d: Merge upstream dmd 3982604c5, druntime bc58b1e9, phobos 12329adb6.

[official-gcc.git] / gcc / d / dmd / func.d

/**
 * Defines a function declaration.
 *
 * Includes:
 * - function/delegate literals
 * - function aliases
 * - (static/shared) constructors/destructors/post-blits
 * - `invariant`
 * - `unittest`
 *
 * Copyright:   Copyright (C) 1999-2021 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/func.d, _func.d)
 * Documentation:  https://dlang.org/phobos/dmd_func.html
 * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/dmd/func.d
 */

module dmd.func;

import core.stdc.stdio;
import core.stdc.string;
import dmd.aggregate;
import dmd.arraytypes;
import dmd.astenums;
import dmd.blockexit;
import dmd.gluelayer;
import dmd.dclass;
import dmd.declaration;
import dmd.delegatize;
import dmd.dinterpret;
import dmd.dmodule;
import dmd.dscope;
import dmd.dstruct;
import dmd.dsymbol;
import dmd.dsymbolsem;
import dmd.dtemplate;
import dmd.errors;
import dmd.escape;
import dmd.expression;
import dmd.globals;
import dmd.hdrgen;
import dmd.id;
import dmd.identifier;
import dmd.init;
import dmd.mtype;
import dmd.objc;
import dmd.root.aav;
import dmd.common.outbuffer;
import dmd.root.rootobject;
import dmd.root.string;
import dmd.root.stringtable;
import dmd.semantic2;
import dmd.semantic3;
import dmd.statement_rewrite_walker;
import dmd.statement;
import dmd.statementsem;
import dmd.tokens;
import dmd.visitor;

/// Inline Status
enum ILS : ubyte
{
    uninitialized,       /// not computed yet
    no,                  /// cannot inline
    yes,                 /// can inline
}

enum BUILTIN : ubyte
{
    unknown = 255,   /// not known if this is a builtin
    unimp = 0,       /// this is not a builtin
    gcc,             /// this is a GCC builtin
    llvm,            /// this is an LLVM builtin
    sin,
    cos,
    tan,
    sqrt,
    fabs,
    ldexp,
    log,
    log2,
    log10,
    exp,
    expm1,
    exp2,
    round,
    floor,
    ceil,
    trunc,
    copysign,
    pow,
    fmin,
    fmax,
    fma,
    isnan,
    isinfinity,
    isfinite,
    bsf,
    bsr,
    bswap,
    popcnt,
    yl2x,
    yl2xp1,
    toPrecFloat,
    toPrecDouble,
    toPrecReal
}

/* Tweak all return statements and dtor call for nrvo_var, for correct NRVO.
 */
extern (C++) final class NrvoWalker : StatementRewriteWalker
{
    alias visit = typeof(super).visit;
public:
    FuncDeclaration fd;
    Scope* sc;

    override void visit(ReturnStatement s)
    {
        // See if all returns are instead to be replaced with a goto returnLabel;
        if (fd.returnLabel)
        {
            /* Rewrite:
             *  return exp;
             * as:
             *  vresult = exp; goto Lresult;
             */
            auto gs = new GotoStatement(s.loc, Id.returnLabel);
            gs.label = fd.returnLabel;

            Statement s1 = gs;
            if (s.exp)
                s1 = new CompoundStatement(s.loc, new ExpStatement(s.loc, s.exp), gs);

            replaceCurrent(s1);
        }
    }

    override void visit(TryFinallyStatement s)
    {
        DtorExpStatement des;
        if (fd.nrvo_can && s.finalbody && (des = s.finalbody.isDtorExpStatement()) !is null &&
            fd.nrvo_var == des.var)
        {
            if (!(global.params.useExceptions && ClassDeclaration.throwable))
            {
                /* Don't need to call destructor at all, since it is nrvo
                 */
                replaceCurrent(s._body);
                s._body.accept(this);
                return;
            }

