & STC.manifest) && v._init)
            {
                if (v.inuse)
                {
                    error(e.loc, "circular initialization of %s `%s`", v.kind(), v.toPrettyChars());
                    return ErrorExp.get();
                }
                checkAccess(e.loc, sc, null, v);
                Expression ve = new VarExp(e.loc, v);
                ve = ve.expressionSemantic(sc);
                return ve;
            }
        }

        if (auto t = s.getType())
        {
            return (new TypeExp(e.loc, t)).expressionSemantic(sc);
        }

        TemplateMixin tm = s.isTemplateMixin();
        if (tm)
        {
            return new DotExp(e.loc, e, new ScopeExp(e.loc, tm)).expressionSemantic(sc);
        }

        TemplateDeclaration td = s.isTemplateDeclaration();

        Expression toTemplateExp(TemplateDeclaration td)
        {
            if (e.op == EXP.type)
                e = new TemplateExp(e.loc, td);
            else
                e = new DotTemplateExp(e.loc, e, td);
            e = e.expressionSemantic(sc);
            return e;
        }

        if (td)
        {
            return toTemplateExp(td);
        }

        TemplateInstance ti = s.isTemplateInstance();
        if (ti)
        {
            if (!ti.semanticRun)
            {
                ti.dsymbolSemantic(sc);
                if (!ti.inst || ti.errors) // if template failed to expand
                {
                    return ErrorExp.get();
                }
            }
            s = ti.inst.toAlias();
            if (!s.isTemplateInstance())
                goto L1;
            if (e.op == EXP.type)
                e = new ScopeExp(e.loc, ti);
            else
                e = new DotExp(e.loc, e, new ScopeExp(e.loc, ti));
            return e.expressionSemantic(sc);
        }

        if (s.isImport() || s.isModule() || s.isPackage())
        {
            e = symbolToExp(s, e.loc, sc, false);
            return e;
        }

        OverloadSet o = s.isOverloadSet();
        if (o)
        {
            auto oe = new OverExp(e.loc, o);
            if (e.op == EXP.type)
            {
                return oe;
            }
            return new DotExp(e.loc, e, oe);
        }

        Declaration d = s.isDeclaration();
        if (!d)
        {
            error(e.loc, "`%s.%s` is not a declaration", e.toErrMsg(), ident.toChars());
            return ErrorExp.get();
        }

        if (e.op == EXP.type)
        {
            /* It's:
             *    Class.d
             */
            if (TupleDeclaration tup = d.isTupleDeclaration())
            {
                e = new TupleExp(e.loc, tup);
                e = e.expressionSemantic(sc);
                return e;
            }

            if (mt.sym.classKind == ClassKind.objc
                && d.isFuncDeclaration()
                && d.isFuncDeclaration().isStatic
                && d.isFuncDeclaration().objc.selector)
            {
                auto classRef = new ObjcClassReferenceExp(e.loc, mt.sym);
                classRef.type = objc.getRuntimeMetaclass(mt.sym).getType();
                return new DotVarExp(e.loc, classRef, d).expressionSemantic(sc);
            }
            else if (d.needThis() && sc.intypeof != 1)
            {
                /* Rewrite as:
                 *  this.d
                 */
                AggregateDeclaration ad = d.isMemberLocal();
                if (auto f = hasThis(sc))
                {
                    // This is almost same as getRightThis() in expressionsem.d
                    Expression e1;
                    Type t;
                    /* returns: true to continue, false to return */
                    if (f.hasDualContext())
                    {
                        if (f.followInstantiationContext(ad))
                        {
                            e1 = new VarExp(e.loc, f.vthis);
                            e1 = new PtrExp(e1.loc, e1);
                            e1 = new IndexExp(e1.loc, e1, IntegerExp.literal!1);
                            auto pd = f.toParent2().isDeclaration();
                            assert(pd);
                            t = pd.type.toBasetype();
                            e1 = getThisSkipNestedFuncs(e1.loc, sc, f.toParent2(), ad, e1, t, d, true);
                            if (!e1)
                            {
                                e = new VarExp(e.loc, d);
                                return e;
                            }
                            goto L2;
                        }
                    }
                    e1 = new ThisExp(e.loc);
                    e1 = e1.expressionSemantic(sc);
                L2:
                    t = e1.type.toBasetype();
                    ClassDeclaration cd = e.type.isClassHandle();
                    ClassDeclaration tcd = t.isClassHandle();
                    if (cd && tcd && (tcd == cd || cd.isBaseOf(tcd, null)))
                    {
                        e = new DotTypeExp(e1.loc, e1, cd);
                        e = new DotVarExp(e.loc, e, d);
                        e = e.expressionSemantic(sc);
                        return e;
                    }
                    if (tcd && tcd.isNested())
                    {
                        /* e1 is the 'this' pointer for an inner class: tcd.
                         * Rewrite it as the 'this' pointer for the outer class.
                         */
                        auto vthis = tcd.followInstantiationContext(ad) ? tcd.vthis2 : tcd.vthis;
                        e1 = new DotVarExp(e.loc, e1, vthis);
                        e1.type = vthis.type;
                        e1.type = e1.type.addMod(t.mod);
                        // Do not call ensureStaticLinkTo()
                        //e1 = e1.expressionSemantic(sc);

                        // Skip up over nested functions, and get the enclosing
                        // class type.
                        e1 = getThisSkipNestedFuncs(e1.loc, sc, tcd.toParentP(ad), ad, e1, t, d, true);
                        if (!e1)
                        {
                            e = new VarExp(e.loc, d);
                            return e;
                        }
                        goto L2;
                    }
                }
            }
            //printf("e = %s, d = %s\n", e.toChars(), d.toChars());
            if (d.semanticRun == PASS.initial)
                d.dsymbolSemantic(null);

            // If static function, get the most visible overload.
            // Later on the call is checked for correctness.
            // https://issues.dlang.org/show_bug.cgi?id=12511
            Dsymbol d2 = d;
            if (auto fd = d.isFuncDeclaration())
            {
                import dmd.access : mostVisibleOverload;
                d2 = mostVisibleOverload(fd, sc._module);
            }

            checkAccess(e.loc, sc, e, d2);
            if (d2.isDeclaration())
            {
                d = cast(Declaration)d2;
                auto ve = new VarExp(e.loc, d);
                if (d.isVarDeclaration() && d.needThis())
                    ve.type = d.type.addMod(e.type.mod);
                return ve;
            }
            else if (d2.isTemplateDeclaration())
            {
                return toTemplateExp(cast(TemplateDeclaration)d2);
            }
            else
                assert(0);
        }

        bool unreal = e.op == EXP.variable && (cast(VarExp)e).var.isField();
        if (d.isDataseg() || unreal && d.isField())
        {
            // (e, d)
            checkAccess(e.loc, sc, e, d);
            Expression ve = new VarExp(e.loc, d);
            e = unreal ? ve : new CommaExp(e.loc, e, ve);
            e = e.expressionSemantic(sc);
            return e;
        }

        e = new DotVarExp(e.loc, e, d);
        e = e.expressionSemantic(sc);
        return e;
    }

    switch (mt.ty)
    {
        case Tvector:    return visitVector   (mt.isTypeVector());
        case Tsarray:    return visitSArray   (mt.isTypeSArray());
        case Tstruct:    return visitStruct   (mt.isTypeStruct());
        case Tenum:      return visitEnum     (mt.isTypeEnum());
        case Terror:     return visitError    (mt.isTypeError());
        case Tarray:     return visitDArray   (mt.isTypeDArray());
        case Taarray:    return visitAArray   (mt.isTypeAArray());
        case Treference: return visitReference(mt.isTypeReference());
        case Tdelegate:  return visitDelegate (mt.isTypeDelegate());
        case Tclass:     return visitClass    (mt.isTypeClass());

        default:         return mt.isTypeBasic()
                                ? visitBasic(cast(TypeBasic)mt)
                                : visitType(mt);
    }
}

// if initializer is 0
bool isZeroInit(Type t, Loc loc)
{
    bool visitType(Type _)
    {
        return false;       // assume not
    }

    bool visitBasic(TypeBasic t)
    {
        switch (t.ty)
        {
            case Tchar:
            case Twchar:
            case Tdchar:
            case Timaginary32:
            case Timaginary64:
            case Timaginary80:
            case Tfloat32:
            case Tfloat64:
            case Tfloat80:
            case Tcomplex32:
            case Tcomplex64:
            case Tcomplex80:
                return false; // no
            default:
                return true; // yes
        }
    }

    bool visitVector(TypeVector t)
    {
        return t.basetype.isZeroInit(loc);
    }

    bool visitSArray(TypeSArray t)
    {
        return t.next.isZeroInit(loc);
    }

    bool visitStruct(TypeStruct t)
    {
        // Determine zeroInit here, as this can be called before semantic2
        t.sym.determineSize(t.sym.loc);
        return t.sym.zeroInit;
    }

    bool visitEnum(TypeEnum t)
    {
        return t.sym.getDefaultValue(loc).toBool().hasValue(false);
    }

    switch(t.ty)
    {
        default:               return t.isTypeBasic() ? visitBasic(cast(TypeBasic)t) : visitType(t);
        case Tvector:          return visitVector(t.isTypeVector());
        case Tsarray:          return visitSArray(t.isTypeSArray());
        case Taarray:
        case Tarray:
        case Treference:
        case Tdelegate:
        case Tclass:
        case Tpointer:         return true;
        case Tstruct:          return visitStruct(t.isTypeStruct());
        case Tenum:            return visitEnum(t.isTypeEnum());
    }
}


