xref: /src/external/gpl3/gcc.old/dist/gcc/d/dmd/declaration.d

/**
 * Miscellaneous declarations, including typedef, alias, variable declarations including the
 * implicit this declaration, type tuples, ClassInfo, ModuleInfo and various TypeInfos.
 *
 * Copyright:   Copyright (C) 1999-2022 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/declaration.d, _declaration.d)
 * Documentation:  https://dlang.org/phobos/dmd_declaration.html
 * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/dmd/declaration.d
 */

module dmd.declaration;

import core.stdc.stdio;
import dmd.aggregate;
import dmd.arraytypes;
import dmd.astenums;
import dmd.attrib;
import dmd.ctorflow;
import dmd.dclass;
import dmd.delegatize;
import dmd.dscope;
import dmd.dstruct;
import dmd.dsymbol;
import dmd.dsymbolsem;
import dmd.dtemplate;
import dmd.errors;
import dmd.expression;
import dmd.func;
import dmd.globals;
import dmd.gluelayer;
import dmd.id;
import dmd.identifier;
import dmd.init;
import dmd.initsem;
import dmd.intrange;
import dmd.mtype;
import dmd.common.outbuffer;
import dmd.root.rootobject;
import dmd.target;
import dmd.tokens;
import dmd.typesem;
import dmd.visitor;

/************************************
 * Check to see the aggregate type is nested and its context pointer is
 * accessible from the current scope.
 * Returns true if error occurs.
 */
bool checkFrameAccess(Loc loc, Scope* sc, AggregateDeclaration ad, size_t iStart = 0)
{
    Dsymbol sparent = ad.toParentLocal();
    Dsymbol sparent2 = ad.toParent2();
    Dsymbol s = sc.func;
    if (ad.isNested() && s)
    {
        //printf("ad = %p %s [%s], parent:%p\n", ad, ad.toChars(), ad.loc.toChars(), ad.parent);
        //printf("sparent = %p %s [%s], parent: %s\n", sparent, sparent.toChars(), sparent.loc.toChars(), sparent.parent,toChars());
        //printf("sparent2 = %p %s [%s], parent: %s\n", sparent2, sparent2.toChars(), sparent2.loc.toChars(), sparent2.parent,toChars());
        if (!ensureStaticLinkTo(s, sparent) || sparent != sparent2 && !ensureStaticLinkTo(s, sparent2))
        {
            error(loc, "cannot access frame pointer of `%s`", ad.toPrettyChars());
            return true;
        }
    }

    bool result = false;
    for (size_t i = iStart; i < ad.fields.dim; i++)
    {
        VarDeclaration vd = ad.fields[i];
        Type tb = vd.type.baseElemOf();
        if (tb.ty == Tstruct)
        {
            result |= checkFrameAccess(loc, sc, (cast(TypeStruct)tb).sym);
        }
    }
    return result;
}

/***********************************************
 * Mark variable v as modified if it is inside a constructor that var
 * is a field in.
 */
bool modifyFieldVar(Loc loc, Scope* sc, VarDeclaration var, Expression e1)
{
    //printf("modifyFieldVar(var = %s)\n", var.toChars());
    Dsymbol s = sc.func;
    while (1)
    {
        FuncDeclaration fd = null;
        if (s)
            fd = s.isFuncDeclaration();
        if (fd &&
            ((fd.isCtorDeclaration() && var.isField()) ||
             (fd.isStaticCtorDeclaration() && !var.isField())) &&
            fd.toParentDecl() == var.toParent2() &&
            (!e1 || e1.op == EXP.this_))
        {
            bool result = true;

            var.ctorinit = true;
            //printf("setting ctorinit\n");

            if (var.isField() && sc.ctorflow.fieldinit.length && !sc.intypeof)
            {
                assert(e1);
                auto mustInit = ((var.storage_class & STC.nodefaultctor) != 0 ||
                                 var.type.needsNested());

                const dim = sc.ctorflow.fieldinit.length;
                auto ad = fd.isMemberDecl();
                assert(ad);
                size_t i;
                for (i = 0; i < dim; i++) // same as findFieldIndexByName in ctfeexp.c ?
                {
                    if (ad.fields[i] == var)
                        break;
                }
                assert(i < dim);
                auto fieldInit = &sc.ctorflow.fieldinit[i];
                const fi = fieldInit.csx;

                if (fi & CSX.this_ctor)
                {
                    if (var.type.isMutable() && e1.type.isMutable())
                        result = false;
                    else
                    {
                        const(char)* modStr = !var.type.isMutable() ? MODtoChars(var.type.mod) : MODtoChars(e1.type.mod);
                        .error(loc, "%s field `%s` initialized multiple times", modStr, var.toChars());
                        .errorSupplemental(fieldInit.loc, "Previous initialization is here.");
                    }
                }
                else if (sc.inLoop || (fi & CSX.label))
                {
                    if (!mustInit && var.type.isMutable() && e1.type.isMutable())
                        result = false;
                    else
                    {
                        const(char)* modStr = !var.type.isMutable() ? MODtoChars(var.type.mod) : MODtoChars(e1.type.mod);
                        .error(loc, "%s field `%s` initialization is not allowed in loops or after labels", modStr, var.toChars());
                    }
                }

                fieldInit.csx |= CSX.this_ctor;
                fieldInit.loc = e1.loc;
                if (var.overlapped) // https://issues.dlang.org/show_bug.cgi?id=15258
                {
                    foreach (j, v; ad.fields)
                    {
                        if (v is var || !var.isOverlappedWith(v))
                            continue;
                        v.ctorinit = true;
                        sc.ctorflow.fieldinit[j].csx = CSX.this_ctor;
                    }
                }
            }
            else if (fd != sc.func)
            {
                if (var.type.isMutable())
                    result = false;
                else if (sc.func.fes)
                {
                    const(char)* p = var.isField() ? "field" : var.kind();
                    .error(loc, "%s %s `%s` initialization is not allowed in foreach loop",
                        MODtoChars(var.type.mod), p, var.toChars());
                }
                else
                {
                    const(char)* p = var.isField() ? "field" : var.kind();
                    .error(loc, "%s %s `%s` initialization is not allowed in nested function `%s`",
                        MODtoChars(var.type.mod), p, var.toChars(), sc.func.toChars());
                }
            }
            else if (fd.isStaticCtorDeclaration() && !fd.isSharedStaticCtorDeclaration() &&
                     var.type.isImmutable())
            {
                .error(loc, "%s %s `%s` initialization is not allowed in `static this`",
                    MODtoChars(var.type.mod), var.kind(), var.toChars());
                errorSupplemental(loc, "Use `shared static this` instead.");
            }
            return result;
        }
        else
        {
            if (s)
            {
                s = s.toParentP(var.toParent2());
                continue;
            }
        }
        break;
    }
    return false;
}

/******************************************
 */
extern (C++) void ObjectNotFound(Identifier id)
{
    error(Loc.initial, "`%s` not found. object.d may be incorrectly installed or corrupt.", id.toChars());
    fatal();
}

/* Accumulator for successive matches.
 */
struct MatchAccumulator
{
    int count;              // number of matches found so far
    MATCH last = MATCH.nomatch; // match level of lastf
    FuncDeclaration lastf;  // last matching function we found
    FuncDeclaration nextf;  // if ambiguous match, this is the "other" function
}

/***********************************************************
 */
extern (C++) abstract class Declaration : Dsymbol
{
    Type type;
    Type originalType;  // before semantic analysis
    StorageClass storage_class = STC.undefined_;
    Visibility visibility;
    LINK _linkage = LINK.default_; // may be `LINK.system`; use `resolvedLinkage()` to resolve it
    short inuse;          // used to detect cycles

    ubyte adFlags;         // control re-assignment of AliasDeclaration (put here for packing reasons)
      enum wasRead    = 1; // set if AliasDeclaration was read
      enum ignoreRead = 2; // ignore any reads of AliasDeclaration