            /* Normally local variable dtors are called regardless exceptions.
             * But for nrvo_var, its dtor should be called only when exception is thrown.
             *
             * Rewrite:
             *      try { s.body; } finally { nrvo_var.edtor; }
             *      // equivalent with:
             *      //    s.body; scope(exit) nrvo_var.edtor;
             * as:
             *      try { s.body; } catch(Throwable __o) { nrvo_var.edtor; throw __o; }
             *      // equivalent with:
             *      //    s.body; scope(failure) nrvo_var.edtor;
             */
            Statement sexception = new DtorExpStatement(Loc.initial, fd.nrvo_var.edtor, fd.nrvo_var);
            Identifier id = Identifier.generateId("__o");

            Statement handler = new PeelStatement(sexception);
            if (sexception.blockExit(fd, false) & BE.fallthru)
            {
                auto ts = new ThrowStatement(Loc.initial, new IdentifierExp(Loc.initial, id));
                ts.internalThrow = true;
                handler = new CompoundStatement(Loc.initial, handler, ts);
            }

            auto catches = new Catches();
            auto ctch = new Catch(Loc.initial, getThrowable(), id, handler);
            ctch.internalCatch = true;
            ctch.catchSemantic(sc); // Run semantic to resolve identifier '__o'
            catches.push(ctch);

            Statement s2 = new TryCatchStatement(Loc.initial, s._body, catches);
            fd.eh_none = false;
            replaceCurrent(s2);
            s2.accept(this);
        }
        else
            StatementRewriteWalker.visit(s);
    }
}

enum FUNCFLAG : uint
{
    purityInprocess  = 1,      /// working on determining purity
    safetyInprocess  = 2,      /// working on determining safety
    nothrowInprocess = 4,      /// working on determining nothrow
    nogcInprocess    = 8,      /// working on determining @nogc
    returnInprocess  = 0x10,   /// working on inferring 'return' for parameters
    inlineScanned    = 0x20,   /// function has been scanned for inline possibilities
    inferScope       = 0x40,   /// infer 'scope' for parameters
    hasCatches       = 0x80,   /// function has try-catch statements
    compileTimeOnly  = 0x100,  /// is a compile time only function; no code will be generated for it
    printf           = 0x200,  /// is a printf-like function
    scanf            = 0x400,  /// is a scanf-like function
    noreturn         = 0x800,  /// the function does not return
}

/***********************************************************
 * Tuple of result identifier (possibly null) and statement.
 * This is used to store out contracts: out(id){ ensure }
 */
extern (C++) struct Ensure
{
    Identifier id;
    Statement ensure;

    Ensure syntaxCopy()
    {
        return Ensure(id, ensure.syntaxCopy());
    }

    /*****************************************
     * Do syntax copy of an array of Ensure's.
     */
    static Ensures* arraySyntaxCopy(Ensures* a)
    {
        Ensures* b = null;
        if (a)
        {
            b = a.copy();
            foreach (i, e; *a)
            {
                (*b)[i] = e.syntaxCopy();
            }
        }
        return b;
    }

}

/***********************************************************
 */
extern (C++) class FuncDeclaration : Declaration
{
    Statements* frequires;              /// in contracts
    Ensures* fensures;                  /// out contracts
    Statement frequire;                 /// lowered in contract
    Statement fensure;                  /// lowered out contract
    Statement fbody;                    /// function body

    FuncDeclarations foverrides;        /// functions this function overrides
    FuncDeclaration fdrequire;          /// function that does the in contract
    FuncDeclaration fdensure;           /// function that does the out contract

    Expressions* fdrequireParams;       /// argument list for __require
    Expressions* fdensureParams;        /// argument list for __ensure

    const(char)* mangleString;          /// mangled symbol created from mangleExact()

    VarDeclaration vresult;             /// result variable for out contracts
    LabelDsymbol returnLabel;           /// where the return goes

    bool[size_t] isTypeIsolatedCache;   /// cache for the potentially very expensive isTypeIsolated check

