/**
 * Compiler implementation of the
 * $(LINK2 http://www.dlang.org, D programming language).
 *
 * Copyright:   Copyright (C) 1999-2019 by The D Language Foundation, All Rights Reserved
 * Authors:     $(LINK2 http://www.digitalmars.com, Walter Bright)
 * License:     $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
 * Source:      $(LINK2 https://github.com/dlang/dmd/blob/master/src/dmd/dsymbol.d, _dsymbol.d)
 * Documentation:  https://dlang.org/phobos/dmd_dsymbol.html
 * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/dmd/dsymbol.d
 */

module dmd.dsymbol;

import core.stdc.stdarg;
import core.stdc.stdio;
import core.stdc.string;
import core.stdc.stdlib;

import dmd.aggregate;
import dmd.aliasthis;
import dmd.arraytypes;
import dmd.attrib;
import dmd.ast_node;
import dmd.gluelayer;
import dmd.dclass;
import dmd.declaration;
import dmd.denum;
import dmd.dimport;
import dmd.dmodule;
import dmd.dscope;
import dmd.dstruct;
import dmd.dsymbolsem;
import dmd.dtemplate;
import dmd.errors;
import dmd.expression;
import dmd.expressionsem;
import dmd.func;
import dmd.globals;
import dmd.id;
import dmd.identifier;
import dmd.init;
import dmd.lexer;
import dmd.mtype;
import dmd.nspace;
import dmd.opover;
import dmd.root.aav;
import dmd.root.rmem;
import dmd.root.rootobject;
import dmd.root.speller;
import dmd.statement;
import dmd.tokens;
import dmd.visitor;

/***************************************
 * Calls dg(Dsymbol *sym) for each Dsymbol.
 * If dg returns !=0, stops and returns that value else returns 0.
 * Params:
 *    symbols = Dsymbols
 *    dg = delegate to call for each Dsymbol
 * Returns:
 *    last value returned by dg()
 */
int foreachDsymbol(Dsymbols* symbols, scope int delegate(Dsymbol) dg)
{
    assert(dg);
    if (symbols)
    {
        /* Do not use foreach, as the size of the array may expand during iteration
         */
        for (size_t i = 0; i < symbols.dim; ++i)
        {
            Dsymbol s = (*symbols)[i];
            const result = dg(s);
            if (result)
                return result;
        }
    }
    return 0;
}

/***************************************
 * Calls dg(Dsymbol *sym) for each Dsymbol.
 * Params:
 *    symbols = Dsymbols
 *    dg = delegate to call for each Dsymbol
 */
void foreachDsymbol(Dsymbols* symbols, scope void delegate(Dsymbol) dg)
{
    assert(dg);
    if (symbols)
    {
        /* Do not use foreach, as the size of the array may expand during iteration
         */
        for (size_t i = 0; i < symbols.dim; ++i)
        {
            Dsymbol s = (*symbols)[i];
            dg(s);
        }
    }
}


struct Ungag
{
    uint oldgag;

    extern (D) this(uint old)
    {
        this.oldgag = old;
    }

    extern (C++) ~this()
    {
        global.gag = oldgag;
    }
}

struct Prot
{
    ///
    enum Kind : int
    {
        undefined,
        none,           // no access
        private_,
        package_,
        protected_,
        public_,
        export_,
    }

    Kind kind;
    Package pkg;

    extern (D) this(Prot.Kind kind) pure nothrow @nogc @safe
    {
        this.kind = kind;
    }

    extern (C++):

    /**
     * Checks if `this` is superset of `other` restrictions.
     * For example, "protected" is more restrictive than "public".
     */
    bool isMoreRestrictiveThan(const Prot other) const
    {
        return this.kind < other.kind;
    }

    /**
     * Checks if `this` is absolutely identical protection attribute to `other`
     */
    bool opEquals(ref const Prot other) const
    {
        if (this.kind == other.kind)
        {
            if (this.kind == Prot.Kind.package_)
                return this.pkg == other.pkg;
            return true;
        }
        return false;
    }

    /**
     * Checks if parent defines different access restrictions than this one.
     *
     * Params:
     *  parent = protection attribute for scope that hosts this one
     *
     * Returns:
     *  'true' if parent is already more restrictive than this one and thus
     *  no differentiation is needed.
     */
    bool isSubsetOf(ref const Prot parent) const
    {
        if (this.kind != parent.kind)
            return false;
        if (this.kind == Prot.Kind.package_)
        {
            if (!this.pkg)
                return true;
            if (!parent.pkg)
                return false;
            if (parent.pkg.isAncestorPackageOf(this.pkg))
                return true;
        }
        return true;
    }
}

enum PASS : int
{
    init,           // initial state
    semantic,       // semantic() started
    semanticdone,   // semantic() done
    semantic2,      // semantic2() started
    semantic2done,  // semantic2() done
    semantic3,      // semantic3() started
    semantic3done,  // semantic3() done
    inline,         // inline started
    inlinedone,     // inline done
    obj,            // toObjFile() run
}

// Search options
enum : int
{
    IgnoreNone              = 0x00, // default
    IgnorePrivateImports    = 0x01, // don't search private imports
    IgnoreErrors            = 0x02, // don't give error messages
    IgnoreAmbiguous         = 0x04, // return NULL if ambiguous
    SearchLocalsOnly        = 0x08, // only look at locals (don't search imports)
    SearchImportsOnly       = 0x10, // only look in imports
    SearchUnqualifiedModule = 0x20, // the module scope search is unqualified,
                                    // meaning don't search imports in that scope,
                                    // because qualified module searches search
                                    // their imports
    IgnoreSymbolVisibility  = 0x80, // also find private and package protected symbols
}

extern (C++) alias Dsymbol_apply_ft_t = int function(Dsymbol, void*);

/***********************************************************
 */
extern (C++) class Dsymbol : ASTNode
{
    Identifier ident;
    Dsymbol parent;
    /// C++ namespace this symbol belongs to
    CPPNamespaceDeclaration namespace;
    Symbol* csym;           // symbol for code generator
    Symbol* isym;           // import version of csym
    const(char)* comment;   // documentation comment for this Dsymbol
    const Loc loc;          // where defined
    Scope* _scope;          // !=null means context to use for semantic()
    const(char)* prettystring;  // cached value of toPrettyChars()
    bool errors;            // this symbol failed to pass semantic()
    PASS semanticRun = PASS.init;

    DeprecatedDeclaration depdecl;           // customized deprecation message
    UserAttributeDeclaration userAttribDecl;    // user defined attributes

    // !=null means there's a ddoc unittest associated with this symbol
    // (only use this with ddoc)
    UnitTestDeclaration ddocUnittest;

    final extern (D) this()
    {
        //printf("Dsymbol::Dsymbol(%p)\n", this);
        loc = Loc(null, 0, 0);
    }

    final extern (D) this(Identifier ident)
    {
        //printf("Dsymbol::Dsymbol(%p, ident)\n", this);
        this.loc = Loc(null, 0, 0);
        this.ident = ident;
    }

    final extern (D) this(const ref Loc loc, Identifier ident)
    {
        //printf("Dsymbol::Dsymbol(%p, ident)\n", this);
        this.loc = loc;
        this.ident = ident;
    }

    static Dsymbol create(Identifier ident)
    {
        return new Dsymbol(ident);
    }

    override const(char)* toChars()
    {
        return ident ? ident.toChars() : "__anonymous";
    }