    Symbol* isym;           // import version of csym

    // overridden symbol with pragma(mangle, "...")
    const(char)[] mangleOverride;

    final extern (D) this(Identifier ident)
    {
        super(ident);
        visibility = Visibility(Visibility.Kind.undefined);
    }

    final extern (D) this(const ref Loc loc, Identifier ident)
    {
        super(loc, ident);
        visibility = Visibility(Visibility.Kind.undefined);
    }

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

    override final uinteger_t size(const ref Loc loc)
    {
        assert(type);
        const sz = type.size();
        if (sz == SIZE_INVALID)
            errors = true;
        return sz;
    }

    /**
     * Issue an error if an attempt to call a disabled method is made
     *
     * If the declaration is disabled but inside a disabled function,
     * returns `true` but do not issue an error message.
     *
     * Params:
     *   loc = Location information of the call
     *   sc  = Scope in which the call occurs
     *   isAliasedDeclaration = if `true` searches overload set
     *
     * Returns:
     *   `true` if this `Declaration` is `@disable`d, `false` otherwise.
     */
    extern (D) final bool checkDisabled(Loc loc, Scope* sc, bool isAliasedDeclaration = false)
    {
        if (!(storage_class & STC.disable))
            return false;

        if (sc.func && sc.func.storage_class & STC.disable)
            return true;

        if (auto p = toParent())
        {
            if (auto postblit = isPostBlitDeclaration())
            {
                /* https://issues.dlang.org/show_bug.cgi?id=21885
                 *
                 * If the generated postblit is disabled, it
                 * means that one of the fields has a disabled
                 * postblit. Print the first field that has
                 * a disabled postblit.
                 */
                if (postblit.isGenerated())
                {
                    auto sd = p.isStructDeclaration();
                    assert(sd);
                    for (size_t i = 0; i < sd.fields.dim; i++)
                    {
                        auto structField = sd.fields[i];
                        if (structField.overlapped)
                            continue;
                        Type tv = structField.type.baseElemOf();
                        if (tv.ty != Tstruct)
                            continue;
                        auto sdv = (cast(TypeStruct)tv).sym;
                        if (!sdv.postblit)
                            continue;
                        if (sdv.postblit.isDisabled())
                        {
                            p.error(loc, "is not copyable because field `%s` is not copyable", structField.toChars());
                            return true;
                        }
                    }
                }
                p.error(loc, "is not copyable because it has a disabled postblit");
                return true;
            }
        }

        // if the function is @disabled, maybe there
        // is an overload in the overload set that isn't
        if (isAliasedDeclaration)
        {
            FuncDeclaration fd = isFuncDeclaration();
            if (fd)
            {
                for (FuncDeclaration ovl = fd; ovl; ovl = cast(FuncDeclaration)ovl.overnext)
                    if (!(ovl.storage_class & STC.disable))
                        return false;
            }
        }

        if (auto ctor = isCtorDeclaration())
        {
            if (ctor.isCpCtor && ctor.isGenerated())
            {
                .error(loc, "Generating an `inout` copy constructor for `struct %s` failed, therefore instances of it are uncopyable", parent.toPrettyChars());
                return true;
            }
        }
        error(loc, "cannot be used because it is annotated with `@disable`");
        return true;
    }

    /*************************************
     * Check to see if declaration can be modified in this context (sc).
     * Issue error if not.
     * Params:
     *  loc  = location for error messages
     *  e1   = `null` or `this` expression when this declaration is a field
     *  sc   = context
     *  flag = if the first bit is set it means do not issue error message for
     *         invalid modification; if the second bit is set, it means that
               this declaration is a field and a subfield of it is modified.
     * Returns:
     *  Modifiable.yes or Modifiable.initialization
     */
    extern (D) final Modifiable checkModify(Loc loc, Scope* sc, Expression e1, ModifyFlags flag)
    {
        VarDeclaration v = isVarDeclaration();
        if (v && v.canassign)
            return Modifiable.initialization;

        if (isParameter() || isResult())
        {
            for (Scope* scx = sc; scx; scx = scx.enclosing)
            {
                if (scx.func == parent && (scx.flags & SCOPE.contract))
                {
                    const(char)* s = isParameter() && parent.ident != Id.ensure ? "parameter" : "result";
                    if (!(flag & ModifyFlags.noError))
                        error(loc, "cannot modify %s `%s` in contract", s, toChars());
                    return Modifiable.initialization; // do not report type related errors
                }
            }
        }

        if (e1 && e1.op == EXP.this_ && isField())
        {
            VarDeclaration vthis = e1.isThisExp().var;
            for (Scope* scx = sc; scx; scx = scx.enclosing)
            {
                if (scx.func == vthis.parent && (scx.flags & SCOPE.contract))
                {
                    if (!(flag & ModifyFlags.noError))
                        error(loc, "cannot modify parameter `this` in contract");
                    return Modifiable.initialization; // do not report type related errors
                }
            }
        }

        if (v && (v.isCtorinit() || isField()))
        {
            // It's only modifiable if inside the right constructor
            if ((storage_class & (STC.foreach_ | STC.ref_)) == (STC.foreach_ | STC.ref_))
                return Modifiable.initialization;
            if (flag & ModifyFlags.fieldAssign)
                return Modifiable.yes;
            return modifyFieldVar(loc, sc, v, e1) ? Modifiable.initialization : Modifiable.yes;
        }
        return Modifiable.yes;
    }

    override final Dsymbol search(const ref Loc loc, Identifier ident, int flags = SearchLocalsOnly)
    {
        Dsymbol s = Dsymbol.search(loc, ident, flags);
        if (!s && type)
        {
            s = type.toDsymbol(_scope);
            if (s)
                s = s.search(loc, ident, flags);
        }
        return s;
    }

    final bool isStatic() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.static_) != 0;
    }

    /// Returns the linkage, resolving the target-specific `System` one.
    final LINK resolvedLinkage() const
    {
        return _linkage == LINK.system ? target.systemLinkage() : _linkage;
    }

    bool isDelete()
    {
        return false;
    }

    bool isDataseg()
    {
        return false;
    }

    bool isThreadlocal()
    {
        return false;
    }

    bool isCodeseg() const pure nothrow @nogc @safe
    {
        return false;
    }

    final bool isFinal() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.final_) != 0;
    }

    bool isAbstract()
    {
        return (storage_class & STC.abstract_) != 0;
    }

    final bool isConst() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.const_) != 0;
    }

    final bool isImmutable() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.immutable_) != 0;
    }

    final bool isWild() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.wild) != 0;
    }

    final bool isAuto() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.auto_) != 0;
    }

    final bool isScope() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.scope_) != 0;
    }

    final bool isSynchronized() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.synchronized_) != 0;
    }

    final bool isParameter() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.parameter) != 0;
    }

    override final bool isDeprecated() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.deprecated_) != 0;
    }

    final bool isDisabled() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.disable) != 0;
    }

    final bool isOverride() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.override_) != 0;
    }

    final bool isResult() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.result) != 0;
    }

    final bool isField() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.field) != 0;
    }

    final bool isIn() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.in_) != 0;
    }

    final bool isOut() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.out_) != 0;
    }

    final bool isRef() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.ref_) != 0;
    }