    // used to prevent symbols in different
    // scopes from having the same name
    DsymbolTable localsymtab;
    VarDeclaration vthis;               /// 'this' parameter (member and nested)
    bool isThis2;                       /// has a dual-context 'this' parameter
    VarDeclaration v_arguments;         /// '_arguments' parameter

    VarDeclaration v_argptr;            /// '_argptr' variable
    VarDeclarations* parameters;        /// Array of VarDeclaration's for parameters
    DsymbolTable labtab;                /// statement label symbol table
    Dsymbol overnext;                   /// next in overload list
    FuncDeclaration overnext0;          /// next in overload list (only used during IFTI)
    Loc endloc;                         /// location of closing curly bracket
    int vtblIndex = -1;                 /// for member functions, index into vtbl[]
    bool naked;                         /// true if naked
    bool generated;                     /// true if function was generated by the compiler rather than
                                        /// supplied by the user
    bool hasAlwaysInlines;              /// contains references to functions that must be inlined
    ubyte isCrtCtorDtor;                /// has attribute pragma(crt_constructor(1)/crt_destructor(2))
                                        /// not set before the glue layer

    ILS inlineStatusStmt = ILS.uninitialized;
    ILS inlineStatusExp = ILS.uninitialized;
    PINLINE inlining = PINLINE.default_;

    int inlineNest;                     /// !=0 if nested inline
    bool eh_none;                       /// true if no exception unwinding is needed

    bool semantic3Errors;               /// true if errors in semantic3 this function's frame ptr
    ForeachStatement fes;               /// if foreach body, this is the foreach
    BaseClass* interfaceVirtual;        /// if virtual, but only appears in base interface vtbl[]
    bool introducing;                   /// true if 'introducing' function
    /** if !=NULL, then this is the type
    of the 'introducing' function
    this one is overriding
    */
    Type tintro;

    bool inferRetType;                  /// true if return type is to be inferred
    StorageClass storage_class2;        /// storage class for template onemember's

    // Things that should really go into Scope

    /// 1 if there's a return exp; statement
    /// 2 if there's a throw statement
    /// 4 if there's an assert(0)
    /// 8 if there's inline asm
    /// 16 if there are multiple return statements
    int hasReturnExp;

    // Support for NRVO (named return value optimization)
    bool nrvo_can = true;               /// true means we can do NRVO
    VarDeclaration nrvo_var;            /// variable to replace with shidden
    Symbol* shidden;                    /// hidden pointer passed to function

    ReturnStatements* returns;

    GotoStatements* gotos;              /// Gotos with forward references

    /// set if this is a known, builtin function we can evaluate at compile time
    BUILTIN builtin = BUILTIN.unknown;

    /// set if someone took the address of this function
    int tookAddressOf;

    bool requiresClosure;               // this function needs a closure

    /** local variables in this function which are referenced by nested functions
     * (They'll get put into the "closure" for this function.)
     */
    VarDeclarations closureVars;

    /** Outer variables which are referenced by this nested function
     * (the inverse of closureVars)
     */
    VarDeclarations outerVars;

    /// Sibling nested functions which called this one
    FuncDeclarations siblingCallers;

    FuncDeclarations *inlinedNestedCallees;

    uint flags;                        /// FUNCFLAG.xxxxx

    /**
     * Data for a function declaration that is needed for the Objective-C
     * integration.
     */
    ObjcFuncDeclaration objc;

    extern (D) this(const ref Loc loc, const ref Loc endloc, Identifier ident, StorageClass storage_class, Type type, bool noreturn = false)
    {
        super(loc, ident);
        //printf("FuncDeclaration(id = '%s', type = %p)\n", id.toChars(), type);
        //printf("storage_class = x%x\n", storage_class);
        this.storage_class = storage_class;
        this.type = type;
        if (type)
        {
            // Normalize storage_class, because function-type related attributes
            // are already set in the 'type' in parsing phase.
            this.storage_class &= ~(STC.TYPECTOR | STC.FUNCATTR);
        }
        this.endloc = endloc;
        if (noreturn)
            this.flags |= FUNCFLAG.noreturn;