    // helper to print fully qualified (template) arguments
    const(char)* toPrettyCharsHelper()
    {
        return toChars();
    }

    final const(Loc) getLoc()
    {
        if (!loc.isValid()) // avoid bug 5861.
            if (const m = getModule())
                return Loc(m.srcfile.toChars(), 0, 0);
        return loc;
    }

    final const(char)* locToChars()
    {
        return getLoc().toChars();
    }

    override bool equals(RootObject o)
    {
        if (this == o)
            return true;
        if (o.dyncast() != DYNCAST.dsymbol)
            return false;
        auto s = cast(Dsymbol)o;
        // Overload sets don't have an ident
        if (s && ident && s.ident && ident.equals(s.ident))
            return true;
        return false;
    }

    bool isAnonymous()
    {
        return ident is null;
    }

    final void error(const ref Loc loc, const(char)* format, ...)
    {
        va_list ap;
        va_start(ap, format);
        const cstr = toPrettyChars();
        const pretty = '`' ~ cstr[0 .. strlen(cstr)] ~ "`\0";
        .verror(loc, format, ap, kind(), pretty.ptr);
        va_end(ap);
    }

    final void error(const(char)* format, ...)
    {
        va_list ap;
        va_start(ap, format);
        const cstr = toPrettyChars();
        const pretty = '`' ~ cstr[0 .. strlen(cstr)] ~ "`\0";
        const loc = getLoc();
        .verror(loc, format, ap, kind(), pretty.ptr);
        va_end(ap);
    }

    final void deprecation(const ref Loc loc, const(char)* format, ...)
    {
        va_list ap;
        va_start(ap, format);
        const cstr = toPrettyChars();
        const pretty = '`' ~ cstr[0 .. strlen(cstr)] ~ "`\0";
        .vdeprecation(loc, format, ap, kind(), pretty.ptr);
        va_end(ap);
    }

    final void deprecation(const(char)* format, ...)
    {
        va_list ap;
        va_start(ap, format);
        const cstr = toPrettyChars();
        const pretty = '`' ~ cstr[0 .. strlen(cstr)] ~ "`\0";
        const loc = getLoc();
        .vdeprecation(loc, format, ap, kind(), pretty.ptr);
        va_end(ap);
    }

    final bool checkDeprecated(const ref Loc loc, Scope* sc)
    {
        if (global.params.useDeprecated != DiagnosticReporting.off && isDeprecated())
        {
            // Don't complain if we're inside a deprecated symbol's scope
            if (sc.isDeprecated())
                return false;

            const(char)* message = null;
            for (Dsymbol p = this; p; p = p.parent)
            {
                message = p.depdecl ? p.depdecl.getMessage() : null;
                if (message)
                    break;
            }
            if (message)
                deprecation(loc, "is deprecated - %s", message);
            else
                deprecation(loc, "is deprecated");

            return true;
        }

        return false;
    }

    /**********************************
     * Determine which Module a Dsymbol is in.
     */
    final Module getModule()
    {
        //printf("Dsymbol::getModule()\n");
        if (TemplateInstance ti = isInstantiated())
            return ti.tempdecl.getModule();
        Dsymbol s = this;
        while (s)
        {
            //printf("\ts = %s '%s'\n", s.kind(), s.toPrettyChars());
            Module m = s.isModule();
            if (m)
                return m;
            s = s.parent;
        }
        return null;
    }

    /**********************************
     * Determine which Module a Dsymbol is in, as far as access rights go.
     */
    final Module getAccessModule()
    {
        //printf("Dsymbol::getAccessModule()\n");
        if (TemplateInstance ti = isInstantiated())
            return ti.tempdecl.getAccessModule();
        Dsymbol s = this;
        while (s)
        {
            //printf("\ts = %s '%s'\n", s.kind(), s.toPrettyChars());
            Module m = s.isModule();
            if (m)
                return m;
            TemplateInstance ti = s.isTemplateInstance();
            if (ti && ti.enclosing)
            {
                /* Because of local template instantiation, the parent isn't where the access
                 * rights come from - it's the template declaration
                 */
                s = ti.tempdecl;
            }
            else
                s = s.parent;
        }
        return null;
    }

    /**
     * `pastMixin` returns the enclosing symbol if this is a template mixin.
     *
     * `pastMixinAndNspace` does likewise, additionally skipping over Nspaces that
     * are mangleOnly.
     *
     * See also `parent`, `toParent`, `toParent2` and `toParent3`.
     */
    final inout(Dsymbol) pastMixin() inout
    {
        //printf("Dsymbol::pastMixin() %s\n", toChars());
        if (!isTemplateMixin() && !isForwardingAttribDeclaration() && !isForwardingScopeDsymbol())
            return this;
        if (!parent)
            return null;
        return parent.pastMixin();
    }

    /// ditto
    alias pastMixinAndNspace = pastMixin;

    /**********************************
     * `parent` field returns a lexically enclosing scope symbol this is a member of.
     *
     * `toParent()` returns a logically enclosing scope symbol this is a member of.
     * It skips over TemplateMixin's and Nspaces that are mangleOnly.
     *
     * `toParent2()` returns an enclosing scope symbol this is living at runtime.
     * It skips over both TemplateInstance's and TemplateMixin's.
     * It's used when looking for the 'this' pointer of the enclosing function/class.
     *
     * `toParent3()` returns a logically enclosing scope symbol this is a member of.
     * It skips over TemplateMixin's.
     *
     * `toParentDecl()` similar to `toParent2()` but always follows the template declaration scope
     * instead of the instantiation scope.
     *
     * `toParentLocal()` similar to `toParentDecl()` but follows the instantiation scope
     * if a template declaration is non-local i.e. global or static.
     *
     * Examples:
     *  module mod;
     *  template Foo(alias a) { mixin Bar!(); }
     *  mixin template Bar() {
     *    public {  // ProtDeclaration
     *      void baz() { a = 2; }
     *    }
     *  }
     *  void test() {
     *    int v = 1;
     *    alias foo = Foo!(v);
     *    foo.baz();
     *    assert(v == 2);
     *  }
     *
     *  // s == FuncDeclaration('mod.test.Foo!().Bar!().baz()')
     *  // s.parent == TemplateMixin('mod.test.Foo!().Bar!()')
     *  // s.toParent() == TemplateInstance('mod.test.Foo!()')
     *  // s.toParent2() == FuncDeclaration('mod.test')
     *  // s.toParentDecl() == Module('mod')
     *  // s.toParentLocal() == FuncDeclaration('mod.test')
     */
    final inout(Dsymbol) toParent() inout
    {
        return parent ? parent.pastMixinAndNspace() : null;
    }

    /// ditto
    final inout(Dsymbol) toParent2() inout
    {
        if (!parent || !parent.isTemplateInstance && !parent.isForwardingAttribDeclaration() && !parent.isForwardingScopeDsymbol())
            return parent;
        return parent.toParent2;
    }

    /// ditto
    final inout(Dsymbol) toParent3() inout
    {
        return parent ? parent.pastMixin() : null;
    }

    /// ditto
    final inout(Dsymbol) toParentDecl() inout
    {
        return toParentDeclImpl(false);
    }

    /// ditto
    final inout(Dsymbol) toParentLocal() inout
    {
        return toParentDeclImpl(true);
    }

    private inout(Dsymbol) toParentDeclImpl(bool localOnly) inout
    {
        auto p = toParent();
        if (!p || !p.isTemplateInstance())
            return p;
        auto ti = p.isTemplateInstance();
        if (ti.tempdecl && (!localOnly || !(cast(TemplateDeclaration)ti.tempdecl).isstatic))
            return ti.tempdecl.toParentDeclImpl(localOnly);
        return parent.toParentDeclImpl(localOnly);
    }

    final inout(TemplateInstance) isInstantiated() inout
    {
        if (!parent)
            return null;
        auto ti = parent.isTemplateInstance();
        if (ti && !ti.isTemplateMixin())
            return ti;
        return parent.isInstantiated();
    }