    /// Returns: Whether the variable is a reference, annotated with `out` or `ref`
    final bool isReference() const pure nothrow @nogc @safe
    {
        return (storage_class & (STC.ref_ | STC.out_)) != 0;
    }

    final bool isFuture() const pure nothrow @nogc @safe
    {
        return (storage_class & STC.future) != 0;
    }

    override final Visibility visible() pure nothrow @nogc @safe
    {
        return visibility;
    }

    override final inout(Declaration) isDeclaration() inout pure nothrow @nogc @safe
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) final class TupleDeclaration : Declaration
{
    Objects* objects;
    bool isexp;             // true: expression tuple
    TypeTuple tupletype;    // !=null if this is a type tuple

    extern (D) this(const ref Loc loc, Identifier ident, Objects* objects)
    {
        super(loc, ident);
        this.objects = objects;
    }

    override TupleDeclaration syntaxCopy(Dsymbol s)
    {
        assert(0);
    }

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

    override Type getType()
    {
        /* If this tuple represents a type, return that type
         */

        //printf("TupleDeclaration::getType() %s\n", toChars());
        if (isexp)
            return null;
        if (!tupletype)
        {
            /* It's only a type tuple if all the Object's are types
             */
            for (size_t i = 0; i < objects.dim; i++)
            {
                RootObject o = (*objects)[i];
                if (o.dyncast() != DYNCAST.type)
                {
                    //printf("\tnot[%d], %p, %d\n", i, o, o.dyncast());
                    return null;
                }
            }

            /* We know it's a type tuple, so build the TypeTuple
             */
            Types* types = cast(Types*)objects;
            auto args = new Parameters(objects.dim);
            OutBuffer buf;
            int hasdeco = 1;
            for (size_t i = 0; i < types.dim; i++)
            {
                Type t = (*types)[i];
                //printf("type = %s\n", t.toChars());
                version (none)
                {
                    buf.printf("_%s_%d", ident.toChars(), i);
                    const len = buf.offset;
                    const name = buf.extractSlice().ptr;
                    auto id = Identifier.idPool(name, len);
                    auto arg = new Parameter(STC.in_, t, id, null);
                }
                else
                {
                    auto arg = new Parameter(0, t, null, null, null);
                }
                (*args)[i] = arg;
                if (!t.deco)
                    hasdeco = 0;
            }

            tupletype = new TypeTuple(args);
            if (hasdeco)
                return tupletype.typeSemantic(Loc.initial, null);
        }
        return tupletype;
    }

    override Dsymbol toAlias2()
    {
        //printf("TupleDeclaration::toAlias2() '%s' objects = %s\n", toChars(), objects.toChars());
        for (size_t i = 0; i < objects.dim; i++)
        {
            RootObject o = (*objects)[i];
            if (Dsymbol s = isDsymbol(o))
            {
                s = s.toAlias2();
                (*objects)[i] = s;
            }
        }
        return this;
    }

    override bool needThis()
    {
        //printf("TupleDeclaration::needThis(%s)\n", toChars());
        return isexp ? foreachVar((s) { return s.needThis(); }) != 0 : false;
    }

    /***********************************************************
     * Calls dg(Dsymbol) for each Dsymbol, which should be a VarDeclaration
     * inside DsymbolExp (isexp == true).
     * Params:
     *    dg = delegate to call for each Dsymbol
     */
    extern (D) void foreachVar(scope void delegate(Dsymbol) dg)
    {
        assert(isexp);
        foreach (o; *objects)
        {
            if (auto e = o.isExpression())
                if (auto se = e.isDsymbolExp())
                    dg(se.s);
        }
    }

    /***********************************************************
     * Calls dg(Dsymbol) for each Dsymbol, which should be a VarDeclaration
     * inside DsymbolExp (isexp == true).
     * If dg returns !=0, stops and returns that value else returns 0.
     * Params:
     *    dg = delegate to call for each Dsymbol
     * Returns:
     *    last value returned by dg()
     */
    extern (D) int foreachVar(scope int delegate(Dsymbol) dg)
    {
        assert(isexp);
        foreach (o; *objects)
        {
            if (auto e = o.isExpression())
                if (auto se = e.isDsymbolExp())
                    if(auto ret = dg(se.s))
                        return ret;
        }
        return 0;
    }

    override inout(TupleDeclaration) isTupleDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 * https://dlang.org/spec/declaration.html#AliasDeclaration
 */
extern (C++) final class AliasDeclaration : Declaration
{
    Dsymbol aliassym;   // alias ident = aliassym;

    Dsymbol overnext;   // next in overload list
    Dsymbol _import;    // !=null if unresolved internal alias for selective import

    extern (D) this(const ref Loc loc, Identifier ident, Type type)
    {
        super(loc, ident);
        //printf("AliasDeclaration(id = '%s', type = %p)\n", id.toChars(), type);
        //printf("type = '%s'\n", type.toChars());
        this.type = type;
        assert(type);
    }

    extern (D) this(const ref Loc loc, Identifier ident, Dsymbol s)
    {
        super(loc, ident);
        //printf("AliasDeclaration(id = '%s', s = %p)\n", id.toChars(), s);
        assert(s != this);
        this.aliassym = s;
        assert(s);
    }

    static AliasDeclaration create(const ref Loc loc, Identifier id, Type type)
    {
        return new AliasDeclaration(loc, id, type);
    }

    override AliasDeclaration syntaxCopy(Dsymbol s)
    {
        //printf("AliasDeclaration::syntaxCopy()\n");
        assert(!s);
        AliasDeclaration sa = type ? new AliasDeclaration(loc, ident, type.syntaxCopy()) : new AliasDeclaration(loc, ident, aliassym.syntaxCopy(null));
        sa.comment = comment;
        sa.storage_class = storage_class;
        return sa;
    }

    override bool overloadInsert(Dsymbol s)
    {
        //printf("[%s] AliasDeclaration::overloadInsert('%s') s = %s %s @ [%s]\n",
        //       loc.toChars(), toChars(), s.kind(), s.toChars(), s.loc.toChars());

        /** Aliases aren't overloadable themselves, but if their Aliasee is
         *  overloadable they are converted to an overloadable Alias (either
         *  FuncAliasDeclaration or OverDeclaration).
         *
         *  This is done by moving the Aliasee into such an overloadable alias
         *  which is then used to replace the existing Aliasee. The original
         *  Alias (_this_) remains a useless shell.
         *
         *  This is a horrible mess. It was probably done to avoid replacing
         *  existing AST nodes and references, but it needs a major
         *  simplification b/c it's too complex to maintain.
         *
         *  A simpler approach might be to merge any colliding symbols into a
         *  simple Overload class (an array) and then later have that resolve
         *  all collisions.
         */
        if (semanticRun >= PASS.semanticdone)
        {
            /* Semantic analysis is already finished, and the aliased entity
             * is not overloadable.
             */
            if (type)
                return false;

            /* When s is added in member scope by static if, mixin("code") or others,
             * aliassym is determined already. See the case in: test/compilable/test61.d
             */
            auto sa = aliassym.toAlias();

            if (auto td = s.toAlias().isTemplateDeclaration())
                s = td.funcroot ? td.funcroot : td;

            if (auto fd = sa.isFuncDeclaration())
            {
                auto fa = new FuncAliasDeclaration(ident, fd);
                fa.visibility = visibility;
                fa.parent = parent;
                aliassym = fa;
                return aliassym.overloadInsert(s);
            }
            if (auto td = sa.isTemplateDeclaration())
            {
                auto od = new OverDeclaration(ident, td.funcroot ? td.funcroot : td);
                od.visibility = visibility;
                od.parent = parent;
                aliassym = od;
                return aliassym.overloadInsert(s);
            }
            if (auto od = sa.isOverDeclaration())
            {
                if (sa.ident != ident || sa.parent != parent)
                {
                    od = new OverDeclaration(ident, od);
                    od.visibility = visibility;
                    od.parent = parent;
                    aliassym = od;
                }
                return od.overloadInsert(s);
            }
            if (auto os = sa.isOverloadSet())
            {
                if (sa.ident != ident || sa.parent != parent)
                {
                    os = new OverloadSet(ident, os);
                    // TODO: visibility is lost here b/c OverloadSets have no visibility attribute
                    // Might no be a practical issue, b/c the code below fails to resolve the overload anyhow.
                    // ----
                    // module os1;
                    // import a, b;
                    // private alias merged = foo; // private alias to overload set of a.foo and b.foo
                    // ----
                    // module os2;
                    // import a, b;
                    // public alias merged = bar; // public alias to overload set of a.bar and b.bar
                    // ----
                    // module bug;
                    // import os1, os2;
                    // void test() { merged(123); } // should only look at os2.merged
                    //
                    // os.visibility = visibility;
                    os.parent = parent;
                    aliassym = os;
                }
                os.push(s);
                return true;
            }
            return false;
        }