        /* The type given for "infer the return type" is a TypeFunction with
         * NULL for the return type.
         */
        inferRetType = (type && type.nextOf() is null);
    }

    static FuncDeclaration create(const ref Loc loc, const ref Loc endloc, Identifier id, StorageClass storage_class, Type type, bool noreturn = false)
    {
        return new FuncDeclaration(loc, endloc, id, storage_class, type, noreturn);
    }

    override FuncDeclaration syntaxCopy(Dsymbol s)
    {
        //printf("FuncDeclaration::syntaxCopy('%s')\n", toChars());
        FuncDeclaration f = s ? cast(FuncDeclaration)s
                              : new FuncDeclaration(loc, endloc, ident, storage_class, type.syntaxCopy(), (flags & FUNCFLAG.noreturn) != 0);
        f.frequires = frequires ? Statement.arraySyntaxCopy(frequires) : null;
        f.fensures = fensures ? Ensure.arraySyntaxCopy(fensures) : null;
        f.fbody = fbody ? fbody.syntaxCopy() : null;
        return f;
    }

    /****************************************************
     * Resolve forward reference of function signature -
     * parameter types, return type, and attributes.
     * Returns:
     *  false if any errors exist in the signature.
     */
    final bool functionSemantic()
    {
        //printf("functionSemantic() %p %s\n", this, toChars());
        if (!_scope)
            return !errors;

        this.cppnamespace = _scope.namespace;

        if (!originalType) // semantic not yet run
        {
            TemplateInstance spec = isSpeculative();
            uint olderrs = global.errors;
            uint oldgag = global.gag;
            if (global.gag && !spec)
                global.gag = 0;
            dsymbolSemantic(this, _scope);
            global.gag = oldgag;
            if (spec && global.errors != olderrs)
                spec.errors = (global.errors - olderrs != 0);
            if (olderrs != global.errors) // if errors compiling this function
                return false;
        }

        // if inferring return type, sematic3 needs to be run
        // - When the function body contains any errors, we cannot assume
        //   the inferred return type is valid.
        //   So, the body errors should become the function signature error.
        if (inferRetType && type && !type.nextOf())
            return functionSemantic3();

        TemplateInstance ti;
        if (isInstantiated() && !isVirtualMethod() &&
            ((ti = parent.isTemplateInstance()) is null || ti.isTemplateMixin() || ti.tempdecl.ident == ident))
        {
            AggregateDeclaration ad = isMemberLocal();
            if (ad && ad.sizeok != Sizeok.done)
            {
                /* Currently dmd cannot resolve forward references per methods,
                 * then setting SIZOKfwd is too conservative and would break existing code.
                 * So, just stop method attributes inference until ad.dsymbolSemantic() done.
                 */
                //ad.sizeok = Sizeok.fwd;
            }
            else
                return functionSemantic3() || !errors;
        }

        if (storage_class & STC.inference)
            return functionSemantic3() || !errors;

        return !errors;
    }

    /****************************************************
     * Resolve forward reference of function body.
     * Returns false if any errors exist in the body.
     */
    final bool functionSemantic3()
    {
        if (semanticRun < PASS.semantic3 && _scope)
        {
            /* Forward reference - we need to run semantic3 on this function.
             * If errors are gagged, and it's not part of a template instance,
             * we need to temporarily ungag errors.
             */
            TemplateInstance spec = isSpeculative();
            uint olderrs = global.errors;
            uint oldgag = global.gag;
            if (global.gag && !spec)
                global.gag = 0;
            semantic3(this, _scope);
            global.gag = oldgag;