/************************
 * Get the default initialization expression for a type.
 * Params:
 *  mt = the type for which the init expression is returned
 *  loc = the location where the expression needs to be evaluated
 *  isCfile = default initializers are different with C
 *
 * Returns:
 *  The initialization expression for the type.
 */
Expression defaultInit(Type mt, Loc loc, const bool isCfile = false)
{
    Expression visitBasic(TypeBasic mt)
    {
        static if (LOGDEFAULTINIT)
        {
            printf("TypeBasic::defaultInit() '%s' isCfile: %d\n", mt.toChars(), isCfile);
        }
        dinteger_t value = 0;

        switch (mt.ty)
        {
        case Tchar:
            value = isCfile ? 0 : 0xFF;
            break;

        case Twchar:
        case Tdchar:
            value = isCfile ? 0 : 0xFFFF;
            break;

        case Timaginary32:
        case Timaginary64:
        case Timaginary80:
        case Tfloat32:
        case Tfloat64:
        case Tfloat80:
            return new RealExp(loc, isCfile ? CTFloat.zero : target.RealProperties.nan, mt);

        case Tcomplex32:
        case Tcomplex64:
        case Tcomplex80:
            {
                // Can't use fvalue + I*fvalue (the im part becomes a quiet NaN).
                const cvalue = isCfile ? complex_t(CTFloat.zero, CTFloat.zero)
                                       : complex_t(target.RealProperties.nan, target.RealProperties.nan);
                return new ComplexExp(loc, cvalue, mt);
            }

        case Tvoid:
            error(loc, "`void` does not have a default initializer");
            return ErrorExp.get();

        default:
            break;
        }
        return new IntegerExp(loc, value, mt);
    }

    Expression visitVector(TypeVector mt)
    {
        //printf("TypeVector::defaultInit()\n");
        assert(mt.basetype.ty == Tsarray);
        Expression e = mt.basetype.defaultInit(loc, isCfile);
        auto ve = new VectorExp(loc, e, mt);
        ve.type = mt;
        ve.dim = cast(int)(mt.basetype.size(loc) / mt.elementType().size(loc));
        return ve;
    }

    Expression visitSArray(TypeSArray mt)
    {
        static if (LOGDEFAULTINIT)
        {
            printf("TypeSArray::defaultInit() '%s' isCfile %d\n", mt.toChars(), isCfile);
        }
        if (mt.next.ty == Tvoid)
            return mt.tuns8.defaultInit(loc, isCfile);
        else
            return mt.next.defaultInit(loc, isCfile);
    }

    Expression visitFunction(TypeFunction mt)
    {
        error(loc, "`function` does not have a default initializer");
        return ErrorExp.get();
    }

    Expression visitStruct(TypeStruct mt)
    {
        static if (LOGDEFAULTINIT)
        {
            printf("TypeStruct::defaultInit() '%s'\n", mt.toChars());
        }
        Declaration d = new SymbolDeclaration(mt.sym.loc, mt.sym);
        assert(d);
        d.type = mt;
        d.storage_class |= STC.rvalue; // https://issues.dlang.org/show_bug.cgi?id=14398
        return new VarExp(mt.sym.loc, d);
    }

    Expression visitEnum(TypeEnum mt)
    {
        static if (LOGDEFAULTINIT)
        {
            printf("TypeEnum::defaultInit() '%s'\n", mt.toChars());
        }
        // Initialize to first member of enum
        Expression e = mt.sym.getDefaultValue(loc);
        e = e.copy();
        e.loc = loc;
        e.type = mt; // to deal with const, immutable, etc., variants
        return e;
    }

    Expression visitTuple(TypeTuple mt)
    {
        static if (LOGDEFAULTINIT)
        {
            printf("TypeTuple::defaultInit() '%s'\n", mt.toChars());
        }
        auto exps = new Expressions(mt.arguments.length);
        for (size_t i = 0; i < mt.arguments.length; i++)
        {
            Parameter p = (*mt.arguments)[i];
            assert(p.type);
            Expression e = p.type.defaultInitLiteral(loc);
            if (e.op == EXP.error)
            {
                return e;
            }
            (*exps)[i] = e;
        }
        return new TupleExp(loc, exps);
    }

    Expression visitNoreturn(TypeNoreturn mt)
    {
        static if (LOGDEFAULTINIT)
        {
            printf("TypeNoreturn::defaultInit() '%s'\n", mt.toChars());
        }
        auto cond = IntegerExp.createBool(false);
        auto msg = new StringExp(loc, "Accessed expression of type `noreturn`");
        msg.type = Type.tstring;
        auto ae = new AssertExp(loc, cond, msg);
        ae.type = mt;
        return ae;
    }

    switch (mt.ty)
    {
        case Tvector:   return visitVector  (mt.isTypeVector());
        case Tsarray:   return visitSArray  (mt.isTypeSArray());
        case Tfunction: return visitFunction(mt.isTypeFunction());
        case Tstruct:   return visitStruct  (mt.isTypeStruct());
        case Tenum:     return visitEnum    (mt.isTypeEnum());
        case Ttuple:    return visitTuple   (mt.isTypeTuple());

        case Tnull:     return new NullExp(Loc.initial, Type.tnull);

        case Terror:    return ErrorExp.get();

        case Tarray:
        case Taarray:
        case Tpointer:
        case Treference:
        case Tdelegate:
        case Tclass:    return new NullExp(loc, mt);
        case Tnoreturn: return visitNoreturn(mt.isTypeNoreturn());

        default:        return mt.isTypeBasic() ?
                                visitBasic(cast(TypeBasic)mt) :
                                null;
    }
}

/*
If `type` resolves to a dsymbol, then that
dsymbol is returned.

Params:
  type = the type that is checked
  sc   = the scope where the type is used

Returns:
  The dsymbol to which the type resolve or `null`
  if the type does resolve to any symbol (for example,
  in the case of basic types).
*/
Dsymbol toDsymbol(Type type, Scope* sc)
{
    Dsymbol visitType(Type _)            { return null; }
    Dsymbol visitStruct(TypeStruct type) { return type.sym; }
    Dsymbol visitEnum(TypeEnum type)     { return type.sym; }
    Dsymbol visitClass(TypeClass type)   { return type.sym; }

    Dsymbol visitTraits(TypeTraits type)
    {
        Type t;
        Expression e;
        Dsymbol s;
        resolve(type, type.loc, sc, e, t, s);
        if (t && t.ty != Terror)
            s = t.toDsymbol(sc);
        else if (e)
            s = getDsymbol(e);

        return s;
    }

    Dsymbol visitMixin(TypeMixin type)
    {
        Type t;
        Expression e;
        Dsymbol s;
        resolve(type, type.loc, sc, e, t, s);
        if (t)
            s = t.toDsymbol(sc);
        else if (e)
            s = getDsymbol(e);

        return s;
    }

    Dsymbol visitIdentifier(TypeIdentifier type)
    {
        //printf("TypeIdentifier::toDsymbol('%s')\n", toChars(type));
        if (!sc)
            return null;

        Type t;
        Expression e;
        Dsymbol s;
        resolve(type, type.loc, sc, e, t, s);
        if (t && t.ty != Tident)
            s = t.toDsymbol(sc);
        if (e)
            s = getDsymbol(e);
        return s;
    }

    Dsymbol visitInstance(TypeInstance type)
    {
        Type t;
        Expression e;
        Dsymbol s;
        //printf("TypeInstance::semantic(%s)\n", toChars());
        resolve(type, type.loc, sc, e, t, s);
        if (t && t.ty != Tinstance)
            s = t.toDsymbol(sc);
        return s;
    }

    Dsymbol visitTypeof(TypeTypeof type)
    {
        //printf("TypeTypeof::toDsymbol('%s')\n", toChars());
        Expression e;
        Type t;
        Dsymbol s;
        resolve(type, type.loc, sc, e, t, s);
        return s;
    }