        /* Don't know yet what the aliased symbol is, so assume it can
         * be overloaded and check later for correctness.
         */
        if (overnext)
            return overnext.overloadInsert(s);
        if (s is this)
            return true;
        overnext = s;
        return true;
    }

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

    override Type getType()
    {
        if (type)
            return type;
        return toAlias().getType();
    }

    override Dsymbol toAlias()
    {
        //printf("[%s] AliasDeclaration::toAlias('%s', this = %p, aliassym = %p, kind = '%s', inuse = %d)\n",
        //    loc.toChars(), toChars(), this, aliassym, aliassym ? aliassym.kind() : "", inuse);
        assert(this != aliassym);
        //static int count; if (++count == 10) *(char*)0=0;

        // Reading the AliasDeclaration
        if (!(adFlags & ignoreRead))
            adFlags |= wasRead;                 // can never assign to this AliasDeclaration again

        if (inuse == 1 && type && _scope)
        {
            inuse = 2;
            uint olderrors = global.errors;
            Dsymbol s = type.toDsymbol(_scope);
            //printf("[%s] type = %s, s = %p, this = %p\n", loc.toChars(), type.toChars(), s, this);
            if (global.errors != olderrors)
                goto Lerr;
            if (s)
            {
                s = s.toAlias();
                if (global.errors != olderrors)
                    goto Lerr;
                aliassym = s;
                inuse = 0;
            }
            else
            {
                Type t = type.typeSemantic(loc, _scope);
                if (t.ty == Terror)
                    goto Lerr;
                if (global.errors != olderrors)
                    goto Lerr;
                //printf("t = %s\n", t.toChars());
                inuse = 0;
            }
        }
        if (inuse)
        {
            error("recursive alias declaration");

        Lerr:
            // Avoid breaking "recursive alias" state during errors gagged
            if (global.gag)
                return this;
            aliassym = new AliasDeclaration(loc, ident, Type.terror);
            type = Type.terror;
            return aliassym;
        }

        if (semanticRun >= PASS.semanticdone)
        {
            // semantic is already done.

            // Do not see aliassym !is null, because of lambda aliases.

            // Do not see type.deco !is null, even so "alias T = const int;` needs
            // semantic analysis to take the storage class `const` as type qualifier.
        }
        else
        {
            if (_import && _import._scope)
            {
                /* If this is an internal alias for selective/renamed import,
                 * load the module first.
                 */
                _import.dsymbolSemantic(null);
            }
            if (_scope)
            {
                aliasSemantic(this, _scope);
            }
        }

        inuse = 1;
        Dsymbol s = aliassym ? aliassym.toAlias() : this;
        inuse = 0;
        return s;
    }

    override Dsymbol toAlias2()
    {
        if (inuse)
        {
            error("recursive alias declaration");
            return this;
        }
        inuse = 1;
        Dsymbol s = aliassym ? aliassym.toAlias2() : this;
        inuse = 0;
        return s;
    }

    override bool isOverloadable() const
    {
        // assume overloadable until alias is resolved
        return semanticRun < PASS.semanticdone ||
            aliassym && aliassym.isOverloadable();
    }

    override inout(AliasDeclaration) isAliasDeclaration() inout
    {
        return this;
    }

    /** Returns: `true` if this instance was created to make a template parameter
    visible in the scope of a template body, `false` otherwise */
    extern (D) bool isAliasedTemplateParameter() const
    {
        return !!(storage_class & STC.templateparameter);
    }

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

/***********************************************************
 */
extern (C++) final class OverDeclaration : Declaration
{
    Dsymbol overnext;   // next in overload list
    Dsymbol aliassym;

    extern (D) this(Identifier ident, Dsymbol s)
    {
        super(ident);
        this.aliassym = s;
    }

    override const(char)* kind() const
    {
        return "overload alias"; // todo
    }

    override bool equals(const RootObject o) const
    {
        if (this == o)
            return true;

        auto s = isDsymbol(o);
        if (!s)
            return false;

        if (auto od2 = s.isOverDeclaration())
            return this.aliassym.equals(od2.aliassym);
        return this.aliassym == s;
    }

    override bool overloadInsert(Dsymbol s)
    {
        //printf("OverDeclaration::overloadInsert('%s') aliassym = %p, overnext = %p\n", s.toChars(), aliassym, overnext);
        if (overnext)
            return overnext.overloadInsert(s);
        if (s == this)
            return true;
        overnext = s;
        return true;
    }

    override bool isOverloadable() const
    {
        return true;
    }

    Dsymbol isUnique()
    {
        Dsymbol result = null;
        overloadApply(aliassym, (Dsymbol s)
        {
            if (result)
            {
                result = null;
                return 1; // ambiguous, done
            }
            else
            {
                result = s;
                return 0;
            }
        });
        return result;
    }

    override inout(OverDeclaration) isOverDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) class VarDeclaration : Declaration
{
    Initializer _init;
    FuncDeclarations nestedrefs;    // referenced by these lexically nested functions
    Dsymbol aliassym;               // if redone as alias to another symbol
    VarDeclaration lastVar;         // Linked list of variables for goto-skips-init detection
    Expression edtor;               // if !=null, does the destruction of the variable
    IntRange* range;                // if !=null, the variable is known to be within the range
    VarDeclarations* maybes;        // STC.maybescope variables that are assigned to this STC.maybescope variable

    uint endlinnum;                 // line number of end of scope that this var lives in
    uint offset;
    uint sequenceNumber;            // order the variables are declared
    structalign_t alignment;

    // When interpreting, these point to the value (NULL if value not determinable)
    // The index of this variable on the CTFE stack, AdrOnStackNone if not allocated
    enum AdrOnStackNone = ~0u;
    uint ctfeAdrOnStack;

    // `bool` fields that are compacted into bit fields in a string mixin
    private extern (D) static struct BitFields
    {
        bool isargptr;          /// if parameter that _argptr points to
        bool ctorinit;          /// it has been initialized in a ctor
        bool iscatchvar;        /// this is the exception object variable in catch() clause
        bool isowner;           /// this is an Owner, despite it being `scope`
        bool setInCtorOnly;     /// field can only be set in a constructor, as it is const or immutable