            // If it is a speculatively-instantiated template, and errors occur,
            // we need to mark the template as having errors.
            if (spec && global.errors != olderrs)
                spec.errors = (global.errors - olderrs != 0);
            if (olderrs != global.errors) // if errors compiling this function
                return false;
        }

        return !errors && !semantic3Errors;
    }

    /****************************************************
     * Check that this function type is properly resolved.
     * If not, report "forward reference error" and return true.
     */
    extern (D) final bool checkForwardRef(const ref Loc loc)
    {
        if (!functionSemantic())
            return true;

        /* No deco means the functionSemantic() call could not resolve
         * forward referenes in the type of this function.
         */
        if (!type.deco)
        {
            bool inSemantic3 = (inferRetType && semanticRun >= PASS.semantic3);
            .error(loc, "forward reference to %s`%s`",
                (inSemantic3 ? "inferred return type of function " : "").ptr,
                toChars());
            return true;
        }
        return false;
    }

    // called from semantic3
    /**
     * Creates and returns the hidden parameters for this function declaration.
     *
     * Hidden parameters include the `this` parameter of a class, struct or
     * nested function and the selector parameter for Objective-C methods.
     */
    extern (D) final void declareThis(Scope* sc)
    {
        isThis2 = toParent2() != toParentLocal();
        auto ad = isThis();
        if (!isThis2 && !ad && !isNested())
        {
            vthis = null;
            objc.selectorParameter = null;
            return;
        }

        Type addModStc(Type t)
        {
            return t.addMod(type.mod).addStorageClass(storage_class);
        }

        if (isThis2 || isNested())
        {
            /* The 'this' for a nested function is the link to the
             * enclosing function's stack frame.
             * Note that nested functions and member functions are disjoint.
             */
            Type tthis = addModStc(isThis2 ?
                                   Type.tvoidptr.sarrayOf(2).pointerTo() :
                                   Type.tvoid.pointerTo());
            vthis = new VarDeclaration(loc, tthis, isThis2 ? Id.this2 : Id.capture, null);
            vthis.storage_class |= STC.parameter | STC.nodtor;
        }
        else if (ad)
        {
            Type thandle = addModStc(ad.handleType());
            vthis = new ThisDeclaration(loc, thandle);
            vthis.storage_class |= STC.parameter;
            if (thandle.ty == Tstruct)
            {
                vthis.storage_class |= STC.ref_;
                // if member function is marked 'inout', then 'this' is 'return ref'
                if (type.ty == Tfunction && (cast(TypeFunction)type).isInOutQual())
                    vthis.storage_class |= STC.return_;
            }
        }

        if (auto tf = type.isTypeFunction())
        {
            if (tf.isreturn)
                vthis.storage_class |= STC.return_;
            if (tf.isScopeQual)
                vthis.storage_class |= STC.scope_;

            /* Add STC.returnScope like typesem.d does for TypeFunction parameters,
             * at least it should be the same. At the moment, we'll just
             * do existing practice. But we should examine how TypeFunction does
             * it, for consistency.
             */
            if (!tf.isref && isRefReturnScope(vthis.storage_class))
            {
                /* if `ref return scope`, evaluate to `ref` `return scope`
                 */
                vthis.storage_class |= STC.returnScope;
            }
        }
        if (flags & FUNCFLAG.inferScope && !(vthis.storage_class & STC.scope_))
            vthis.storage_class |= STC.maybescope;

        vthis.dsymbolSemantic(sc);
        if (!sc.insert(vthis))
            assert(0);
        vthis.parent = this;
        if (ad)
            objc.selectorParameter = .objc.createSelectorParameter(this, sc);
    }