    // Check if this function is a member of a template which has only been
    // instantiated speculatively, eg from inside is(typeof()).
    // Return the speculative template instance it is part of,
    // or NULL if not speculative.
    final inout(TemplateInstance) isSpeculative() inout
    {
        if (!parent)
            return null;
        auto ti = parent.isTemplateInstance();
        if (ti && ti.gagged)
            return ti;
        if (!parent.toParent())
            return null;
        return parent.isSpeculative();
    }

    final Ungag ungagSpeculative() const
    {
        uint oldgag = global.gag;
        if (global.gag && !isSpeculative() && !toParent2().isFuncDeclaration())
            global.gag = 0;
        return Ungag(oldgag);
    }

    // kludge for template.isSymbol()
    override final DYNCAST dyncast() const
    {
        return DYNCAST.dsymbol;
    }

    /*************************************
     * Do syntax copy of an array of Dsymbol's.
     */
    extern (D) static Dsymbols* arraySyntaxCopy(Dsymbols* a)
    {
        Dsymbols* b = null;
        if (a)
        {
            b = a.copy();
            for (size_t i = 0; i < b.dim; i++)
            {
                (*b)[i] = (*b)[i].syntaxCopy(null);
            }
        }
        return b;
    }

    Identifier getIdent()
    {
        return ident;
    }

    const(char)* toPrettyChars(bool QualifyTypes = false)
    {
        if (prettystring && !QualifyTypes)
            return prettystring;

        //printf("Dsymbol::toPrettyChars() '%s'\n", toChars());
        if (!parent)
        {
            auto s = toChars();
            if (!QualifyTypes)
                prettystring = s;
            return s;
        }

        // Computer number of components
        size_t complength = 0;
        for (Dsymbol p = this; p; p = p.parent)
            ++complength;

        // Allocate temporary array comp[]
        alias T = const(char)[];
        auto compptr = cast(T*)malloc(complength * T.sizeof);
        if (!compptr)
            Mem.error();
        auto comp = compptr[0 .. complength];

        // Fill in comp[] and compute length of final result
        size_t length = 0;
        int i;
        for (Dsymbol p = this; p; p = p.parent)
        {
            const s = QualifyTypes ? p.toPrettyCharsHelper() : p.toChars();
            const len = strlen(s);
            comp[i] = s[0 .. len];
            ++i;
            length += len + 1;
        }

        auto s = cast(char*)mem.xmalloc(length);
        auto q = s + length - 1;
        *q = 0;
        foreach (j; 0 .. complength)
        {
            const t = comp[j].ptr;
            const len = comp[j].length;
            q -= len;
            memcpy(q, t, len);
            if (q == s)
                break;
            *--q = '.';
        }
        free(comp.ptr);
        if (!QualifyTypes)
            prettystring = s;
        return s;
    }

    const(char)* kind() const pure nothrow @nogc @safe
    {
        return "symbol";
    }

    /*********************************
     * If this symbol is really an alias for another,
     * return that other.
     * If needed, semantic() is invoked due to resolve forward reference.
     */
    Dsymbol toAlias()
    {
        return this;
    }

    /*********************************
     * Resolve recursive tuple expansion in eponymous template.
     */
    Dsymbol toAlias2()
    {
        return toAlias();
    }

    /*********************************
     * Iterate this dsymbol or members of this scoped dsymbol, then
     * call `fp` with the found symbol and `param`.
     * Params:
     *  fp = function pointer to process the iterated symbol.
     *       If it returns nonzero, the iteration will be aborted.
     *  param = a parameter passed to fp.
     * Returns:
     *  nonzero if the iteration is aborted by the return value of fp,
     *  or 0 if it's completed.
     */
    int apply(Dsymbol_apply_ft_t fp, void* param)
    {
        return (*fp)(this, param);
    }

    void addMember(Scope* sc, ScopeDsymbol sds)
    {
        //printf("Dsymbol::addMember('%s')\n", toChars());
        //printf("Dsymbol::addMember(this = %p, '%s' scopesym = '%s')\n", this, toChars(), sds.toChars());
        //printf("Dsymbol::addMember(this = %p, '%s' sds = %p, sds.symtab = %p)\n", this, toChars(), sds, sds.symtab);
        parent = sds;
        if (!isAnonymous()) // no name, so can't add it to symbol table
        {
            if (!sds.symtabInsert(this)) // if name is already defined
            {
                Dsymbol s2 = sds.symtabLookup(this,ident);
                if (!s2.overloadInsert(this))
                {
                    sds.multiplyDefined(Loc.initial, this, s2);
                    errors = true;
                }
            }
            if (sds.isAggregateDeclaration() || sds.isEnumDeclaration())
            {
                if (ident == Id.__sizeof || ident == Id.__xalignof || ident == Id._mangleof)
                {
                    error("`.%s` property cannot be redefined", ident.toChars());
                    errors = true;
                }
            }
        }
    }

    /*************************************
     * Set scope for future semantic analysis so we can
     * deal better with forward references.
     */
    void setScope(Scope* sc)
    {
        //printf("Dsymbol::setScope() %p %s, %p stc = %llx\n", this, toChars(), sc, sc.stc);
        if (!sc.nofree)
            sc.setNoFree(); // may need it even after semantic() finishes
        _scope = sc;
        if (sc.depdecl)
            depdecl = sc.depdecl;
        if (!userAttribDecl)
            userAttribDecl = sc.userAttribDecl;
    }

    void importAll(Scope* sc)
    {
    }

    /*********************************************
     * Search for ident as member of s.
     * Params:
     *  loc = location to print for error messages
     *  ident = identifier to search for
     *  flags = IgnoreXXXX
     * Returns:
     *  null if not found
     */
    Dsymbol search(const ref Loc loc, Identifier ident, int flags = IgnoreNone)
    {
        //printf("Dsymbol::search(this=%p,%s, ident='%s')\n", this, toChars(), ident.toChars());
        return null;
    }

    final Dsymbol search_correct(Identifier ident)
    {
        /***************************************************
         * Search for symbol with correct spelling.
         */
        extern (D) Dsymbol symbol_search_fp(const(char)[] seed, ref int cost)
        {
            /* If not in the lexer's string table, it certainly isn't in the symbol table.
             * Doing this first is a lot faster.
             */
            if (!seed.length)
                return null;
            Identifier id = Identifier.lookup(seed);
            if (!id)
                return null;
            cost = 0;
            Dsymbol s = this;
            Module.clearCache();
            return s.search(Loc.initial, id, IgnoreErrors);
        }

        if (global.gag)
            return null; // don't do it for speculative compiles; too time consuming
        // search for exact name first
        if (auto s = search(Loc.initial, ident, IgnoreErrors))
            return s;
        return speller!symbol_search_fp(ident.toString());
    }