    Dsymbol visitReturn(TypeReturn type)
    {
        Expression e;
        Type t;
        Dsymbol s;
        resolve(type, type.loc, sc, e, t, s);
        return s;
    }

    switch(type.ty)
    {
        default:                return visitType(type);
        case Ttraits:           return visitTraits(type.isTypeTraits());
        case Tmixin:            return visitMixin(type.isTypeMixin());
        case Tident:            return visitIdentifier(type.isTypeIdentifier());
        case Tinstance:         return visitInstance(type.isTypeInstance());
        case Ttypeof:           return visitTypeof(type.isTypeTypeof());
        case Treturn:           return visitReturn(type.isTypeReturn());
        case Tstruct:           return visitStruct(type.isTypeStruct());
        case Tenum:             return visitEnum(type.isTypeEnum());
        case Tclass:            return visitClass(type.isTypeClass());
    }
}

/************************************
 * Add storage class modifiers to type.
 */
Type addStorageClass(Type type, STC stc)
{
    Type visitType(Type t)
    {
        /* Just translate to MOD bits and let addMod() do the work
         */
        MOD mod = 0;
        if (stc & STC.immutable_)
            mod = MODFlags.immutable_;
        else
        {
            if (stc & (STC.const_ | STC.in_))
                mod |= MODFlags.const_;
            if (stc & STC.wild)
                mod |= MODFlags.wild;
            if (stc & STC.shared_)
                mod |= MODFlags.shared_;
        }
        return t.addMod(mod);
    }

    Type visitFunction(TypeFunction tf_src)
    {
        //printf("addStorageClass(%llx) %d\n", stc, (stc & STC.scope_) != 0);
        TypeFunction t = visitType(tf_src).toTypeFunction();
        if ((stc & STC.pure_ && !t.purity) ||
            (stc & STC.nothrow_ && !t.isNothrow) ||
            (stc & STC.nogc && !t.isNogc) ||
            (stc & STC.scope_ && !t.isScopeQual) ||
            (stc & STC.safe && t.trust < TRUST.trusted))
        {
            // Klunky to change these
            auto tf = new TypeFunction(t.parameterList, t.next, t.linkage, STC.none);
            tf.mod = t.mod;
            tf.inferenceArguments = tf_src.inferenceArguments;
            tf.purity = t.purity;
            tf.isNothrow = t.isNothrow;
            tf.isNogc = t.isNogc;
            tf.isProperty = t.isProperty;
            tf.isRef = t.isRef;
            tf.isReturn = t.isReturn;
            tf.isReturnScope = t.isReturnScope;
            tf.isScopeQual = t.isScopeQual;
            tf.isReturnInferred = t.isReturnInferred;
            tf.isScopeInferred = t.isScopeInferred;
            tf.trust = t.trust;
            tf.isInOutParam = t.isInOutParam;
            tf.isInOutQual = t.isInOutQual;
            tf.isCtor = t.isCtor;

            if (stc & STC.pure_)
                tf.purity = PURE.fwdref;
            if (stc & STC.nothrow_)
                tf.isNothrow = true;
            if (stc & STC.nogc)
                tf.isNogc = true;
            if (stc & STC.safe)
                tf.trust = TRUST.safe;
            if (stc & STC.scope_)
            {
                tf.isScopeQual = true;
                if (stc & STC.scopeinferred)
                    tf.isScopeInferred = true;
            }

            tf.deco = tf.merge().deco;
            t = tf;
        }
        return t;
    }

    Type visitDelegate(TypeDelegate tdg)
    {
        TypeDelegate t = visitType(tdg).isTypeDelegate();
        return t;
    }

    switch(type.ty)
    {
        default:            return visitType(type);
        case Tfunction:     return visitFunction(type.isTypeFunction());
        case Tdelegate:     return visitDelegate(type.isTypeDelegate());
    }
}

/**********************************************
 * Extract complex type from core.stdc.config
 * Params:
 *      loc = for error messages
 *      sc = context
 *      ty = a complex or imaginary type
 * Returns:
 *      Complex!float, Complex!double, Complex!real or null for error
 */

Type getComplexLibraryType(Loc loc, Scope* sc, TY ty)
{
    // singleton
    __gshared Type complex_float;
    __gshared Type complex_double;
    __gshared Type complex_real;

    Type* pt;
    Identifier id;
    switch (ty)
    {
        case Timaginary32:
        case Tcomplex32:   id = Id.c_complex_float;  pt = &complex_float;  break;
        case Timaginary64:
        case Tcomplex64:   id = Id.c_complex_double; pt = &complex_double; break;
        case Timaginary80:
        case Tcomplex80:   id = Id.c_complex_real;   pt = &complex_real;   break;
        default:
             return Type.terror;
    }

    if (*pt)
        return *pt;
    *pt = Type.terror;

    Module mConfig = Module.loadCoreStdcConfig();
    if (!mConfig)
    {
        error(loc, "`core.stdc.config` is required for complex numbers");
        return *pt;
    }

    Dsymbol s = mConfig.searchX(Loc.initial, sc, id, SearchOpt.ignorePrivateImports);
    if (!s)
    {
        error(loc, "`%s` not found in core.stdc.config", id.toChars());
        return *pt;
    }
    s = s.toAlias();
    if (auto t = s.getType())
    {
        if (auto ts = t.toBasetype().isTypeStruct())
        {
            *pt = ts;
            return ts;
        }
    }
    if (auto sd = s.isStructDeclaration())
    {
        *pt = sd.type;
        return sd.type;
    }

    error(loc, "`%s` must be an alias for a complex struct", s.toChars());
    return *pt;
}

/*******************************
 * Covariant means that 'src' can substitute for 't',
 * i.e. a pure function is a match for an impure type.
 * Params:
 *      src = source type
 *      t = type 'src' is covariant with
 *      pstc = if not null, store STCxxxx which would make it covariant
 *      cppCovariant = true if extern(C++) function types should follow C++ covariant rules
 * Returns:
 *     An enum value of either `Covariant.yes` or a reason it's not covariant.
 */
Covariant covariant(Type src, Type t, STC* pstc = null, bool cppCovariant = false)
{
    version (none)
    {
        printf("Type::covariant(t = %s) %s\n", t.toChars(), src.toChars());
        printf("deco = %p, %p\n", src.deco, t.deco);
        //    printf("ty = %d\n", next.ty);
        printf("mod = %x, %x\n", src.mod, t.mod);
    }
    if (pstc)
        *pstc = STC.none;
    STC stc = STC.none;

    bool notcovariant = false;

    if (src.equals(t))
        return Covariant.yes;

    TypeFunction t1 = src.isTypeFunction();
    TypeFunction t2 = t.isTypeFunction();

    if (!t1 || !t2)
        goto Ldistinct;

    if (t1.parameterList.varargs != t2.parameterList.varargs)
        goto Ldistinct;

    if (t1.parameterList.parameters && t2.parameterList.parameters)
    {
        if (t1.parameterList.length != t2.parameterList.length)
            goto Ldistinct;

        foreach (i, fparam1; t1.parameterList)
        {
            Parameter fparam2 = t2.parameterList[i];
            Type tp1 = fparam1.type;
            Type tp2 = fparam2.type;

            if (!tp1.equals(tp2))
            {
                if (tp1.ty == tp2.ty)
                {
                    if (auto tc1 = tp1.isTypeClass())
                    {
                        if (tc1.sym == (cast(TypeClass)tp2).sym && MODimplicitConv(tp2.mod, tp1.mod))
                            goto Lcov;
                    }
                    else if (auto ts1 = tp1.isTypeStruct())
                    {
                        if (ts1.sym == (cast(TypeStruct)tp2).sym && MODimplicitConv(tp2.mod, tp1.mod))
                            goto Lcov;
                    }
                    else if (tp1.ty == Tpointer)
                    {
                        if (tp2.implicitConvTo(tp1))
                            goto Lcov;
                    }
                    else if (tp1.ty == Tarray)
                    {
                        if (tp2.implicitConvTo(tp1))
                            goto Lcov;
                    }
                    else if (tp1.ty == Tdelegate)
                    {
                        if (tp2.implicitConvTo(tp1))
                            goto Lcov;
                    }
                }
                goto Ldistinct;
            }
        Lcov:
            notcovariant |= !fparam1.isCovariant(t1.isRef, fparam2);

            /* https://issues.dlang.org/show_bug.cgi?id=23135
             * extern(C++) mutable parameters are not covariant with const.
             */
            if (t1.linkage == LINK.cpp && cppCovariant)
            {
                notcovariant |= tp1.isNaked() != tp2.isNaked();
                if (auto tpn1 = tp1.nextOf())
                    notcovariant |= tpn1.isNaked() != tp2.nextOf().isNaked();
            }
        }
    }
    else if (t1.parameterList.parameters != t2.parameterList.parameters)
    {
        if (t1.parameterList.length || t2.parameterList.length)
            goto Ldistinct;
    }

    // The argument lists match
    if (notcovariant)
        goto Lnotcovariant;
    if (t1.linkage != t2.linkage)
        goto Lnotcovariant;