        /// It is a class that was allocated on the stack
        ///
        /// This means the var is not rebindable once assigned,
        /// and the destructor gets run when it goes out of scope
        bool onstack;

        bool overlapped;        /// if it is a field and has overlapping
        bool overlapUnsafe;     /// if it is an overlapping field and the overlaps are unsafe
        bool doNotInferScope;   /// do not infer 'scope' for this variable
        bool doNotInferReturn;  /// do not infer 'return' for this variable

        bool isArgDtorVar;      /// temporary created to handle scope destruction of a function argument
    }

    import dmd.common.bitfields : generateBitFields;
    mixin(generateBitFields!(BitFields, ushort));

    byte canassign;                 // it can be assigned to
    ubyte isdataseg;                // private data for isDataseg 0 unset, 1 true, 2 false

    final extern (D) this(const ref Loc loc, Type type, Identifier ident, Initializer _init, StorageClass storage_class = STC.undefined_)
    in
    {
        assert(ident);
    }
    do
    {
        //printf("VarDeclaration('%s')\n", ident.toChars());
        super(loc, ident);
        debug
        {
            if (!type && !_init)
            {
                //printf("VarDeclaration('%s')\n", ident.toChars());
                //*(char*)0=0;
            }
        }

        assert(type || _init);
        this.type = type;
        this._init = _init;
        ctfeAdrOnStack = AdrOnStackNone;
        this.storage_class = storage_class;
    }

    static VarDeclaration create(const ref Loc loc, Type type, Identifier ident, Initializer _init, StorageClass storage_class = STC.undefined_)
    {
        return new VarDeclaration(loc, type, ident, _init, storage_class);
    }

    override VarDeclaration syntaxCopy(Dsymbol s)
    {
        //printf("VarDeclaration::syntaxCopy(%s)\n", toChars());
        assert(!s);
        auto v = new VarDeclaration(loc, type ? type.syntaxCopy() : null, ident, _init ? _init.syntaxCopy() : null, storage_class);
        v.comment = comment;
        return v;
    }

    override void setFieldOffset(AggregateDeclaration ad, ref FieldState fieldState, bool isunion)
    {
        //printf("VarDeclaration::setFieldOffset(ad = %s) %s\n", ad.toChars(), toChars());

        if (aliassym)
        {
            // If this variable was really a tuple, set the offsets for the tuple fields
            TupleDeclaration v2 = aliassym.isTupleDeclaration();
            assert(v2);
            v2.foreachVar((s) { s.setFieldOffset(ad, fieldState, isunion); });
            return;
        }

        if (!isField())
            return;
        assert(!(storage_class & (STC.static_ | STC.extern_ | STC.parameter)));

        //printf("+VarDeclaration::setFieldOffset(ad = %s) %s\n", ad.toChars(), toChars());

        /* Fields that are tuples appear both as part of TupleDeclarations and
         * as members. That means ignore them if they are already a field.
         */
        if (offset)
        {
            // already a field
            fieldState.offset = ad.structsize; // https://issues.dlang.org/show_bug.cgi?id=13613
            return;
        }
        for (size_t i = 0; i < ad.fields.dim; i++)
        {
            if (ad.fields[i] == this)
            {
                // already a field
                fieldState.offset = ad.structsize; // https://issues.dlang.org/show_bug.cgi?id=13613
                return;
            }
        }

        // Check for forward referenced types which will fail the size() call
        Type t = type.toBasetype();
        if (storage_class & STC.ref_)
        {
            // References are the size of a pointer
            t = Type.tvoidptr;
        }
        Type tv = t.baseElemOf();
        if (tv.ty == Tstruct)
        {
            auto ts = cast(TypeStruct)tv;
            assert(ts.sym != ad);   // already checked in ad.determineFields()
            if (!ts.sym.determineSize(loc))
            {
                type = Type.terror;
                errors = true;
                return;
            }
        }

        // List in ad.fields. Even if the type is error, it's necessary to avoid
        // pointless error diagnostic "more initializers than fields" on struct literal.
        ad.fields.push(this);

        if (t.ty == Terror)
            return;

        /* If coming after a bit field in progress,
         * advance past the field
         */
        fieldState.inFlight = false;

        const sz = t.size(loc);
        assert(sz != SIZE_INVALID && sz < uint.max);
        uint memsize = cast(uint)sz;                // size of member
        uint memalignsize = target.fieldalign(t);   // size of member for alignment purposes
        offset = AggregateDeclaration.placeField(
            &fieldState.offset,
            memsize, memalignsize, alignment,
            &ad.structsize, &ad.alignsize,
            isunion);

        //printf("\t%s: memalignsize = %d\n", toChars(), memalignsize);
        //printf(" addField '%s' to '%s' at offset %d, size = %d\n", toChars(), ad.toChars(), offset, memsize);
    }

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

    override final inout(AggregateDeclaration) isThis() inout
    {
        if (!(storage_class & (STC.static_ | STC.extern_ | STC.manifest | STC.templateparameter | STC.gshared | STC.ctfe)))
        {
            /* The casting is necessary because `s = s.parent` is otherwise rejected
             */
            for (auto s = cast(Dsymbol)this; s; s = s.parent)
            {
                auto ad = (cast(inout)s).isMember();
                if (ad)
                    return ad;
                if (!s.parent || !s.parent.isTemplateMixin())
                    break;
            }
        }
        return null;
    }

    override final bool needThis()
    {
        //printf("VarDeclaration::needThis(%s, x%x)\n", toChars(), storage_class);
        return isField();
    }

    override final bool isExport() const
    {
        return visibility.kind == Visibility.Kind.export_;
    }

    override final bool isImportedSymbol() const
    {
        if (visibility.kind == Visibility.Kind.export_ && !_init && (storage_class & STC.static_ || parent.isModule()))
            return true;
        return false;
    }

    final bool isCtorinit() const pure nothrow @nogc @safe
    {
        return setInCtorOnly;
    }

    /*******************************
     * Does symbol go into data segment?
     * Includes extern variables.
     */
    override final bool isDataseg()
    {
        version (none)
        {
            printf("VarDeclaration::isDataseg(%p, '%s')\n", this, toChars());
            printf("%llx, isModule: %p, isTemplateInstance: %p, isNspace: %p\n",
                   storage_class & (STC.static_ | STC.const_), parent.isModule(), parent.isTemplateInstance(), parent.isNspace());
            printf("parent = '%s'\n", parent.toChars());
        }

        if (isdataseg == 0) // the value is not cached
        {
            isdataseg = 2; // The Variables does not go into the datasegment

            if (!canTakeAddressOf())
            {
                return false;
            }

            Dsymbol parent = toParent();
            if (!parent && !(storage_class & STC.static_))
            {
                error("forward referenced");
                type = Type.terror;
            }
            else if (storage_class & (STC.static_ | STC.extern_ | STC.gshared) ||
                parent.isModule() || parent.isTemplateInstance() || parent.isNspace())
            {
                assert(!isParameter() && !isResult());
                isdataseg = 1; // It is in the DataSegment
            }
        }

        return (isdataseg == 1);
    }
    /************************************
     * Does symbol go into thread local storage?
     */
    override final bool isThreadlocal()
    {
        //printf("VarDeclaration::isThreadlocal(%p, '%s')\n", this, toChars());
        /* Data defaults to being thread-local. It is not thread-local
         * if it is immutable, const or shared.
         */
        bool i = isDataseg() && !(storage_class & (STC.immutable_ | STC.const_ | STC.shared_ | STC.gshared));
        //printf("\treturn %d\n", i);
        return i;
    }

    /********************************************
     * Can variable be read and written by CTFE?
     */
    final bool isCTFE()
    {
        return (storage_class & STC.ctfe) != 0; // || !isDataseg();
    }

    final bool isOverlappedWith(VarDeclaration v)
    {
        const vsz = v.type.size();
        const tsz = type.size();
        assert(vsz != SIZE_INVALID && tsz != SIZE_INVALID);

        // Overlap is checked by comparing bit offsets
        auto bitoffset  =   offset * 8;
        auto vbitoffset = v.offset * 8;