    /***************************************
     * 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 `IgnorePrivateImports`
     *
     * Returns:
     *      symbol found, NULL if not
     */
    final Dsymbol searchX(const ref Loc loc, Scope* sc, RootObject id, int flags)
    {
        //printf("Dsymbol::searchX(this=%p,%s, ident='%s')\n", this, toChars(), ident.toChars());
        Dsymbol s = 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)
                {
                    sm = s.search_correct(ti.name);
                    if (sm)
                        .error(loc, "template identifier `%s` is not a member of %s `%s`, did you mean %s `%s`?", ti.name.toChars(), s.kind(), s.toPrettyChars(), sm.kind(), sm.toChars());
                    else
                        .error(loc, "template identifier `%s` is not a member of %s `%s`", ti.name.toChars(), s.kind(), s.toPrettyChars());
                    return null;
                }
                sm = sm.toAlias();
                TemplateDeclaration td = sm.isTemplateDeclaration();
                if (!td)
                {
                    .error(loc, "`%s.%s` is not a template, it is a %s", s.toPrettyChars(), ti.name.toChars(), sm.kind());
                    return null;
                }
                ti.tempdecl = td;
                if (!ti.semanticRun)
                    ti.dsymbolSemantic(sc);
                sm = ti.toAlias();
                break;
            }
        case DYNCAST.type:
        case DYNCAST.expression:
        default:
            assert(0);
        }
        return sm;
    }

    bool overloadInsert(Dsymbol s)
    {
        //printf("Dsymbol::overloadInsert('%s')\n", s.toChars());
        return false;
    }

    /*********************************
     * Returns:
     *  SIZE_INVALID when the size cannot be determined
     */
    d_uns64 size(const ref Loc loc)
    {
        error("Dsymbol `%s` has no size", toChars());
        return SIZE_INVALID;
    }

    bool isforwardRef()
    {
        return false;
    }

    // is a 'this' required to access the member
    inout(AggregateDeclaration) isThis() inout
    {
        return null;
    }

    // is Dsymbol exported?
    bool isExport() const
    {
        return false;
    }

    // is Dsymbol imported?
    bool isImportedSymbol() const
    {
        return false;
    }

    // is Dsymbol deprecated?
    bool isDeprecated() const
    {
        return false;
    }

    bool isOverloadable() const
    {
        return false;
    }

    // is this a LabelDsymbol()?
    LabelDsymbol isLabel()
    {
        return null;
    }

    /// Returns an AggregateDeclaration when toParent() is that.
    final inout(AggregateDeclaration) isMember() inout
    {
        //printf("Dsymbol::isMember() %s\n", toChars());
        auto p = toParent();
        //printf("parent is %s %s\n", p.kind(), p.toChars());
        return p ? p.isAggregateDeclaration() : null;
    }

    /// Returns an AggregateDeclaration when toParent2() is that.
    final inout(AggregateDeclaration) isMember2() inout
    {
        //printf("Dsymbol::isMember2() '%s'\n", toChars());
        auto p = toParent2();
        //printf("parent is %s %s\n", p.kind(), p.toChars());
        return p ? p.isAggregateDeclaration() : null;
    }

    /// Returns an AggregateDeclaration when toParentDecl() is that.
    final inout(AggregateDeclaration) isMemberDecl() inout
    {
        //printf("Dsymbol::isMemberDecl() '%s'\n", toChars());
        auto p = toParentDecl();
        //printf("parent is %s %s\n", p.kind(), p.toChars());
        return p ? p.isAggregateDeclaration() : null;
    }

    /// Returns an AggregateDeclaration when toParentLocal() is that.
    final inout(AggregateDeclaration) isMemberLocal() inout
    {
        //printf("Dsymbol::isMemberLocal() '%s'\n", toChars());
        auto p = toParentLocal();
        //printf("parent is %s %s\n", p.kind(), p.toChars());
        return p ? p.isAggregateDeclaration() : null;
    }

    // is this a member of a ClassDeclaration?
    final ClassDeclaration isClassMember()
    {
        auto ad = isMember();
        return ad ? ad.isClassDeclaration() : null;
    }

    // is this a type?
    Type getType()
    {
        return null;
    }

    // need a 'this' pointer?
    bool needThis()
    {
        return false;
    }

    /*************************************
     */
    Prot prot() pure nothrow @nogc @safe
    {
        return Prot(Prot.Kind.public_);
    }

    /**************************************
     * Copy the syntax.
     * Used for template instantiations.
     * If s is NULL, allocate the new object, otherwise fill it in.
     */
    Dsymbol syntaxCopy(Dsymbol s)
    {
        printf("%s %s\n", kind(), toChars());
        assert(0);
    }

    /**************************************
     * Determine if this symbol is only one.
     * Returns:
     *      false, *ps = NULL: There are 2 or more symbols
     *      true,  *ps = NULL: There are zero symbols
     *      true,  *ps = symbol: The one and only one symbol
     */
    bool oneMember(Dsymbol* ps, Identifier ident)
    {
        //printf("Dsymbol::oneMember()\n");
        *ps = this;
        return true;
    }

    /*****************************************
     * Same as Dsymbol::oneMember(), but look at an array of Dsymbols.
     */
    extern (D) static bool oneMembers(Dsymbols* members, Dsymbol* ps, Identifier ident)
    {
        //printf("Dsymbol::oneMembers() %d\n", members ? members.dim : 0);
        Dsymbol s = null;
        if (members)
        {
            for (size_t i = 0; i < members.dim; i++)
            {
                Dsymbol sx = (*members)[i];
                bool x = sx.oneMember(ps, ident);
                //printf("\t[%d] kind %s = %d, s = %p\n", i, sx.kind(), x, *ps);
                if (!x)
                {
                    //printf("\tfalse 1\n");
                    assert(*ps is null);
                    return false;
                }
                if (*ps)
                {
                    assert(ident);
                    if (!(*ps).ident || !(*ps).ident.equals(ident))
                        continue;
                    if (!s)
                        s = *ps;
                    else if (s.isOverloadable() && (*ps).isOverloadable())
                    {
                        // keep head of overload set
                        FuncDeclaration f1 = s.isFuncDeclaration();
                        FuncDeclaration f2 = (*ps).isFuncDeclaration();
                        if (f1 && f2)
                        {
                            assert(!f1.isFuncAliasDeclaration());
                            assert(!f2.isFuncAliasDeclaration());
                            for (; f1 != f2; f1 = f1.overnext0)
                            {
                                if (f1.overnext0 is null)
                                {
                                    f1.overnext0 = f2;
                                    break;
                                }
                            }
                        }
                    }
                    else // more than one symbol
                    {
                        *ps = null;
                        //printf("\tfalse 2\n");
                        return false;
                    }
                }
            }
        }
        *ps = s; // s is the one symbol, null if none
        //printf("\ttrue\n");
        return true;
    }

    void setFieldOffset(AggregateDeclaration ad, uint* poffset, bool isunion)
    {
    }

    /*****************************************
     * Is Dsymbol a variable that contains pointers?
     */
    bool hasPointers()
    {
        //printf("Dsymbol::hasPointers() %s\n", toChars());
        return false;
    }

    bool hasStaticCtorOrDtor()
    {
        //printf("Dsymbol::hasStaticCtorOrDtor() %s\n", toChars());
        return false;
    }

    void addLocalClass(ClassDeclarations*)
    {
    }

    void addObjcSymbols(ClassDeclarations* classes, ClassDeclarations* categories)
    {
    }

    void checkCtorConstInit()
    {
    }

    /****************************************
     * Add documentation comment to Dsymbol.
     * Ignore NULL comments.
     */
    void addComment(const(char)* comment)
    {
        //if (comment)
        //    printf("adding comment '%s' to symbol %p '%s'\n", comment, this, toChars());
        if (!this.comment)
            this.comment = comment;
        else if (comment && strcmp(cast(char*)comment, cast(char*)this.comment) != 0)
        {
            // Concatenate the two
            this.comment = Lexer.combineComments(this.comment, comment, true);
        }
    }

    /****************************************
     * Returns true if this symbol is defined in a non-root module without instantiation.
     */
    final bool inNonRoot()
    {
        Dsymbol s = parent;
        for (; s; s = s.toParent())
        {
            if (auto ti = s.isTemplateInstance())
            {
                return false;
            }
            if (auto m = s.isModule())
            {
                if (!m.isRoot())
                    return true;
                break;
            }
        }
        return false;
    }