    {
        // Return types
        Type t1n = t1.next;
        Type t2n = t2.next;

        if (!t1n || !t2n) // happens with return type inference
            goto Lnotcovariant;

        if (t1n.equals(t2n))
            goto Lcovariant;
        if (t1n.ty == Tclass && t2n.ty == Tclass)
        {
            /* If same class type, but t2n is const, then it's
             * covariant. Do this test first because it can work on
             * forward references.
             */
            if ((cast(TypeClass)t1n).sym == (cast(TypeClass)t2n).sym && MODimplicitConv(t1n.mod, t2n.mod))
                goto Lcovariant;

            // If t1n is forward referenced:
            ClassDeclaration cd = (cast(TypeClass)t1n).sym;
            if (cd.semanticRun < PASS.semanticdone && !cd.isBaseInfoComplete())
                cd.dsymbolSemantic(null);
            if (!cd.isBaseInfoComplete())
            {
                return Covariant.fwdref;
            }
        }
        if (t1n.ty == Tstruct && t2n.ty == Tstruct)
        {
            if ((cast(TypeStruct)t1n).sym == (cast(TypeStruct)t2n).sym && MODimplicitConv(t1n.mod, t2n.mod))
                goto Lcovariant;
        }
        else if (t1n.ty == t2n.ty && t1n.implicitConvTo(t2n))
        {
            if (t1.isRef && t2.isRef)
            {
                // Treat like pointers to t1n and t2n
                if (t1n.constConv(t2n) < MATCH.constant)
                    goto Lnotcovariant;
            }
            goto Lcovariant;
        }
        else if (t1n.ty == Tnull)
        {
            // NULL is covariant with any pointer type, but not with any
            // dynamic arrays, associative arrays or delegates.
            // https://issues.dlang.org/show_bug.cgi?id=8589
            // https://issues.dlang.org/show_bug.cgi?id=19618
            Type t2bn = t2n.toBasetype();
            if (t2bn.ty == Tnull || t2bn.ty == Tpointer || t2bn.ty == Tclass)
                goto Lcovariant;
        }
        // bottom type is covariant to any type
        else if (t1n.ty == Tnoreturn)
            goto Lcovariant;
    }
    goto Lnotcovariant;

Lcovariant:
    if (t1.isRef != t2.isRef)
        goto Lnotcovariant;

    if (!t1.isRef && (t1.isScopeQual || t2.isScopeQual))
    {
        STC stc1 = t1.isScopeQual ? STC.scope_ : STC.none;
        STC stc2 = t2.isScopeQual ? STC.scope_ : STC.none;
        if (t1.isReturn)
        {
            stc1 |= STC.return_;
            if (!t1.isScopeQual)
                stc1 |= STC.ref_;
        }
        if (t2.isReturn)
        {
            stc2 |= STC.return_;
            if (!t2.isScopeQual)
                stc2 |= STC.ref_;
        }
        if (!Parameter.isCovariantScope(t1.isRef, stc1, stc2))
            goto Lnotcovariant;
    }

    // We can subtract 'return ref' from 'this', but cannot add it
    else if (t1.isReturn && !t2.isReturn)
        goto Lnotcovariant;

    /* https://issues.dlang.org/show_bug.cgi?id=23135
     * extern(C++) mutable member functions are not covariant with const.
     */
    if (t1.linkage == LINK.cpp && cppCovariant && t1.isNaked() != t2.isNaked())
        goto Lnotcovariant;

    /* Can convert mutable to const
     */
    if (!MODimplicitConv(t2.mod, t1.mod))
    {
        version (none)
        {
            //stop attribute inference with const
            // If adding 'const' will make it covariant
            if (MODimplicitConv(t2.mod, MODmerge(t1.mod, MODFlags.const_)))
                stc |= STC.const_;
            else
                goto Lnotcovariant;
        }
        else
        {
            goto Ldistinct;
        }
    }

    /* Can convert pure to impure, nothrow to throw, and nogc to gc
     */
    if (!t1.purity && t2.purity)
        stc |= STC.pure_;

    if (!t1.isNothrow && t2.isNothrow)
        stc |= STC.nothrow_;

    if (!t1.isNogc && t2.isNogc)
        stc |= STC.nogc;

    /* Can convert safe/trusted to system
     */
    if (t1.trust <= TRUST.system && t2.trust >= TRUST.trusted)
    {
        // Should we infer trusted or safe? Go with safe.
        stc |= STC.safe;
    }

    if (stc)
    {
        if (pstc)
            *pstc = stc;
        goto Lnotcovariant;
    }

    //printf("\tcovaraint: 1\n");
    return Covariant.yes;

Ldistinct:
    //printf("\tcovaraint: 0\n");
    return Covariant.distinct;

Lnotcovariant:
    //printf("\tcovaraint: 2\n");
    return Covariant.no;
}

/************************************
 * Take the specified storage class for p,
 * and use the function signature to infer whether
 * STC.scope_ and STC.return_ should be OR'd in.
 * (This will not affect the name mangling.)
 * Params:
 *  tf = TypeFunction to use to get the signature from
 *  tthis = type of `this` parameter, null if none
 *  p = parameter to this function
 *  outerVars = context variables p could escape into, if any
 *  indirect = is this for an indirect or virtual function call?
 * Returns:
 *  storage class with STC.scope_ or STC.return_ OR'd in
 */
STC parameterStorageClass(TypeFunction tf, Type tthis, Parameter p, VarDeclarations* outerVars = null,
    bool indirect = false)
{
    //printf("parameterStorageClass(p: %s)\n", p.toChars());
    auto stc = p.storageClass;

    // When the preview switch is enable, `in` parameters are `scope`
    if (stc & STC.constscoperef)
        return stc | STC.scope_;

    if (stc & (STC.scope_ | STC.return_ | STC.lazy_) || tf.purity == PURE.impure)
        return stc;

    /* If haven't inferred the return type yet, can't infer storage classes
     */
    if (!tf.nextOf() || !tf.isNothrow())
        return stc;

    tf.purityLevel();

    static bool mayHavePointers(Type t)
    {
        if (auto ts = t.isTypeStruct())
        {
            auto sym = ts.sym;
            if (sym.members && !sym.determineFields() && sym.type != Type.terror)
                // struct is forward referenced, so "may have" pointers
                return true;
        }
        return t.hasPointers();
    }

    // See if p can escape via any of the other parameters
    if (tf.purity == PURE.weak)
    {
        /*
         * Indirect calls may escape p through a nested context
         * See:
         *   https://issues.dlang.org/show_bug.cgi?id=24212
         *   https://issues.dlang.org/show_bug.cgi?id=24213
         */
        if (indirect)
            return stc;

        // Check escaping through parameters
        foreach (i, fparam; tf.parameterList)
        {
            Type t = fparam.type;
            if (!t)
                continue;
            t = t.baseElemOf();     // punch thru static arrays
            if (t.isMutable() && t.hasPointers())
            {
                if (fparam.isReference() && fparam != p)
                    return stc;

                if (t.ty == Tdelegate)
                    return stc;     // could escape thru delegate

                if (t.ty == Tclass)
                    return stc;

                /* if t is a pointer to mutable pointer
                 */
                if (auto tn = t.nextOf())
                {
                    if (tn.isMutable() && mayHavePointers(tn))
                        return stc;   // escape through pointers
                }
            }
        }

        // Check escaping through `this`
        if (tthis && tthis.isMutable())
        {
            foreach (VarDeclaration v; isAggregate(tthis).fields)
            {
                if (v.hasPointers())
                    return stc;
            }
        }

        // Check escaping through nested context
        if (outerVars && tf.isMutable())
        {
            foreach (VarDeclaration v; *outerVars)
            {
                if (v.hasPointers())
                    return stc;
            }
        }
    }

    // Check escaping through return value
    Type tret = tf.nextOf().toBasetype();
    if (tf.isRef || tret.hasPointers())
    {
        return stc | STC.scope_ | STC.return_ | STC.returnScope;
    }
    else
        return stc | STC.scope_;
}

bool isBaseOf(Type tthis, Type t, int* poffset)
{
    auto tc = tthis.isTypeClass();
    if (!tc)
        return false;

    if (!t || t.ty != Tclass)
        return false;

    ClassDeclaration cd = t.isTypeClass().sym;
    if (cd.semanticRun < PASS.semanticdone && !cd.isBaseInfoComplete())
        cd.dsymbolSemantic(null);
    if (tc.sym.semanticRun < PASS.semanticdone && !tc.sym.isBaseInfoComplete())
        tc.sym.dsymbolSemantic(null);

    if (tc.sym.isBaseOf(cd, poffset))
        return true;

    return false;
}

bool equivalent(Type src, Type t)
{
    return immutableOf(src).equals(t.immutableOf());
}

Type pointerTo(Type type)
{
    if (type.ty == Terror)
        return type;
    auto mcache = type.getMcache();
    if (!mcache.pto)
    {
        Type t = new TypePointer(type);
        if (type.ty == Tfunction)
        {
            t.deco = t.merge().deco;
            mcache.pto = t;
        }
        else
            mcache.pto = t.merge();
    }
    return mcache.pto;
}