        // Bitsize of types are overridden by any bit-field widths.
        ulong tbitsize = void;
        if (auto bf = isBitFieldDeclaration())
        {
            bitoffset += bf.bitOffset;
            tbitsize = bf.fieldWidth;
        }
        else
            tbitsize = tsz * 8;

        ulong vbitsize = void;
        if (auto vbf = v.isBitFieldDeclaration())
        {
            vbitoffset += vbf.bitOffset;
            vbitsize = vbf.fieldWidth;
        }
        else
            vbitsize = vsz * 8;

        return   bitoffset < vbitoffset + vbitsize &&
                vbitoffset <  bitoffset + tbitsize;
    }

    override final bool hasPointers()
    {
        //printf("VarDeclaration::hasPointers() %s, ty = %d\n", toChars(), type.ty);
        return (!isDataseg() && type.hasPointers());
    }

    /*************************************
     * Return true if we can take the address of this variable.
     */
    final bool canTakeAddressOf()
    {
        return !(storage_class & STC.manifest);
    }

    /******************************************
     * Return true if variable needs to call the destructor.
     */
    final bool needsScopeDtor()
    {
        //printf("VarDeclaration::needsScopeDtor() %s\n", toChars());
        return edtor && !(storage_class & STC.nodtor);
    }

    /******************************************
     * If a variable has a scope destructor call, return call for it.
     * Otherwise, return NULL.
     */
    extern (D) final Expression callScopeDtor(Scope* sc)
    {
        //printf("VarDeclaration::callScopeDtor() %s\n", toChars());

        // Destruction of STC.field's is handled by buildDtor()
        if (storage_class & (STC.nodtor | STC.ref_ | STC.out_ | STC.field))
        {
            return null;
        }

        if (iscatchvar)
            return null;    // destructor is built by `void semantic(Catch c, Scope* sc)`, not here

        Expression e = null;
        // Destructors for structs and arrays of structs
        Type tv = type.baseElemOf();
        if (tv.ty == Tstruct)
        {
            StructDeclaration sd = (cast(TypeStruct)tv).sym;
            if (!sd.dtor || sd.errors)
                return null;

            const sz = type.size();
            assert(sz != SIZE_INVALID);
            if (!sz)
                return null;

            if (type.toBasetype().ty == Tstruct)
            {
                // v.__xdtor()
                e = new VarExp(loc, this);

                /* This is a hack so we can call destructors on const/immutable objects.
                 * Need to add things like "const ~this()" and "immutable ~this()" to
                 * fix properly.
                 */
                e.type = e.type.mutableOf();

                // Enable calling destructors on shared objects.
                // The destructor is always a single, non-overloaded function,
                // and must serve both shared and non-shared objects.
                e.type = e.type.unSharedOf;

                e = new DotVarExp(loc, e, sd.dtor, false);
                e = new CallExp(loc, e);
            }
            else
            {
                // __ArrayDtor(v[0 .. n])
                e = new VarExp(loc, this);

                const sdsz = sd.type.size();
                assert(sdsz != SIZE_INVALID && sdsz != 0);
                const n = sz / sdsz;
                SliceExp se = new SliceExp(loc, e, new IntegerExp(loc, 0, Type.tsize_t),
                    new IntegerExp(loc, n, Type.tsize_t));

                // Prevent redundant bounds check
                se.upperIsInBounds = true;
                se.lowerIsLessThanUpper = true;

                // This is a hack so we can call destructors on const/immutable objects.
                se.type = sd.type.arrayOf();

                e = new CallExp(loc, new IdentifierExp(loc, Id.__ArrayDtor), se);
            }
            return e;
        }
        // Destructors for classes
        if (storage_class & (STC.auto_ | STC.scope_) && !(storage_class & STC.parameter))
        {
            for (ClassDeclaration cd = type.isClassHandle(); cd; cd = cd.baseClass)
            {
                /* We can do better if there's a way with onstack
                 * classes to determine if there's no way the monitor
                 * could be set.
                 */
                //if (cd.isInterfaceDeclaration())
                //    error("interface `%s` cannot be scope", cd.toChars());

                if (onstack) // if any destructors
                {
                    // delete'ing C++ classes crashes (and delete is deprecated anyway)
                    if (cd.classKind == ClassKind.cpp)
                    {
                        // Don't call non-existant dtor
                        if (!cd.dtor)
                            break;

                        e = new VarExp(loc, this);
                        e.type = e.type.mutableOf().unSharedOf(); // Hack for mutable ctor on immutable instances
                        e = new DotVarExp(loc, e, cd.dtor, false);
                        e = new CallExp(loc, e);
                        break;
                    }

                    // delete this;
                    Expression ec;
                    ec = new VarExp(loc, this);
                    e = new DeleteExp(loc, ec, true);
                    e.type = Type.tvoid;
                    break;
                }
            }
        }
        return e;
    }

    /*******************************************
     * If variable has a constant expression initializer, get it.
     * Otherwise, return null.
     */
    extern (D) final Expression getConstInitializer(bool needFullType = true)
    {
        assert(type && _init);

        // Ungag errors when not speculative
        uint oldgag = global.gag;
        if (global.gag)
        {
            Dsymbol sym = toParent().isAggregateDeclaration();
            if (sym && !sym.isSpeculative())
                global.gag = 0;
        }

        if (_scope)
        {
            inuse++;
            _init = _init.initializerSemantic(_scope, type, INITinterpret);
            _scope = null;
            inuse--;
        }

        Expression e = _init.initializerToExpression(needFullType ? type : null);
        global.gag = oldgag;
        return e;
    }

    /*******************************************
     * Helper function for the expansion of manifest constant.
     */
    extern (D) final Expression expandInitializer(Loc loc)
    {
        assert((storage_class & STC.manifest) && _init);

        auto e = getConstInitializer();
        if (!e)
        {
            .error(loc, "cannot make expression out of initializer for `%s`", toChars());
            return ErrorExp.get();
        }

        e = e.copy();
        e.loc = loc;    // for better error message
        return e;
    }

    override final void checkCtorConstInit()
    {
        version (none)
        {
            /* doesn't work if more than one static ctor */
            if (ctorinit == 0 && isCtorinit() && !isField())
                error("missing initializer in static constructor for const variable");
        }
    }

    /************************************
     * Check to see if this variable is actually in an enclosing function
     * rather than the current one.
     * Update nestedrefs[], closureVars[] and outerVars[].
     * Returns: true if error occurs.
     */
    extern (D) final bool checkNestedReference(Scope* sc, Loc loc)
    {
        //printf("VarDeclaration::checkNestedReference() %s\n", toChars());
        if (sc.intypeof == 1 || (sc.flags & SCOPE.ctfe))
            return false;
        if (!parent || parent == sc.parent)
            return false;
        if (isDataseg() || (storage_class & STC.manifest))
            return false;

        // The current function
        FuncDeclaration fdthis = sc.parent.isFuncDeclaration();
        if (!fdthis)
            return false; // out of function scope

        Dsymbol p = toParent2();

        // Function literals from fdthis to p must be delegates
        ensureStaticLinkTo(fdthis, p);

        // The function that this variable is in
        FuncDeclaration fdv = p.isFuncDeclaration();
        if (!fdv || fdv == fdthis)
            return false;

        // Add fdthis to nestedrefs[] if not already there
        if (!nestedrefs.contains(fdthis))
            nestedrefs.push(fdthis);

        //printf("\tfdv = %s\n", fdv.toChars());
        //printf("\tfdthis = %s\n", fdthis.toChars());
        if (loc.isValid())
        {
            if (fdthis.getLevelAndCheck(loc, sc, fdv, this) == fdthis.LevelError)
                return true;
        }

        // Add this VarDeclaration to fdv.closureVars[] if not already there
        if (!sc.intypeof && !(sc.flags & SCOPE.compile) &&
            // https://issues.dlang.org/show_bug.cgi?id=17605
            (fdv.flags & FUNCFLAG.compileTimeOnly || !(fdthis.flags & FUNCFLAG.compileTimeOnly))
           )
        {
            if (!fdv.closureVars.contains(this))
                fdv.closureVars.push(this);
        }

        if (!fdthis.outerVars.contains(this))
            fdthis.outerVars.push(this);