    /************
     */
    override void accept(Visitor v)
    {
        v.visit(this);
    }

  pure nothrow @safe @nogc:

    // Eliminate need for dynamic_cast
    inout(Package)                     isPackage()                     inout { return null; }
    inout(Module)                      isModule()                      inout { return null; }
    inout(EnumMember)                  isEnumMember()                  inout { return null; }
    inout(TemplateDeclaration)         isTemplateDeclaration()         inout { return null; }
    inout(TemplateInstance)            isTemplateInstance()            inout { return null; }
    inout(TemplateMixin)               isTemplateMixin()               inout { return null; }
    inout(ForwardingAttribDeclaration) isForwardingAttribDeclaration() inout { return null; }
    inout(Nspace)                      isNspace()                      inout { return null; }
    inout(Declaration)                 isDeclaration()                 inout { return null; }
    inout(StorageClassDeclaration)     isStorageClassDeclaration()     inout { return null; }
    inout(ExpressionDsymbol)           isExpressionDsymbol()           inout { return null; }
    inout(ThisDeclaration)             isThisDeclaration()             inout { return null; }
    inout(TypeInfoDeclaration)         isTypeInfoDeclaration()         inout { return null; }
    inout(TupleDeclaration)            isTupleDeclaration()            inout { return null; }
    inout(AliasDeclaration)            isAliasDeclaration()            inout { return null; }
    inout(AggregateDeclaration)        isAggregateDeclaration()        inout { return null; }
    inout(FuncDeclaration)             isFuncDeclaration()             inout { return null; }
    inout(FuncAliasDeclaration)        isFuncAliasDeclaration()        inout { return null; }
    inout(OverDeclaration)             isOverDeclaration()             inout { return null; }
    inout(FuncLiteralDeclaration)      isFuncLiteralDeclaration()      inout { return null; }
    inout(CtorDeclaration)             isCtorDeclaration()             inout { return null; }
    inout(PostBlitDeclaration)         isPostBlitDeclaration()         inout { return null; }
    inout(DtorDeclaration)             isDtorDeclaration()             inout { return null; }
    inout(StaticCtorDeclaration)       isStaticCtorDeclaration()       inout { return null; }
    inout(StaticDtorDeclaration)       isStaticDtorDeclaration()       inout { return null; }
    inout(SharedStaticCtorDeclaration) isSharedStaticCtorDeclaration() inout { return null; }
    inout(SharedStaticDtorDeclaration) isSharedStaticDtorDeclaration() inout { return null; }
    inout(InvariantDeclaration)        isInvariantDeclaration()        inout { return null; }
    inout(UnitTestDeclaration)         isUnitTestDeclaration()         inout { return null; }
    inout(NewDeclaration)              isNewDeclaration()              inout { return null; }
    inout(VarDeclaration)              isVarDeclaration()              inout { return null; }
    inout(ClassDeclaration)            isClassDeclaration()            inout { return null; }
    inout(StructDeclaration)           isStructDeclaration()           inout { return null; }
    inout(UnionDeclaration)            isUnionDeclaration()            inout { return null; }
    inout(InterfaceDeclaration)        isInterfaceDeclaration()        inout { return null; }
    inout(ScopeDsymbol)                isScopeDsymbol()                inout { return null; }
    inout(ForwardingScopeDsymbol)      isForwardingScopeDsymbol()      inout { return null; }
    inout(WithScopeSymbol)             isWithScopeSymbol()             inout { return null; }
    inout(ArrayScopeSymbol)            isArrayScopeSymbol()            inout { return null; }
    inout(Import)                      isImport()                      inout { return null; }
    inout(EnumDeclaration)             isEnumDeclaration()             inout { return null; }
    inout(DeleteDeclaration)           isDeleteDeclaration()           inout { return null; }
    inout(SymbolDeclaration)           isSymbolDeclaration()           inout { return null; }
    inout(AttribDeclaration)           isAttribDeclaration()           inout { return null; }
    inout(AnonDeclaration)             isAnonDeclaration()             inout { return null; }
    inout(CPPNamespaceDeclaration)     isCPPNamespaceDeclaration()     inout { return null; }
    inout(ProtDeclaration)             isProtDeclaration()             inout { return null; }
    inout(OverloadSet)                 isOverloadSet()                 inout { return null; }
    inout(CompileDeclaration)          isCompileDeclaration()          inout { return null; }
}

/***********************************************************
 * Dsymbol that generates a scope
 */
extern (C++) class ScopeDsymbol : Dsymbol
{
    Dsymbols* members;          // all Dsymbol's in this scope
    DsymbolTable symtab;        // members[] sorted into table
    uint endlinnum;             // the linnumber of the statement after the scope (0 if unknown)

private:
    /// symbols whose members have been imported, i.e. imported modules and template mixins
    Dsymbols* importedScopes;
    Prot.Kind* prots;            // array of Prot.Kind, one for each import

    import dmd.root.array : BitArray;
    BitArray accessiblePackages, privateAccessiblePackages;// whitelists of accessible (imported) packages

public:
    final extern (D) this()
    {
    }

    final extern (D) this(Identifier ident)
    {
        super(ident);
    }

    final extern (D) this(const ref Loc loc, Identifier ident)
    {
        super(loc, ident);
    }

    override Dsymbol syntaxCopy(Dsymbol s)
    {
        //printf("ScopeDsymbol::syntaxCopy('%s')\n", toChars());
        ScopeDsymbol sds = s ? cast(ScopeDsymbol)s : new ScopeDsymbol(ident);
        sds.members = arraySyntaxCopy(members);
        sds.endlinnum = endlinnum;
        return sds;
    }

    /*****************************************
     * This function is #1 on the list of functions that eat cpu time.
     * Be very, very careful about slowing it down.
     */
    override Dsymbol search(const ref Loc loc, Identifier ident, int flags = SearchLocalsOnly)
    {
        //printf("%s.ScopeDsymbol::search(ident='%s', flags=x%x)\n", toChars(), ident.toChars(), flags);
        //if (strcmp(ident.toChars(),"c") == 0) *(char*)0=0;

        // Look in symbols declared in this module
        if (symtab && !(flags & SearchImportsOnly))
        {
            //printf(" look in locals\n");
            auto s1 = symtab.lookup(ident);
            if (s1)
            {
                //printf("\tfound in locals = '%s.%s'\n",toChars(),s1.toChars());
                return s1;
            }
        }
        //printf(" not found in locals\n");

        // Look in imported scopes
        if (!importedScopes)
            return null;