Type referenceTo(Type type)
{
    if (type.ty == Terror)
        return type;
    auto mcache = type.getMcache();
    if (!mcache.rto)
    {
        Type t = new TypeReference(type);
        mcache.rto = t.merge();
    }
    return mcache.rto;
}

// Make corresponding static array type without semantic
Type sarrayOf(Type type, dinteger_t dim)
{
    assert(type.deco);
    Type t = new TypeSArray(type, new IntegerExp(Loc.initial, dim, Type.tsize_t));
    // according to TypeSArray.semantic()
    t = t.addMod(type.mod);
    t = t.merge();
    return t;
}

Type arrayOf(Type type)
{
    if (type.ty == Terror)
        return type;
    auto mcache = type.getMcache();
    if (!mcache.arrayof)
    {
        Type t = new TypeDArray(type);
        mcache.arrayof = t.merge();
    }
    return mcache.arrayof;
}

/********************************
 * Convert to 'const'.
 */
Type constOf(Type type)
{
    //printf("Type::constOf() %p %s\n", type, type.toChars());
    if (type.mod == MODFlags.const_)
        return type;
    if (type.mcache && type.mcache.cto)
    {
        assert(type.mcache.cto.mod == MODFlags.const_);
        return type.mcache.cto;
    }
    Type t = type.makeConst();
    t = t.merge();
    t.fixTo(type);
    //printf("-Type::constOf() %p %s\n", t, t.toChars());
    return t;
}

/********************************
 * Convert to 'immutable'.
 */
Type immutableOf(Type type)
{
    //printf("Type::immutableOf() %p %s\n", this, toChars());
    if (type.isImmutable())
        return type;
    if (type.mcache && type.mcache.ito)
    {
        assert(type.mcache.ito.isImmutable());
        return type.mcache.ito;
    }
    Type t = type.makeImmutable();
    t = t.merge();
    t.fixTo(type);
    //printf("\t%p\n", t);
    return t;
}

/********************************
 * Make type mutable.
 */
Type mutableOf(Type type)
{
    //printf("Type::mutableOf() %p, %s\n", type, type.toChars());
    Type t = type;
    if (type.isImmutable())
    {
        type.getMcache();
        t = type.mcache.ito; // immutable => naked
        assert(!t || (t.isMutable() && !t.isShared()));
    }
    else if (type.isConst())
    {
        type.getMcache();
        if (type.isShared())
        {
            if (type.isWild())
                t = type.mcache.swcto; // shared wild const -> shared
            else
                t = type.mcache.sto; // shared const => shared
        }
        else
        {
            if (type.isWild())
                t = type.mcache.wcto; // wild const -> naked
            else
                t = type.mcache.cto; // const => naked
        }
        assert(!t || t.isMutable());
    }
    else if (type.isWild())
    {
        type.getMcache();
        if (type.isShared())
            t = type.mcache.sto; // shared wild => shared
        else
            t = type.mcache.wto; // wild => naked
        assert(!t || t.isMutable());
    }
    if (!t)
    {
        t = type.makeMutable();
        t = t.merge();
        t.fixTo(type);
    }
    else
        t = t.merge();
    assert(t.isMutable());
    return t;
}

Type sharedOf(Type type)
{
    //printf("Type::sharedOf() %p, %s\n", type, type.toChars());
    if (type.mod == MODFlags.shared_)
        return type;
    if (type.mcache && type.mcache.sto)
    {
        assert(type.mcache.sto.mod == MODFlags.shared_);
        return type.mcache.sto;
    }
    Type t = type.makeShared();
    t = t.merge();
    t.fixTo(type);
    //printf("\t%p\n", t);
    return t;
}

Type sharedConstOf(Type type)
{
    //printf("Type::sharedConstOf() %p, %s\n", type, type.toChars());
    if (type.mod == (MODFlags.shared_ | MODFlags.const_))
        return type;
    if (type.mcache && type.mcache.scto)
    {
        assert(type.mcache.scto.mod == (MODFlags.shared_ | MODFlags.const_));
        return type.mcache.scto;
    }
    Type t = type.makeSharedConst();
    t = t.merge();
    t.fixTo(type);
    //printf("\t%p\n", t);
    return t;
}

/********************************
 * Make type unshared.
 *      0            => 0
 *      const        => const
 *      immutable    => immutable
 *      shared       => 0
 *      shared const => const
 *      wild         => wild
 *      wild const   => wild const
 *      shared wild  => wild
 *      shared wild const => wild const
 */
Type unSharedOf(Type type)
{
    //printf("Type::unSharedOf() %p, %s\n", type, type.toChars());
    Type t = type;

    if (type.isShared())
    {
        type.getMcache();
        if (type.isWild())
        {
            if (type.isConst())
                t = type.mcache.wcto; // shared wild const => wild const
            else
                t = type.mcache.wto; // shared wild => wild
        }
        else
        {
            if (type.isConst())
                t = type.mcache.cto; // shared const => const
            else
                t = type.mcache.sto; // shared => naked
        }
        assert(!t || !t.isShared());
    }

    if (!t)
    {
        t = type.nullAttributes();
        t.mod = type.mod & ~MODFlags.shared_;
        t.ctype = type.ctype;
        t = t.merge();
        t.fixTo(type);
    }
    else
        t = t.merge();
    assert(!t.isShared());
    return t;
}

/********************************
 * Convert to 'wild'.
 */
Type wildOf(Type type)
{
    //printf("Type::wildOf() %p %s\n", type, type.toChars());
    if (type.mod == MODFlags.wild)
        return type;
    if (type.mcache && type.mcache.wto)
    {
        assert(type.mcache.wto.mod == MODFlags.wild);
        return type.mcache.wto;
    }
    Type t = type.makeWild();
    t = t.merge();
    t.fixTo(type);
    //printf("\t%p %s\n", t, t.toChars());
    return t;
}

Type wildConstOf(Type type)
{
    //printf("Type::wildConstOf() %p %s\n", type, type.toChars());
    if (type.mod == MODFlags.wildconst)
        return type;
    if (type.mcache && type.mcache.wcto)
    {
        assert(type.mcache.wcto.mod == MODFlags.wildconst);
        return type.mcache.wcto;
    }
    Type t = type.makeWildConst();
    t = t.merge();
    t.fixTo(type);
    //printf("\t%p %s\n", t, t.toChars());
    return t;
}

Type sharedWildOf(Type type)
{
    //printf("Type::sharedWildOf() %p, %s\n", type, type.toChars());
    if (type.mod == (MODFlags.shared_ | MODFlags.wild))
        return type;
    if (type.mcache && type.mcache.swto)
    {
        assert(type.mcache.swto.mod == (MODFlags.shared_ | MODFlags.wild));
        return type.mcache.swto;
    }
    Type t = type.makeSharedWild();
    t = t.merge();
    t.fixTo(type);
    //printf("\t%p %s\n", t, t.toChars());
    return t;
}

Type sharedWildConstOf(Type type)
{
    //printf("Type::sharedWildConstOf() %p, %s\n", type, type.toChars());
    if (type.mod == (MODFlags.shared_ | MODFlags.wildconst))
        return type;
    if (type.mcache && type.mcache.swcto)
    {
        assert(type.mcache.swcto.mod == (MODFlags.shared_ | MODFlags.wildconst));
        return type.mcache.swcto;
    }
    Type t = type.makeSharedWildConst();
    t = t.merge();
    t.fixTo(type);
    //printf("\t%p %s\n", t, t.toChars());
    return t;
}

Type nakedOf(Type type)
{
    //printf("Type::nakedOf() %p, %s\n", type, type.toChars());
    if (type.mod == 0)
        return type;
    if (type.mcache) with(type.mcache)
    {
        // the cache has the naked type at the "identity" position, try to find it
        if (cto && cto.mod == 0)
            return cto;
        if (ito && ito.mod == 0)
            return ito;
        if (sto && sto.mod == 0)
            return sto;
        if (scto && scto.mod == 0)
            return scto;
        if (wto && wto.mod == 0)
            return wto;
        if (wcto && wcto.mod == 0)
            return wcto;
        if (swto && swto.mod == 0)
            return swto;
        if (swcto && swcto.mod == 0)
            return swcto;
    }
    Type t = type.nullAttributes();
    t.mod = 0;
    t = t.merge();
    t.fixTo(type);
    //printf("\t%p %s\n", t, t.toChars());
    return t;
}

Type unqualify(Type type, uint m)
{
    Type t = type.mutableOf().unSharedOf();