        //printf("fdthis is %s\n", fdthis.toChars());
        //printf("var %s in function %s is nested ref\n", toChars(), fdv.toChars());
        // __dollar creates problems because it isn't a real variable
        // https://issues.dlang.org/show_bug.cgi?id=3326
        if (ident == Id.dollar)
        {
            .error(loc, "cannnot use `$` inside a function literal");
            return true;
        }
        if (ident == Id.withSym) // https://issues.dlang.org/show_bug.cgi?id=1759
        {
            ExpInitializer ez = _init.isExpInitializer();
            assert(ez);
            Expression e = ez.exp;
            if (e.op == EXP.construct || e.op == EXP.blit)
                e = (cast(AssignExp)e).e2;
            return lambdaCheckForNestedRef(e, sc);
        }

        return false;
    }

    override final Dsymbol toAlias()
    {
        //printf("VarDeclaration::toAlias('%s', this = %p, aliassym = %p)\n", toChars(), this, aliassym);
        if ((!type || !type.deco) && _scope)
            dsymbolSemantic(this, _scope);

        assert(this != aliassym);
        Dsymbol s = aliassym ? aliassym.toAlias() : this;
        return s;
    }

    // Eliminate need for dynamic_cast
    override final inout(VarDeclaration) isVarDeclaration() inout
    {
        return this;
    }

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

/*******************************************************
 * C11 6.7.2.1-4 bit fields
 */
extern (C++) class BitFieldDeclaration : VarDeclaration
{
    Expression width;

    uint fieldWidth;
    uint bitOffset;

    final extern (D) this(const ref Loc loc, Type type, Identifier ident, Expression width)
    {
        super(loc, type, ident, null);

        this.width = width;
        this.storage_class |= STC.field;
    }

    override BitFieldDeclaration syntaxCopy(Dsymbol s)
    {
        //printf("BitFieldDeclaration::syntaxCopy(%s)\n", toChars());
        assert(!s);
        auto bf = new BitFieldDeclaration(loc, type ? type.syntaxCopy() : null, ident, width.syntaxCopy());
        bf.comment = comment;
        return bf;
    }

    override final inout(BitFieldDeclaration) isBitFieldDeclaration() inout
    {
        return this;
    }

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

    override final void setFieldOffset(AggregateDeclaration ad, ref FieldState fieldState, bool isunion)
    {
        //printf("BitFieldDeclaration::setFieldOffset(ad: %s, field: %s)\n", ad.toChars(), toChars());
        static void print(const ref FieldState fieldState)
        {
            printf("FieldState.offset      = %d bytes\n",   fieldState.offset);
            printf("          .fieldOffset = %d bytes\n",   fieldState.fieldOffset);
            printf("          .bitOffset   = %d bits\n",    fieldState.bitOffset);
            printf("          .fieldSize   = %d bytes\n",   fieldState.fieldSize);
            printf("          .inFlight    = %d\n\n", fieldState.inFlight);
        }
        //print(fieldState);

        Type t = type.toBasetype();
        const bool anon = isAnonymous();

        // List in ad.fields. Even if the type is error, it's necessary to avoid
        // pointless error diagnostic "more initializers than fields" on struct literal.
        if (!anon)
            ad.fields.push(this);

        if (t.ty == Terror)
            return;

        const sz = t.size(loc);
        assert(sz != SIZE_INVALID && sz < uint.max);
        uint memsize = cast(uint)sz;                // size of member
        uint memalignsize = target.fieldalign(t);   // size of member for alignment purposes

        if (fieldWidth == 0 && !anon)
            error(loc, "named bit fields cannot have 0 width");
        if (fieldWidth > memsize * 8)
            error(loc, "bit field width %d is larger than type", fieldWidth);

        const style = target.c.bitFieldStyle;

        void startNewField()
        {
            uint alignsize;
            if (style == TargetC.BitFieldStyle.Gcc_Clang)
            {
                if (fieldWidth > 32)
                    alignsize = memalignsize;
                else if (fieldWidth > 16)
                    alignsize = 4;
                else if (fieldWidth > 8)
                    alignsize = 2;
                else
                    alignsize = 1;
            }
            else
                alignsize = memsize; // not memalignsize

            uint dummy;
            offset = AggregateDeclaration.placeField(
                &fieldState.offset,
                memsize, alignsize, alignment,
                &ad.structsize,
                (anon && style == TargetC.BitFieldStyle.Gcc_Clang) ? &dummy : &ad.alignsize,
                isunion);

            fieldState.inFlight = true;
            fieldState.fieldOffset = offset;
            fieldState.bitOffset = 0;
            fieldState.fieldSize = memsize;
        }

        if (style == TargetC.BitFieldStyle.Gcc_Clang)
        {
            if (fieldWidth == 0)
            {
                if (!isunion)
                {
                    // Use type of zero width field to align to next field
                    fieldState.offset = (fieldState.offset + memalignsize - 1) & ~(memalignsize - 1);
                    ad.structsize = fieldState.offset;
                }

                fieldState.inFlight = false;
                return;
            }

            if (ad.alignsize == 0)
                ad.alignsize = 1;
            if (!anon &&
                  ad.alignsize < memalignsize)
                ad.alignsize = memalignsize;
        }
        else if (style == TargetC.BitFieldStyle.MS)
        {
            if (ad.alignsize == 0)
                ad.alignsize = 1;
            if (fieldWidth == 0)
            {
                if (fieldState.inFlight && !isunion)
                {
                    // documentation says align to next int
                    //const alsz = cast(uint)Type.tint32.size();
                    const alsz = memsize; // but it really does this
                    fieldState.offset = (fieldState.offset + alsz - 1) & ~(alsz - 1);
                    ad.structsize = fieldState.offset;
                }

                fieldState.inFlight = false;
                return;
            }
        }
        else if (style == TargetC.BitFieldStyle.DM)
        {
            if (anon && fieldWidth && (!fieldState.inFlight || fieldState.bitOffset == 0))
                return;  // this probably should be a bug in DMC
            if (ad.alignsize == 0)
                ad.alignsize = 1;
            if (fieldWidth == 0)
            {
                if (fieldState.inFlight && !isunion)
                {
                    const alsz = memsize;
                    fieldState.offset = (fieldState.offset + alsz - 1) & ~(alsz - 1);
                    ad.structsize = fieldState.offset;
                }

                fieldState.inFlight = false;
                return;
            }
        }

        if (!fieldState.inFlight)
        {
            startNewField();
        }
        else if (style == TargetC.BitFieldStyle.Gcc_Clang)
        {
            if (fieldState.bitOffset + fieldWidth > memsize * 8)
            {
                //printf("start1 fieldState.bitOffset:%u fieldWidth:%u memsize:%u\n", fieldState.bitOffset, fieldWidth, memsize);
                startNewField();
            }
            else
            {
                // if alignment boundary is crossed
                uint start = fieldState.fieldOffset * 8 + fieldState.bitOffset;
                uint end   = start + fieldWidth;
                //printf("%s start: %d end: %d memalignsize: %d\n", ad.toChars(), start, end, memalignsize);
                if (start / (memalignsize * 8) != (end - 1) / (memalignsize * 8))
                {
                    //printf("alignment is crossed\n");
                    startNewField();
                }
            }
        }
        else if (style == TargetC.BitFieldStyle.DM ||
                 style == TargetC.BitFieldStyle.MS)
        {
            if (memsize != fieldState.fieldSize ||
                fieldState.bitOffset + fieldWidth > fieldState.fieldSize * 8)
            {
                startNewField();
            }
        }
        else
            assert(0);

        offset = fieldState.fieldOffset;
        bitOffset = fieldState.bitOffset;

        const pastField = bitOffset + fieldWidth;
        if (style == TargetC.BitFieldStyle.Gcc_Clang)
        {
            auto size = (pastField + 7) / 8;
            fieldState.fieldSize = size;
            //printf(" offset: %d, size: %d\n", offset, size);
            ad.structsize = offset + size;
        }
        else
            fieldState.fieldSize = memsize;
        //printf("at end: ad.structsize = %d\n", cast(int)ad.structsize);
        //print(fieldState);

        if (!isunion)
        {
            fieldState.offset = offset + fieldState.fieldSize;
            fieldState.bitOffset = pastField;
        }