        //printf(" look in imports\n");
        Dsymbol s = null;
        OverloadSet a = null;
        // Look in imported modules
        for (size_t i = 0; i < importedScopes.dim; i++)
        {
            // If private import, don't search it
            if ((flags & IgnorePrivateImports) && prots[i] == Prot.Kind.private_)
                continue;
            int sflags = flags & (IgnoreErrors | IgnoreAmbiguous); // remember these in recursive searches
            Dsymbol ss = (*importedScopes)[i];
            //printf("\tscanning import '%s', prots = %d, isModule = %p, isImport = %p\n", ss.toChars(), prots[i], ss.isModule(), ss.isImport());

            if (ss.isModule())
            {
                if (flags & SearchLocalsOnly)
                    continue;
            }
            else // mixin template
            {
                if (flags & SearchImportsOnly)
                    continue;

                sflags |= SearchLocalsOnly;
            }

            /* Don't find private members if ss is a module
             */
            Dsymbol s2 = ss.search(loc, ident, sflags | (ss.isModule() ? IgnorePrivateImports : IgnoreNone));
            import dmd.access : symbolIsVisible;
            if (!s2 || !(flags & IgnoreSymbolVisibility) && !symbolIsVisible(this, s2))
                continue;
            if (!s)
            {
                s = s2;
                if (s && s.isOverloadSet())
                    a = mergeOverloadSet(ident, a, s);
            }
            else if (s2 && s != s2)
            {
                if (s.toAlias() == s2.toAlias() || s.getType() == s2.getType() && s.getType())
                {
                    /* After following aliases, we found the same
                     * symbol, so it's not an ambiguity.  But if one
                     * alias is deprecated or less accessible, prefer
                     * the other.
                     */
                    if (s.isDeprecated() || s.prot().isMoreRestrictiveThan(s2.prot()) && s2.prot().kind != Prot.Kind.none)
                        s = s2;
                }
                else
                {
                    /* Two imports of the same module should be regarded as
                     * the same.
                     */
                    Import i1 = s.isImport();
                    Import i2 = s2.isImport();
                    if (!(i1 && i2 && (i1.mod == i2.mod || (!i1.parent.isImport() && !i2.parent.isImport() && i1.ident.equals(i2.ident)))))
                    {
                        /* https://issues.dlang.org/show_bug.cgi?id=8668
                         * Public selective import adds AliasDeclaration in module.
                         * To make an overload set, resolve aliases in here and
                         * get actual overload roots which accessible via s and s2.
                         */
                        s = s.toAlias();
                        s2 = s2.toAlias();
                        /* If both s2 and s are overloadable (though we only
                         * need to check s once)
                         */

                        if ((s2.isOverloadSet() || s2.isOverloadable()) && (a || s.isOverloadable()))
                        {
                            if (symbolIsVisible(this, s2))
                            {
                                a = mergeOverloadSet(ident, a, s2);
                            }
                            if (!symbolIsVisible(this, s))
                                s = s2;
                            continue;
                        }
                        if (flags & IgnoreAmbiguous) // if return NULL on ambiguity
                            return null;
                        if (!(flags & IgnoreErrors))
                            ScopeDsymbol.multiplyDefined(loc, s, s2);
                        break;
                    }
                }
            }
        }
        if (s)
        {
            /* Build special symbol if we had multiple finds
             */
            if (a)
            {
                if (!s.isOverloadSet())
                    a = mergeOverloadSet(ident, a, s);
                s = a;
            }
            //printf("\tfound in imports %s.%s\n", toChars(), s.toChars());
            return s;
        }
        //printf(" not found in imports\n");
        return null;
    }

    final OverloadSet mergeOverloadSet(Identifier ident, OverloadSet os, Dsymbol s)
    {
        if (!os)
        {
            os = new OverloadSet(ident);
            os.parent = this;
        }
        if (OverloadSet os2 = s.isOverloadSet())
        {
            // Merge the cross-module overload set 'os2' into 'os'
            if (os.a.dim == 0)
            {
                os.a.setDim(os2.a.dim);
                memcpy(os.a.tdata(), os2.a.tdata(), (os.a[0]).sizeof * os2.a.dim);
            }
            else
            {
                for (size_t i = 0; i < os2.a.dim; i++)
                {
                    os = mergeOverloadSet(ident, os, os2.a[i]);
                }
            }
        }
        else
        {
            assert(s.isOverloadable());
            /* Don't add to os[] if s is alias of previous sym
             */
            for (size_t j = 0; j < os.a.dim; j++)
            {
                Dsymbol s2 = os.a[j];
                if (s.toAlias() == s2.toAlias())
                {
                    if (s2.isDeprecated() || (s2.prot().isMoreRestrictiveThan(s.prot()) && s.prot().kind != Prot.Kind.none))
                    {
                        os.a[j] = s;
                    }
                    goto Lcontinue;
                }
            }
            os.push(s);
        Lcontinue:
        }
        return os;
    }

    void importScope(Dsymbol s, Prot protection)
    {
        //printf("%s.ScopeDsymbol::importScope(%s, %d)\n", toChars(), s.toChars(), protection);
        // No circular or redundant import's
        if (s != this)
        {
            if (!importedScopes)
                importedScopes = new Dsymbols();
            else
            {
                for (size_t i = 0; i < importedScopes.dim; i++)
                {
                    Dsymbol ss = (*importedScopes)[i];
                    if (ss == s) // if already imported
                    {
                        if (protection.kind > prots[i])
                            prots[i] = protection.kind; // upgrade access
                        return;
                    }
                }
            }
            importedScopes.push(s);
            prots = cast(Prot.Kind*)mem.xrealloc(prots, importedScopes.dim * (prots[0]).sizeof);
            prots[importedScopes.dim - 1] = protection.kind;
        }
    }

    final void addAccessiblePackage(Package p, Prot protection)
    {
        // https://issues.dlang.org/show_bug.cgi?id=17991
        // An import of truly empty file/package can happen
        if (p is null)
            return;
        auto pary = protection.kind == Prot.Kind.private_ ? &privateAccessiblePackages : &accessiblePackages;
        if (pary.length <= p.tag)
            pary.length = p.tag + 1;
        (*pary)[p.tag] = true;
    }

    bool isPackageAccessible(Package p, Prot protection, int flags = 0)
    {
        if (p.tag < accessiblePackages.length && accessiblePackages[p.tag] ||
            protection.kind == Prot.Kind.private_ && p.tag < privateAccessiblePackages.length && privateAccessiblePackages[p.tag])
            return true;
        foreach (i, ss; importedScopes ? (*importedScopes)[] : null)
        {
            // only search visible scopes && imported modules should ignore private imports
            if (protection.kind <= prots[i] &&
                ss.isScopeDsymbol.isPackageAccessible(p, protection, IgnorePrivateImports))
                return true;
        }
        return false;
    }

    override final bool isforwardRef()
    {
        return (members is null);
    }

    static void multiplyDefined(const ref Loc loc, Dsymbol s1, Dsymbol s2)
    {
        version (none)
        {
            printf("ScopeDsymbol::multiplyDefined()\n");
            printf("s1 = %p, '%s' kind = '%s', parent = %s\n", s1, s1.toChars(), s1.kind(), s1.parent ? s1.parent.toChars() : "");
            printf("s2 = %p, '%s' kind = '%s', parent = %s\n", s2, s2.toChars(), s2.kind(), s2.parent ? s2.parent.toChars() : "");
        }
        if (loc.isValid())
        {
            .error(loc, "`%s` at %s conflicts with `%s` at %s", s1.toPrettyChars(), s1.locToChars(), s2.toPrettyChars(), s2.locToChars());
        }
        else
        {
            s1.error(s1.loc, "conflicts with %s `%s` at %s", s2.kind(), s2.toPrettyChars(), s2.locToChars());
        }
    }

    override const(char)* kind() const
    {
        return "ScopeDsymbol";
    }

    /*******************************************
     * Look for member of the form:
     *      const(MemberInfo)[] getMembers(string);
     * Returns NULL if not found
     */
    final FuncDeclaration findGetMembers()
    {
        Dsymbol s = search_function(this, Id.getmembers);
        FuncDeclaration fdx = s ? s.isFuncDeclaration() : null;
        version (none)
        {
            // Finish
            __gshared TypeFunction tfgetmembers;
            if (!tfgetmembers)
            {
                Scope sc;
                auto parameters = new Parameters();
                Parameters* p = new Parameter(STC.in_, Type.tchar.constOf().arrayOf(), null, null);
                parameters.push(p);
                Type tret = null;
                tfgetmembers = new TypeFunction(parameters, tret, VarArg.none, LINK.d);
                tfgetmembers = cast(TypeFunction)tfgetmembers.dsymbolSemantic(Loc.initial, &sc);
            }
            if (fdx)
                fdx = fdx.overloadExactMatch(tfgetmembers);
        }
        if (fdx && fdx.isVirtual())
            fdx = null;
        return fdx;
    }