    Type tn = type.ty == Tenum ? null : type.nextOf();
    if (tn && tn.ty != Tfunction)
    {
        Type utn = tn.unqualify(m);
        if (utn != tn)
        {
            if (type.ty == Tpointer)
                t = utn.pointerTo();
            else if (type.ty == Tarray)
                t = utn.arrayOf();
            else if (type.ty == Tsarray)
                t = new TypeSArray(utn, (cast(TypeSArray)type).dim);
            else if (type.ty == Taarray)
            {
                t = new TypeAArray(utn, (cast(TypeAArray)type).index);
            }
            else
                assert(0);

            t = t.merge();
        }
    }
    t = t.addMod(type.mod & ~m);
    return t;
}

/**************************
 * Return type with the top level of it being mutable.
 *
 * Params:
 *  t = type for which the top level mutable version is being returned
 *
 * Returns:
 *  type version with mutable top level
 */
Type toHeadMutable(const Type t)
{
    Type unqualType = cast(Type) t;
    if (t.isTypeStruct() || t.isTypeClass())
        return unqualType;

    if (!t.mod)
        return unqualType;
    return unqualType.mutableOf();
}

Type aliasthisOf(Type type)
{
    auto ad = isAggregate(type);
    if (!ad || !ad.aliasthis)
        return null;

    auto s = ad.aliasthis.sym;
    if (s.isAliasDeclaration())
        s = s.toAlias();

    if (s.isTupleDeclaration())
        return null;

    if (auto vd = s.isVarDeclaration())
    {
        auto t = vd.type;
        if (vd.needThis())
            t = t.addMod(type.mod);
        return t;
    }
    Dsymbol callable = s.isFuncDeclaration();
    callable = callable ? callable : s.isTemplateDeclaration();
    if (callable)
    {
        auto fd = resolveFuncCall(Loc.initial, null, callable, null, type, ArgumentList(), FuncResolveFlag.quiet);
        if (!fd || fd.errors || !functionSemantic(fd))
            return Type.terror;

        auto t = fd.type.nextOf();
        if (!t) // https://issues.dlang.org/show_bug.cgi?id=14185
            return Type.terror;
        t = t.substWildTo(type.mod == 0 ? MODFlags.mutable : type.mod);
        return t;
    }
    if (auto d = s.isDeclaration())
    {
        assert(d.type);
        return d.type;
    }
    if (auto ed = s.isEnumDeclaration())
    {
        return ed.type;
    }

    //printf("%s\n", s.kind());
    return null;
}

/************************************
 * Apply MODxxxx bits to existing type.
 */
Type castMod(Type type, MOD mod)
{
    Type t;
    switch (mod)
    {
    case 0:
        t = type.unSharedOf().mutableOf();
        break;

    case MODFlags.const_:
        t = type.unSharedOf().constOf();
        break;

    case MODFlags.wild:
        t = type.unSharedOf().wildOf();
        break;

    case MODFlags.wildconst:
        t = type.unSharedOf().wildConstOf();
        break;

    case MODFlags.shared_:
        t = type.mutableOf().sharedOf();
        break;

    case MODFlags.shared_ | MODFlags.const_:
        t = type.sharedConstOf();
        break;

    case MODFlags.shared_ | MODFlags.wild:
        t = type.sharedWildOf();
        break;

    case MODFlags.shared_ | MODFlags.wildconst:
        t = type.sharedWildConstOf();
        break;

    case MODFlags.immutable_:
        t = type.immutableOf();
        break;

    default:
        assert(0);
    }
    return t;
}

Type substWildTo(Type type, uint mod)
{
    auto tf = type.isTypeFunction();
    if (!tf)
    {
        //printf("+Type.substWildTo this = %s, mod = x%x\n", toChars(), mod);
        Type t;

        if (Type tn = type.nextOf())
        {
            // substitution has no effect on function pointer type.
            if (type.ty == Tpointer && tn.ty == Tfunction)
            {
                t = type;
                goto L1;
            }

            t = tn.substWildTo(mod);
            if (t == tn)
                t = type;
            else
            {
                if (type.ty == Tpointer)
                    t = t.pointerTo();
                else if (type.ty == Tarray)
                    t = t.arrayOf();
                else if (type.ty == Tsarray)
                    t = new TypeSArray(t, (cast(TypeSArray)type).dim.syntaxCopy());
                else if (type.ty == Taarray)
                {
                    t = new TypeAArray(t, (cast(TypeAArray)type).index.substWildTo(mod));
                }
                else if (type.ty == Tdelegate)
                {
                    t = new TypeDelegate(t.isTypeFunction());
                }
                else
                    assert(0);

                t = t.merge();
            }
        }
        else
            t = type;

    L1:
        if (type.isWild())
        {
            if (mod == MODFlags.immutable_)
            {
                t = t.immutableOf();
            }
            else if (mod == MODFlags.wildconst)
            {
                t = t.wildConstOf();
            }
            else if (mod == MODFlags.wild)
            {
                if (type.isWildConst())
                    t = t.wildConstOf();
                else
                    t = t.wildOf();
            }
            else if (mod == MODFlags.const_)
            {
                t = t.constOf();
            }
            else
            {
                if (type.isWildConst())
                    t = t.constOf();
                else
                    t = t.mutableOf();
            }
        }
        if (type.isConst())
            t = t.addMod(MODFlags.const_);
        if (type.isShared())
            t = t.addMod(MODFlags.shared_);

        //printf("-Type.substWildTo t = %s\n", t.toChars());
        return t;
    }

    if (!tf.iswild && !(tf.mod & MODFlags.wild))
        return tf;

    // Substitude inout qualifier of function type to mutable or immutable
    // would break type system. Instead substitude inout to the most weak
    // qualifer - const.
    uint m = MODFlags.const_;

    assert(tf.next);
    Type tret = tf.next.substWildTo(m);
    Parameters* params = tf.parameterList.parameters;
    if (tf.mod & MODFlags.wild)
        params = tf.parameterList.parameters.copy();
    for (size_t i = 0; i < params.length; i++)
    {
        Parameter p = (*params)[i];
        Type t = p.type.substWildTo(m);
        if (t == p.type)
            continue;
        if (params == tf.parameterList.parameters)
            params = tf.parameterList.parameters.copy();
        (*params)[i] = new Parameter(p.loc, p.storageClass, t, null, null, null);
    }
    if (tf.next == tret && params == tf.parameterList.parameters)
        return tf;

    // Similar to TypeFunction.syntaxCopy;
    auto t = new TypeFunction(ParameterList(params, tf.parameterList.varargs), tret, tf.linkage);
    t.mod = ((tf.mod & MODFlags.wild) ? (tf.mod & ~MODFlags.wild) | MODFlags.const_ : tf.mod);
    t.isNothrow = tf.isNothrow;
    t.isNogc = tf.isNogc;
    t.purity = tf.purity;
    t.isProperty = tf.isProperty;
    t.isRef = tf.isRef;
    t.isReturn = tf.isReturn;
    t.isReturnScope = tf.isReturnScope;
    t.isScopeQual = tf.isScopeQual;
    t.isReturnInferred = tf.isReturnInferred;
    t.isScopeInferred = tf.isScopeInferred;
    t.isInOutParam = false;
    t.isInOutQual = false;
    t.trust = tf.trust;
    t.inferenceArguments = tf.inferenceArguments;
    t.isCtor = tf.isCtor;
    return t.merge();
}

/************************************
 * Add MODxxxx bits to existing type.
 * We're adding, not replacing, so adding const to
 * a shared type => "shared const"
 */
Type addMod(Type type, MOD mod)
{
    /* Add anything to immutable, and it remains immutable
     */
    Type t = type;
    if (!t.isImmutable())
    {
        //printf("addMod(%x) %s\n", mod, toChars());
        switch (mod)
        {
        case 0:
            break;

        case MODFlags.const_:
            if (type.isShared())
            {
                if (type.isWild())
                    t = type.sharedWildConstOf();
                else
                    t = type.sharedConstOf();
            }
            else
            {
                if (type.isWild())
                    t = type.wildConstOf();
                else
                    t = t.constOf();
            }
            break;

        case MODFlags.wild:
            if (type.isShared())
            {
                if (type.isConst())
                    t = type.sharedWildConstOf();
                else
                    t = type.sharedWildOf();
            }
            else
            {
                if (type.isConst())
                    t = type.wildConstOf();
                else
                    t = type.wildOf();
            }
            break;

        case MODFlags.wildconst:
            if (type.isShared())
                t = type.sharedWildConstOf();
            else
                t = type.wildConstOf();
            break;

        case MODFlags.shared_:
            if (type.isWild())
            {
                if (type.isConst())
                    t = type.sharedWildConstOf();
                else
                    t = type.sharedWildOf();
            }
            else
            {
                if (type.isConst())
                    t = type.sharedConstOf();
                else
                    t = type.sharedOf();
            }
            break;

        case MODFlags.shared_ | MODFlags.const_:
            if (type.isWild())
                t = type.sharedWildConstOf();
            else
                t = type.sharedConstOf();
            break;

        case MODFlags.shared_ | MODFlags.wild:
            if (type.isConst())
                t = type.sharedWildConstOf();
            else
                t = type.sharedWildOf();
            break;

        case MODFlags.shared_ | MODFlags.wildconst:
            t = type.sharedWildConstOf();
            break;

        case MODFlags.immutable_:
            t = type.immutableOf();
            break;

        default:
            assert(0);
        }
    }
    return t;
}

/**
 * Check whether this type has endless `alias this` recursion.
 *
 * Params:
 *   t = type to check whether it has a recursive alias this
 * Returns:
 *   `true` if `t` has an `alias this` that can be implicitly
 *    converted back to `t` itself.
 */
private bool checkAliasThisRec(Type t)
{
    Type tb = t.toBasetype();
    AliasThisRec* pflag;
    if (tb.ty == Tstruct)
        pflag = &(cast(TypeStruct)tb).att;
    else if (tb.ty == Tclass)
        pflag = &(cast(TypeClass)tb).att;
    else
        return false;