        //printf("\t%s: memalignsize = %d\n", toChars(), memalignsize);
        //printf(" addField '%s' to '%s' at offset %d, size = %d\n", toChars(), ad.toChars(), offset, memsize);
    }
}

/***********************************************************
 * This is a shell around a back end symbol
 */
extern (C++) final class SymbolDeclaration : Declaration
{
    AggregateDeclaration dsym;

    extern (D) this(const ref Loc loc, AggregateDeclaration dsym)
    {
        super(loc, dsym.ident);
        this.dsym = dsym;
        storage_class |= STC.const_;
    }

    // Eliminate need for dynamic_cast
    override inout(SymbolDeclaration) isSymbolDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) class TypeInfoDeclaration : VarDeclaration
{
    Type tinfo;

    final extern (D) this(Type tinfo)
    {
        super(Loc.initial, Type.dtypeinfo.type, tinfo.getTypeInfoIdent(), null);
        this.tinfo = tinfo;
        storage_class = STC.static_ | STC.gshared;
        visibility = Visibility(Visibility.Kind.public_);
        _linkage = LINK.c;
        alignment.set(target.ptrsize);
    }

    static TypeInfoDeclaration create(Type tinfo)
    {
        return new TypeInfoDeclaration(tinfo);
    }

    override final TypeInfoDeclaration syntaxCopy(Dsymbol s)
    {
        assert(0); // should never be produced by syntax
    }

    override final const(char)* toChars() const
    {
        //printf("TypeInfoDeclaration::toChars() tinfo = %s\n", tinfo.toChars());
        OutBuffer buf;
        buf.writestring("typeid(");
        buf.writestring(tinfo.toChars());
        buf.writeByte(')');
        return buf.extractChars();
    }

    override final inout(TypeInfoDeclaration) isTypeInfoDeclaration() inout @nogc nothrow pure @safe
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoStructDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfostruct)
        {
            ObjectNotFound(Id.TypeInfo_Struct);
        }
        type = Type.typeinfostruct.type;
    }

    static TypeInfoStructDeclaration create(Type tinfo)
    {
        return new TypeInfoStructDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoClassDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfoclass)
        {
            ObjectNotFound(Id.TypeInfo_Class);
        }
        type = Type.typeinfoclass.type;
    }

    static TypeInfoClassDeclaration create(Type tinfo)
    {
        return new TypeInfoClassDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoInterfaceDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfointerface)
        {
            ObjectNotFound(Id.TypeInfo_Interface);
        }
        type = Type.typeinfointerface.type;
    }

    static TypeInfoInterfaceDeclaration create(Type tinfo)
    {
        return new TypeInfoInterfaceDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoPointerDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfopointer)
        {
            ObjectNotFound(Id.TypeInfo_Pointer);
        }
        type = Type.typeinfopointer.type;
    }

    static TypeInfoPointerDeclaration create(Type tinfo)
    {
        return new TypeInfoPointerDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoArrayDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfoarray)
        {
            ObjectNotFound(Id.TypeInfo_Array);
        }
        type = Type.typeinfoarray.type;
    }

    static TypeInfoArrayDeclaration create(Type tinfo)
    {
        return new TypeInfoArrayDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoStaticArrayDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfostaticarray)
        {
            ObjectNotFound(Id.TypeInfo_StaticArray);
        }
        type = Type.typeinfostaticarray.type;
    }

    static TypeInfoStaticArrayDeclaration create(Type tinfo)
    {
        return new TypeInfoStaticArrayDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoAssociativeArrayDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfoassociativearray)
        {
            ObjectNotFound(Id.TypeInfo_AssociativeArray);
        }
        type = Type.typeinfoassociativearray.type;
    }

    static TypeInfoAssociativeArrayDeclaration create(Type tinfo)
    {
        return new TypeInfoAssociativeArrayDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoEnumDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfoenum)
        {
            ObjectNotFound(Id.TypeInfo_Enum);
        }
        type = Type.typeinfoenum.type;
    }

    static TypeInfoEnumDeclaration create(Type tinfo)
    {
        return new TypeInfoEnumDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoFunctionDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfofunction)
        {
            ObjectNotFound(Id.TypeInfo_Function);
        }
        type = Type.typeinfofunction.type;
    }

    static TypeInfoFunctionDeclaration create(Type tinfo)
    {
        return new TypeInfoFunctionDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoDelegateDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfodelegate)
        {
            ObjectNotFound(Id.TypeInfo_Delegate);
        }
        type = Type.typeinfodelegate.type;
    }

    static TypeInfoDelegateDeclaration create(Type tinfo)
    {
        return new TypeInfoDelegateDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoTupleDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfotypelist)
        {
            ObjectNotFound(Id.TypeInfo_Tuple);
        }
        type = Type.typeinfotypelist.type;
    }

    static TypeInfoTupleDeclaration create(Type tinfo)
    {
        return new TypeInfoTupleDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoConstDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfoconst)
        {
            ObjectNotFound(Id.TypeInfo_Const);
        }
        type = Type.typeinfoconst.type;
    }

    static TypeInfoConstDeclaration create(Type tinfo)
    {
        return new TypeInfoConstDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoInvariantDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfoinvariant)
        {
            ObjectNotFound(Id.TypeInfo_Invariant);
        }
        type = Type.typeinfoinvariant.type;
    }

    static TypeInfoInvariantDeclaration create(Type tinfo)
    {
        return new TypeInfoInvariantDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoSharedDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfoshared)
        {
            ObjectNotFound(Id.TypeInfo_Shared);
        }
        type = Type.typeinfoshared.type;
    }

    static TypeInfoSharedDeclaration create(Type tinfo)
    {
        return new TypeInfoSharedDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoWildDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfowild)
        {
            ObjectNotFound(Id.TypeInfo_Wild);
        }
        type = Type.typeinfowild.type;
    }

    static TypeInfoWildDeclaration create(Type tinfo)
    {
        return new TypeInfoWildDeclaration(tinfo);
    }

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

/***********************************************************
 */
extern (C++) final class TypeInfoVectorDeclaration : TypeInfoDeclaration
{
    extern (D) this(Type tinfo)
    {
        super(tinfo);
        if (!Type.typeinfovector)
        {
            ObjectNotFound(Id.TypeInfo_Vector);
        }
        type = Type.typeinfovector.type;
    }

    static TypeInfoVectorDeclaration create(Type tinfo)
    {
        return new TypeInfoVectorDeclaration(tinfo);
    }

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

/***********************************************************
 * For the "this" parameter to member functions
 */
extern (C++) final class ThisDeclaration : VarDeclaration
{
    extern (D) this(const ref Loc loc, Type t)
    {
        super(loc, t, Id.This, null);
        storage_class |= STC.nodtor;
    }

    override ThisDeclaration syntaxCopy(Dsymbol s)
    {
        assert(0); // should never be produced by syntax
    }

    override inout(ThisDeclaration) isThisDeclaration() inout
    {
        return this;
    }

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