    Dsymbol symtabInsert(Dsymbol s)
    {
        return symtab.insert(s);
    }

    /****************************************
     * Look up identifier in symbol table.
     */

    Dsymbol symtabLookup(Dsymbol s, Identifier id)
    {
        return symtab.lookup(id);
    }

    /****************************************
     * Return true if any of the members are static ctors or static dtors, or if
     * any members have members that are.
     */
    override bool hasStaticCtorOrDtor()
    {
        if (members)
        {
            for (size_t i = 0; i < members.dim; i++)
            {
                Dsymbol member = (*members)[i];
                if (member.hasStaticCtorOrDtor())
                    return true;
            }
        }
        return false;
    }

    extern (D) alias ForeachDg = int delegate(size_t idx, Dsymbol s);

    /***************************************
     * Expands attribute declarations in members in depth first
     * order. Calls dg(size_t symidx, Dsymbol *sym) for each
     * member.
     * If dg returns !=0, stops and returns that value else returns 0.
     * Use this function to avoid the O(N + N^2/2) complexity of
     * calculating dim and calling N times getNth.
     * Returns:
     *  last value returned by dg()
     */
    extern (D) static int _foreach(Scope* sc, Dsymbols* members, scope ForeachDg dg, size_t* pn = null)
    {
        assert(dg);
        if (!members)
            return 0;
        size_t n = pn ? *pn : 0; // take over index
        int result = 0;
        foreach (size_t i; 0 .. members.dim)
        {
            Dsymbol s = (*members)[i];
            if (AttribDeclaration a = s.isAttribDeclaration())
                result = _foreach(sc, a.include(sc), dg, &n);
            else if (TemplateMixin tm = s.isTemplateMixin())
                result = _foreach(sc, tm.members, dg, &n);
            else if (s.isTemplateInstance())
            {
            }
            else if (s.isUnitTestDeclaration())
            {
            }
            else
                result = dg(n++, s);
            if (result)
                break;
        }
        if (pn)
            *pn = n; // update index
        return result;
    }

    override final inout(ScopeDsymbol) isScopeDsymbol() inout
    {
        return this;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/***********************************************************
 * With statement scope
 */
extern (C++) final class WithScopeSymbol : ScopeDsymbol
{
    WithStatement withstate;

    extern (D) this(WithStatement withstate)
    {
        this.withstate = withstate;
    }

    override Dsymbol search(const ref Loc loc, Identifier ident, int flags = SearchLocalsOnly)
    {
        //printf("WithScopeSymbol.search(%s)\n", ident.toChars());
        if (flags & SearchImportsOnly)
            return null;
        // Acts as proxy to the with class declaration
        Dsymbol s = null;
        Expression eold = null;
        for (Expression e = withstate.exp; e != eold; e = resolveAliasThis(_scope, e))
        {
            if (e.op == TOK.scope_)
            {
                s = (cast(ScopeExp)e).sds;
            }
            else if (e.op == TOK.type)
            {
                s = e.type.toDsymbol(null);
            }
            else
            {
                Type t = e.type.toBasetype();
                s = t.toDsymbol(null);
            }
            if (s)
            {
                s = s.search(loc, ident, flags);
                if (s)
                    return s;
            }
            eold = e;
        }
        return null;
    }

    override inout(WithScopeSymbol) isWithScopeSymbol() inout
    {
        return this;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/***********************************************************
 * Array Index/Slice scope
 */
extern (C++) final class ArrayScopeSymbol : ScopeDsymbol
{
    Expression exp;         // IndexExp or SliceExp
    TypeTuple type;         // for tuple[length]
    TupleDeclaration td;    // for tuples of objects
    Scope* sc;

    extern (D) this(Scope* sc, Expression exp)
    {
        super(exp.loc, null);
        assert(exp.op == TOK.index || exp.op == TOK.slice || exp.op == TOK.array);
        this.exp = exp;
        this.sc = sc;
    }

    extern (D) this(Scope* sc, TypeTuple type)
    {
        this.type = type;
        this.sc = sc;
    }

    extern (D) this(Scope* sc, TupleDeclaration td)
    {
        this.td = td;
        this.sc = sc;
    }

    override Dsymbol search(const ref Loc loc, Identifier ident, int flags = IgnoreNone)
    {
        //printf("ArrayScopeSymbol::search('%s', flags = %d)\n", ident.toChars(), flags);
        if (ident != Id.dollar)
            return null;

        VarDeclaration* pvar;
        Expression ce;
    L1:
        if (td)
        {
            /* $ gives the number of elements in the tuple
             */
            auto v = new VarDeclaration(loc, Type.tsize_t, Id.dollar, null);
            Expression e = new IntegerExp(Loc.initial, td.objects.dim, Type.tsize_t);
            v._init = new ExpInitializer(Loc.initial, e);
            v.storage_class |= STC.temp | STC.static_ | STC.const_;
            v.dsymbolSemantic(sc);
            return v;
        }
        if (type)
        {
            /* $ gives the number of type entries in the type tuple
             */
            auto v = new VarDeclaration(loc, Type.tsize_t, Id.dollar, null);
            Expression e = new IntegerExp(Loc.initial, type.arguments.dim, Type.tsize_t);
            v._init = new ExpInitializer(Loc.initial, e);
            v.storage_class |= STC.temp | STC.static_ | STC.const_;
            v.dsymbolSemantic(sc);
            return v;
        }
        if (exp.op == TOK.index)
        {
            /* array[index] where index is some function of $
             */
            IndexExp ie = cast(IndexExp)exp;
            pvar = &ie.lengthVar;
            ce = ie.e1;
        }
        else if (exp.op == TOK.slice)
        {
            /* array[lwr .. upr] where lwr or upr is some function of $
             */
            SliceExp se = cast(SliceExp)exp;
            pvar = &se.lengthVar;
            ce = se.e1;
        }
        else if (exp.op == TOK.array)
        {
            /* array[e0, e1, e2, e3] where e0, e1, e2 are some function of $
             * $ is a opDollar!(dim)() where dim is the dimension(0,1,2,...)
             */
            ArrayExp ae = cast(ArrayExp)exp;
            pvar = &ae.lengthVar;
            ce = ae.e1;
        }
        else
        {
            /* Didn't find $, look in enclosing scope(s).
             */
            return null;
        }
        while (ce.op == TOK.comma)
            ce = (cast(CommaExp)ce).e2;
        /* If we are indexing into an array that is really a type
         * tuple, rewrite this as an index into a type tuple and
         * try again.
         */
        if (ce.op == TOK.type)
        {
            Type t = (cast(TypeExp)ce).type;
            if (t.ty == Ttuple)
            {
                type = cast(TypeTuple)t;
                goto L1;
            }
        }
        /* *pvar is lazily initialized, so if we refer to $
         * multiple times, it gets set only once.
         */
        if (!*pvar) // if not already initialized
        {
            /* Create variable v and set it to the value of $
             */
            VarDeclaration v;
            Type t;
            if (ce.op == TOK.tuple)
            {
                /* It is for an expression tuple, so the
                 * length will be a const.
                 */
                Expression e = new IntegerExp(Loc.initial, (cast(TupleExp)ce).exps.dim, Type.tsize_t);
                v = new VarDeclaration(loc, Type.tsize_t, Id.dollar, new ExpInitializer(Loc.initial, e));
                v.storage_class |= STC.temp | STC.static_ | STC.const_;
            }
            else if (ce.type && (t = ce.type.toBasetype()) !is null && (t.ty == Tstruct || t.ty == Tclass))
            {
                // Look for opDollar
                assert(exp.op == TOK.array || exp.op == TOK.slice);
                AggregateDeclaration ad = isAggregate(t);
                assert(ad);
                Dsymbol s = ad.search(loc, Id.opDollar);
                if (!s) // no dollar exists -- search in higher scope
                    return null;
                s = s.toAlias();
                Expression e = null;
                // Check for multi-dimensional opDollar(dim) template.
                if (TemplateDeclaration td = s.isTemplateDeclaration())
                {
                    dinteger_t dim = 0;
                    if (exp.op == TOK.array)
                    {
                        dim = (cast(ArrayExp)exp).currentDimension;
                    }
                    else if (exp.op == TOK.slice)
                    {
                        dim = 0; // slices are currently always one-dimensional
                    }
                    else
                    {
                        assert(0);
                    }
                    auto tiargs = new Objects();
                    Expression edim = new IntegerExp(Loc.initial, dim, Type.tsize_t);
                    edim = edim.expressionSemantic(sc);
                    tiargs.push(edim);
                    e = new DotTemplateInstanceExp(loc, ce, td.ident, tiargs);
                }
                else
                {
                    /* opDollar exists, but it's not a template.
                     * This is acceptable ONLY for single-dimension indexing.
                     * Note that it's impossible to have both template & function opDollar,
                     * because both take no arguments.
                     */
                    if (exp.op == TOK.array && (cast(ArrayExp)exp).arguments.dim != 1)
                    {
                        exp.error("`%s` only defines opDollar for one dimension", ad.toChars());
                        return null;
                    }
                    Declaration d = s.isDeclaration();
                    assert(d);
                    e = new DotVarExp(loc, ce, d);
                }
                e = e.expressionSemantic(sc);
                if (!e.type)
                    exp.error("`%s` has no value", e.toChars());
                t = e.type.toBasetype();
                if (t && t.ty == Tfunction)
                    e = new CallExp(e.loc, e);
                v = new VarDeclaration(loc, null, Id.dollar, new ExpInitializer(Loc.initial, e));
                v.storage_class |= STC.temp | STC.ctfe | STC.rvalue;
            }
            else
            {
                /* For arrays, $ will either be a compile-time constant
                 * (in which case its value in set during constant-folding),
                 * or a variable (in which case an expression is created in
                 * toir.c).
                 */
                auto e = new VoidInitializer(Loc.initial);
                e.type = Type.tsize_t;
                v = new VarDeclaration(loc, Type.tsize_t, Id.dollar, e);
                v.storage_class |= STC.temp | STC.ctfe; // it's never a true static variable
            }
            *pvar = v;
        }
        (*pvar).dsymbolSemantic(sc);
        return (*pvar);
    }