    AliasThisRec flag = cast(AliasThisRec)(*pflag & AliasThisRec.typeMask);
    if (flag == AliasThisRec.fwdref)
    {
        Type att = aliasthisOf(t);
        flag = att && att.implicitConvTo(t) ? AliasThisRec.yes : AliasThisRec.no;
    }
    *pflag = cast(AliasThisRec)(flag | (*pflag & ~AliasThisRec.typeMask));
    return flag == AliasThisRec.yes;
}

/**************************************
 * Check and set 'att' if 't' is a recursive 'alias this' type
 *
 * The goal is to prevent endless loops when there is a cycle in the alias this chain.
 * Since there is no multiple `alias this`, the chain either ends in a leaf,
 * or it loops back on itself as some point.
 *
 * Example: S0 -> (S1 -> S2 -> S3 -> S1)
 *
 * `S0` is not a recursive alias this, so this returns `false`, and a rewrite to `S1` can be tried.
 * `S1` is a recursive alias this type, but since `att` is initialized to `null`,
 * this still returns `false`, but `att1` is set to `S1`.
 * A rewrite to `S2` and `S3` can be tried, but when we want to try a rewrite to `S1` again,
 * we notice `att == t`, so we're back at the start of the loop, and this returns `true`.
 *
 * Params:
 *   att = type reference used to detect recursion. Should be initialized to `null`.
 *   t   = type of 'alias this' rewrite to attempt
 *
 * Returns:
 *   `false` if the rewrite is safe, `true` if it would loop back around
 */
bool isRecursiveAliasThis(ref Type att, Type t)
{
    //printf("+isRecursiveAliasThis(att = %s, t = %s)\n", att ? att.toChars() : "null", t.toChars());
    auto tb = t.toBasetype();
    if (att && tb.equivalent(att))
        return true;
    if (!att && tb.checkAliasThisRec())
        att = tb;
    return false;
}

MATCH implicitConvToWithoutAliasThis(TypeStruct from, Type to)
{
    //printf("TypeStruct::implicitConvToWithoutAliasThis(%s => %s)\n", toChars(), to.toChars());

    auto tos = to.isTypeStruct();
    if (!(tos && from.sym == tos.sym))
        return MATCH.nomatch;

    if (from.mod == to.mod)
        return MATCH.exact;

    if (MODimplicitConv(from.mod, to.mod))
        return MATCH.constant;

    /* Check all the fields. If they can all be converted,
     * allow the conversion.
     */
    MATCH m = MATCH.constant;
    uint offset = ~0; // must never match a field offset
    foreach (v; from.sym.fields[])
    {
        /* Why are we only looking at the first member of a union?
         * The check should check for overlap of v with the previous field,
         * not just starting at the same point
         */
        if (!global.params.fixImmutableConv && v.offset == offset) // v is at same offset as previous field
            continue;       // ignore

        Type tvf = v.type.addMod(from.mod);    // from type
        Type tvt  = v.type.addMod(to.mod);     // to type

        // field match
        MATCH mf = tvf.implicitConvTo(tvt);
        //printf("\t%s => %s, match = %d\n", v.type.toChars(), tvt.toChars(), mf);

        if (mf == MATCH.nomatch)
            return MATCH.nomatch;
        if (mf < m) // if field match is worse
            m = mf;
        offset = v.offset;
    }
    return m;
}

MATCH implicitConvToWithoutAliasThis(TypeClass from, Type to)
{
    ClassDeclaration cdto = to.isClassHandle();
    MATCH m = constConv(from, to);
    if (m > MATCH.nomatch)
        return m;

    if (cdto && cdto.isBaseOf(from.sym, null) && MODimplicitConv(from.mod, to.mod))
    {
        //printf("'to' is base\n");
        return MATCH.convert;
    }
    return MATCH.nomatch;
}

MATCH implicitConvToThroughAliasThis(TypeClass from, Type to)
{
    MATCH m;
    if (from.sym.aliasthis && !(from.att & AliasThisRec.tracing))
    {
        if (auto ato = aliasthisOf(from))
        {
            from.att = cast(AliasThisRec)(from.att | AliasThisRec.tracing);
            m = ato.implicitConvTo(to);
            from.att = cast(AliasThisRec)(from.att & ~AliasThisRec.tracing);
        }
    }
    return m;
}

MATCH implicitConvToThroughAliasThis(TypeStruct from, Type to)
{
    auto tos = to.isTypeStruct();
    if (!(tos && from.sym == tos.sym) &&
        from.sym.aliasthis &&
        !(from.att & AliasThisRec.tracing))
    {
        if (auto ato = aliasthisOf(from))
        {
            from.att = cast(AliasThisRec)(from.att | AliasThisRec.tracing);
            MATCH m = ato.implicitConvTo(to);
            from.att = cast(AliasThisRec)(from.att & ~AliasThisRec.tracing);
            return m;
        }
    }
    return MATCH.nomatch;
}

/*******************************************
 * Compute number of elements for a (possibly multidimensional) static array,
 * or 1 for other types.
 * Params:
 *  t = static array type
 *  loc = for error message
 * Returns:
 *  number of elements, uint.max on overflow
 */
uint numberOfElems(Type t, Loc loc)
{
    //printf("Type::numberOfElems()\n");
    uinteger_t n = 1;
    Type tb = t;
    while ((tb = tb.toBasetype()).ty == Tsarray)
    {
        bool overflow = false;
        n = mulu(n, (cast(TypeSArray)tb).dim.toUInteger(), overflow);
        if (overflow || n >= uint.max)
        {
            error(loc, "static array `%s` size overflowed to %llu", t.toChars(), cast(ulong)n);
            return uint.max;
        }
        tb = (cast(TypeSArray)tb).next;
    }
    return cast(uint)n;
}

bool checkRetType(TypeFunction tf, Loc loc)
{
    Type tb = tf.next.toBasetype();
    if (tb.ty == Tfunction)
    {
        error(loc, "functions cannot return a function");
        tf.next = Type.terror;
    }
    if (tb.ty == Ttuple)
    {
        error(loc, "functions cannot return a sequence (use `std.typecons.Tuple`)");
        tf.next = Type.terror;
    }
    if (!tf.isRef && (tb.ty == Tstruct || tb.ty == Tsarray))
    {
        if (auto ts = tb.baseElemOf().isTypeStruct())
        {
            if (!ts.sym.members)
            {
                error(loc, "functions cannot return opaque type `%s` by value", tb.toChars());
                tf.next = Type.terror;
            }
        }
    }
    if (tb.ty == Terror)
        return true;
    return false;
}

/// Returns: whether `t` is a struct/class/enum without a body
bool isOpaqueType(Type t)
{
    if (auto te = t.isTypeEnum())
        return te.sym.members is null;
    if (auto ts = t.isTypeStruct())
        return ts.sym.members is null;
    if (auto tc = t.isTypeClass())
        return tc.sym.members is null;
    return false;
}


/******************************* Private *****************************************/

private:

/* Helper function for `typeToExpression`. Contains common code
 * for TypeQualified derived classes.
 */
Expression typeToExpressionHelper(TypeQualified t, Expression e, size_t i = 0)
{
    //printf("toExpressionHelper(e = %s %s)\n", EXPtoString(e.op).ptr, e.toChars());
    foreach (id; t.idents[i .. t.idents.length])
    {
        //printf("\t[%d] e: '%s', id: '%s'\n", i, e.toChars(), id.toChars());

        final switch (id.dyncast())
        {
            // ... '. ident'
            case DYNCAST.identifier:
                e = new DotIdExp(e.loc, e, cast(Identifier)id);
                break;

            // ... '. name!(tiargs)'
            case DYNCAST.dsymbol:
                auto ti = (cast(Dsymbol)id).isTemplateInstance();
                assert(ti);
                e = new DotTemplateInstanceExp(e.loc, e, ti.name, ti.tiargs);
                break;

            // ... '[type]'
            case DYNCAST.type:          // https://issues.dlang.org/show_bug.cgi?id=1215
                e = new ArrayExp(t.loc, e, new TypeExp(t.loc, cast(Type)id));
                break;