    override inout(ArrayScopeSymbol) isArrayScopeSymbol() inout
    {
        return this;
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/***********************************************************
 * Overload Sets
 */
extern (C++) final class OverloadSet : Dsymbol
{
    Dsymbols a;     // array of Dsymbols

    extern (D) this(Identifier ident, OverloadSet os = null)
    {
        super(ident);
        if (os)
        {
            a.pushSlice(os.a[]);
        }
    }

    void push(Dsymbol s)
    {
        a.push(s);
    }

    override inout(OverloadSet) isOverloadSet() inout
    {
        return this;
    }

    override const(char)* kind() const
    {
        return "overloadset";
    }

    override void accept(Visitor v)
    {
        v.visit(this);
    }
}

/***********************************************************
 * Forwarding ScopeDsymbol.  Used by ForwardingAttribDeclaration and
 * ForwardingScopeDeclaration to forward symbol insertions to another
 * scope.  See `dmd.attrib.ForwardingAttribDeclaration` for more
 * details.
 */
extern (C++) final class ForwardingScopeDsymbol : ScopeDsymbol
{
    /*************************
     * Symbol to forward insertions to.
     * Can be `null` before being lazily initialized.
     */
    ScopeDsymbol forward;
    extern (D) this(ScopeDsymbol forward)
    {
        super(null);
        this.forward = forward;
    }
    override Dsymbol symtabInsert(Dsymbol s)
    {
        assert(forward);
        if (auto d = s.isDeclaration())
        {
            if (d.storage_class & STC.local)
            {
                // Symbols with storage class STC.local are not
                // forwarded, but stored in the local symbol
                // table. (Those are the `static foreach` variables.)
                if (!symtab)
                {
                    symtab = new DsymbolTable();
                }
                return super.symtabInsert(s); // insert locally
            }
        }
        if (!forward.symtab)
        {
            forward.symtab = new DsymbolTable();
        }
        // Non-STC.local symbols are forwarded to `forward`.
        return forward.symtabInsert(s);
    }

    /************************
     * This override handles the following two cases:
     *     static foreach (i, i; [0]) { ... }
     * and
     *     static foreach (i; [0]) { enum i = 2; }
     */
    override Dsymbol symtabLookup(Dsymbol s, Identifier id)
    {
        assert(forward);
        // correctly diagnose clashing foreach loop variables.
        if (auto d = s.isDeclaration())
        {
            if (d.storage_class & STC.local)
            {
                if (!symtab)
                {
                    symtab = new DsymbolTable();
                }
                return super.symtabLookup(s,id);
            }
        }
        // Declarations within `static foreach` do not clash with
        // `static foreach` loop variables.
        if (!forward.symtab)
        {
            forward.symtab = new DsymbolTable();
        }
        return forward.symtabLookup(s,id);
    }

    override void importScope(Dsymbol s, Prot protection)
    {
        forward.importScope(s, protection);
    }

    override const(char)* kind()const{ return "local scope"; }

    override inout(ForwardingScopeDsymbol) isForwardingScopeDsymbol() inout
    {
        return this;
    }

}

/**
 * Class that holds an expression in a Dsymbol wraper.
 * This is not an AST node, but a class used to pass
 * an expression as a function parameter of type Dsymbol.
 */
extern (C++) final class ExpressionDsymbol : Dsymbol
{
    Expression exp;
    this(Expression exp)
    {
        super();
        this.exp = exp;
    }

    override inout(ExpressionDsymbol) isExpressionDsymbol() inout
    {
        return this;
    }
}


/***********************************************************
 * Table of Dsymbol's
 */
extern (C++) final class DsymbolTable : RootObject
{
    AssocArray!(Identifier, Dsymbol) tab;

    // Look up Identifier. Return Dsymbol if found, NULL if not.
    Dsymbol lookup(const Identifier ident)
    {
        //printf("DsymbolTable::lookup(%s)\n", ident.toChars());
        return tab[ident];
    }

    // Insert Dsymbol in table. Return NULL if already there.
    Dsymbol insert(Dsymbol s)
    {
        //printf("DsymbolTable::insert(this = %p, '%s')\n", this, s.ident.toChars());
        return insert(s.ident, s);
    }

    // Look for Dsymbol in table. If there, return it. If not, insert s and return that.
    Dsymbol update(Dsymbol s)
    {
        const ident = s.ident;
        Dsymbol* ps = tab.getLvalue(ident);
        *ps = s;
        return s;
    }

    // when ident and s are not the same
    Dsymbol insert(const Identifier ident, Dsymbol s)
    {
        //printf("DsymbolTable::insert()\n");
        Dsymbol* ps = tab.getLvalue(ident);
        if (*ps)
            return null; // already in table
        *ps = s;
        return s;
    }

    /*****
     * Returns:
     *  number of symbols in symbol table
     */
    uint len() const pure
    {
        return cast(uint)tab.length;
    }
}