            // ... '[expr]'
            case DYNCAST.expression:    // https://issues.dlang.org/show_bug.cgi?id=1215
                e = new ArrayExp(t.loc, e, cast(Expression)id);
                break;

            case DYNCAST.object:
            case DYNCAST.tuple:
            case DYNCAST.parameter:
            case DYNCAST.statement:
            case DYNCAST.condition:
            case DYNCAST.templateparameter:
            case DYNCAST.initializer:
                assert(0);
        }
    }
    return e;
}

/**************************
 * This evaluates exp while setting length to be the number
 * of elements in the tuple t.
 */
Expression semanticLength(Scope* sc, Type t, Expression exp)
{
    if (auto tt = t.isTypeTuple())
    {
        ScopeDsymbol sym = new ArrayScopeSymbol(sc, tt);
        sym.parent = sc.scopesym;
        sc = sc.push(sym);
        sc = sc.startCTFE();
        exp = exp.expressionSemantic(sc);
        exp = resolveProperties(sc, exp);
        sc = sc.endCTFE();
        sc.pop();
    }
    else
    {
        sc = sc.startCTFE();
        exp = exp.expressionSemantic(sc);
        exp = resolveProperties(sc, exp);
        sc = sc.endCTFE();
    }
    return exp;
}

Expression semanticLength(Scope* sc, TupleDeclaration tup, Expression exp)
{
    ScopeDsymbol sym = new ArrayScopeSymbol(sc, tup);
    sym.parent = sc.scopesym;

    sc = sc.push(sym);
    sc = sc.startCTFE();
    exp = exp.expressionSemantic(sc);
    exp = resolveProperties(sc, exp);
    sc = sc.endCTFE();
    sc.pop();

    return exp;
}

/************************************
 * Transitively search a type for all function types.
 * If any function types with parameters are found that have parameter identifiers
 * or default arguments, remove those and create a new type stripped of those.
 * This is used to determine the "canonical" version of a type which is useful for
 * comparisons.
 * Params:
 *      t = type to scan
 * Returns:
 *      `t` if no parameter identifiers or default arguments found, otherwise a new type that is
 *      the same as t but with no parameter identifiers or default arguments.
 */
Type stripDefaultArgs(Type t)
{
    static Parameters* stripParams(Parameters* parameters)
    {
        static Parameter stripParameter(Parameter p)
        {
            Type t = stripDefaultArgs(p.type);
            return (t != p.type || p.defaultArg || p.ident || p.userAttribDecl)
                ? new Parameter(p.loc, p.storageClass, t, null, null, null)
                : null;
        }

        if (parameters)
        {
            foreach (i, p; *parameters)
            {
                if (Parameter ps = stripParameter(p))
                {
                    // Replace params with a copy we can modify
                    Parameters* nparams = new Parameters(parameters.length);

                    foreach (j, ref np; *nparams)
                    {
                        Parameter pj = (*parameters)[j];
                        if (j < i)
                            np = pj;
                        else if (j == i)
                            np = ps;
                        else
                        {
                            Parameter nps = stripParameter(pj);
                            np = nps ? nps : pj;
                        }
                    }
                    return nparams;
                }
            }
        }
        return parameters;
    }

    if (t is null)
        return t;

    if (auto tf = t.isTypeFunction())
    {
        Type tret = stripDefaultArgs(tf.next);
        Parameters* params = stripParams(tf.parameterList.parameters);
        if (tret == tf.next && params == tf.parameterList.parameters)
            return t;
        TypeFunction tr = tf.copy().isTypeFunction();
        tr.parameterList.parameters = params;
        tr.next = tret;
        //printf("strip %s\n   <- %s\n", tr.toChars(), t.toChars());
        return tr;
    }
    else if (auto tt = t.isTypeTuple())
    {
        Parameters* args = stripParams(tt.arguments);
        if (args == tt.arguments)
            return t;
        TypeTuple tr = t.copy().isTypeTuple();
        tr.arguments = args;
        return tr;
    }
    else if (t.ty == Tenum)
    {
        // TypeEnum::nextOf() may be != NULL, but it's not necessary here.
        return t;
    }
    else
    {
        Type tn = t.nextOf();
        Type n = stripDefaultArgs(tn);
        if (n == tn)
            return t;
        TypeNext tr = cast(TypeNext)t.copy();
        tr.next = n;
        return tr;
    }
}

/******************************
 * Get the value of the .max/.min property of `ed` as an Expression.
 * Lazily computes the value and caches it in maxval/minval.
 * Reports any errors.
 * Params:
 *      ed = the EnumDeclaration being examined
 *      loc = location to use for error messages
 *      id = Id::max or Id::min
 * Returns:
 *      corresponding value of .max/.min
 */
Expression getMaxMinValue(EnumDeclaration ed, Loc loc, Identifier id)
{
    //printf("EnumDeclaration::getMaxValue()\n");

    static Expression pvalToResult(Expression e, Loc loc)
    {
        if (e.op != EXP.error)
        {
            e = e.copy();
            e.loc = loc;
        }
        return e;
    }

    Expression* pval = (id == Id.max) ? &ed.maxval : &ed.minval;

    Expression errorReturn()
    {
        *pval = ErrorExp.get();
        return *pval;
    }

    if (ed.inuse)
    {
        .error(loc, "%s `%s` recursive definition of `.%s` property", ed.kind, ed.toPrettyChars, id.toChars());
        return errorReturn();
    }
    if (*pval)
        return pvalToResult(*pval, loc);

    if (ed._scope)
        dsymbolSemantic(ed, ed._scope);
    if (ed.errors)
        return errorReturn();
    if (!ed.members)
    {
        .error(loc, "%s `%s` is opaque and has no `.%s`", ed.kind, ed.toPrettyChars, id.toChars(), id.toChars());
        return errorReturn();
    }
    if (!(ed.memtype && ed.memtype.isIntegral()))
    {
        .error(loc, "%s `%s` has no `.%s` property because base type `%s` is not an integral type", ed.kind, ed.toPrettyChars, id.toChars(),
              id.toChars(), ed.memtype ? ed.memtype.toChars() : "");
        return errorReturn();
    }

    bool first = true;
    for (size_t i = 0; i < ed.members.length; i++)
    {
        EnumMember em = (*ed.members)[i].isEnumMember();
        if (!em)
            continue;
        if (em.errors)
        {
            ed.errors = true;
            continue;
        }

        if (em.semanticRun < PASS.semanticdone)
        {
            .error(em.loc, "%s `%s` is forward referenced looking for `.%s`", em.kind, em.toPrettyChars, id.toChars());
            ed.errors = true;
            continue;
        }

        if (first)
        {
            *pval = em.value;
            first = false;
        }
        else
        {
            /* In order to work successfully with UDTs,
             * build expressions to do the comparisons,
             * and let the semantic analyzer and constant
             * folder give us the result.
             */

            /* Compute:
             *   if (e > maxval)
             *      maxval = e;
             */
            Expression e = em.value;
            Expression ec = new CmpExp(id == Id.max ? EXP.greaterThan : EXP.lessThan, em.loc, e, *pval);
            ed.inuse = true;
            ec = ec.expressionSemantic(em._scope);
            ed.inuse = false;
            ec = ec.ctfeInterpret();
            if (ec.op == EXP.error)
            {
                ed.errors = true;
                continue;
            }
            if (ec.toInteger())
                *pval = e;
        }
    }
    return ed.errors ? errorReturn() : pvalToResult(*pval, loc);
}

/******************************************
 * Compile the MixinType, returning the type or expression AST.
 *
 * Doesn't run semantic() on the returned object.
 * Params:
 *      tm = mixin to compile as a type or expression
 *      loc = location for error messages
 *      sc = context
 * Return:
 *      null if error, else RootObject AST as parsed
 */
RootObject compileTypeMixin(TypeMixin tm, Loc loc, Scope* sc)
{
    OutBuffer buf;
    if (expressionsToString(buf, sc, tm.exps, tm.loc, null, true))
        return null;

    const errors = global.errors;
    const len = buf.length;
    buf.writeByte(0);
    const str = buf.extractSlice()[0 .. len];
    const bool doUnittests = global.params.parsingUnittestsRequired();
    scope p = new Parser!ASTCodegen(sc._module, str, false, global.errorSink, &global.compileEnv, doUnittests);
    adjustLocForMixin(str, loc, *p.baseLoc, global.params.mixinOut);
    p.linnum = p.baseLoc.startLine;
    p.nextToken();
    //printf("p.loc.linnum = %d\n", p.loc.linnum);

    auto o = p.parseTypeOrAssignExp(TOK.endOfFile);
    if (errors != global.errors)
    {
        assert(global.errors != errors); // should have caught all these cases
        return null;
    }
    if (p.token.value != TOK.endOfFile)
    {
        .error(loc, "unexpected token `%s` after type `%s`",
            p.token.toChars(), o.toChars());
        .errorSupplemental(loc, "while parsing string mixin type `%s`",
            str.ptr);
        return null;
    }

    return o;
}