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

        if (auto s = isDsymbol(o))
        {
            auto fd1 = this;
            auto fd2 = s.isFuncDeclaration();
            if (!fd2)
                return false;

            auto fa1 = fd1.isFuncAliasDeclaration();
            auto faf1 = fa1 ? fa1.toAliasFunc() : fd1;

            auto fa2 = fd2.isFuncAliasDeclaration();
            auto faf2 = fa2 ? fa2.toAliasFunc() : fd2;

            if (fa1 && fa2)
            {
                return faf1.equals(faf2) && fa1.hasOverloads == fa2.hasOverloads;
            }

            bool b1 = fa1 !is null;
            if (b1 && faf1.isUnique() && !fa1.hasOverloads)
                b1 = false;

            bool b2 = fa2 !is null;
            if (b2 && faf2.isUnique() && !fa2.hasOverloads)
                b2 = false;

            if (b1 != b2)
                return false;

            return faf1.toParent().equals(faf2.toParent()) &&
                   faf1.ident.equals(faf2.ident) &&
                   faf1.type.equals(faf2.type);
        }
        return false;
    }

    /****************************************************
     * Determine if 'this' overrides fd.
     * Return !=0 if it does.
     */
    final int overrides(FuncDeclaration fd)
    {
        int result = 0;
        if (fd.ident == ident)
        {
            const cov = type.covariant(fd.type);
            if (cov != Covariant.distinct)
            {
                ClassDeclaration cd1 = toParent().isClassDeclaration();
                ClassDeclaration cd2 = fd.toParent().isClassDeclaration();
                if (cd1 && cd2 && cd2.isBaseOf(cd1, null))
                    result = 1;
            }
        }
        return result;
    }

    /*************************************************
     * Find index of function in vtbl[0..dim] that
     * this function overrides.
     * Prefer an exact match to a covariant one.
     * Params:
     *      vtbl     = vtable to use
     *      dim      = maximal vtable dimension
     * Returns:
     *      -1      didn't find one
     *      -2      can't determine because of forward references
     */
    final int findVtblIndex(Dsymbols* vtbl, int dim)
    {
        //printf("findVtblIndex() %s\n", toChars());
        FuncDeclaration mismatch = null;
        StorageClass mismatchstc = 0;
        int mismatchvi = -1;
        int exactvi = -1;
        int bestvi = -1;
        for (int vi = 0; vi < dim; vi++)
        {
            FuncDeclaration fdv = (*vtbl)[vi].isFuncDeclaration();
            if (fdv && fdv.ident == ident)
            {
                if (type.equals(fdv.type)) // if exact match
                {
                    if (fdv.parent.isClassDeclaration())
                    {
                        if (fdv.isFuture())
                        {
                            bestvi = vi;
                            continue;           // keep looking
                        }
                        return vi; // no need to look further
                    }

                    if (exactvi >= 0)
                    {
                        error("cannot determine overridden function");
                        return exactvi;
                    }
                    exactvi = vi;
                    bestvi = vi;
                    continue;
                }

                StorageClass stc = 0;
                const cov = type.covariant(fdv.type, &stc);
                //printf("\tbaseclass cov = %d\n", cov);
                final switch (cov)
                {
                case Covariant.distinct:
                    // types are distinct
                    break;

                case Covariant.yes:
                    bestvi = vi; // covariant, but not identical
                    break;
                    // keep looking for an exact match

                case Covariant.no:
                    mismatchvi = vi;
                    mismatchstc = stc;
                    mismatch = fdv; // overrides, but is not covariant
                    break;
                    // keep looking for an exact match

                case Covariant.fwdref:
                    return -2; // forward references
                }
            }
        }
        if (bestvi == -1 && mismatch)
        {
            //type.print();
            //mismatch.type.print();
            //printf("%s %s\n", type.deco, mismatch.type.deco);
            //printf("stc = %llx\n", mismatchstc);
            if (mismatchstc)
            {
                // Fix it by modifying the type to add the storage classes
                type = type.addStorageClass(mismatchstc);
                bestvi = mismatchvi;
            }
        }
        return bestvi;
    }

    /*********************************
     * If function a function in a base class,
     * return that base class.
     * Returns:
     *  base class if overriding, null if not
     */
    final BaseClass* overrideInterface()
    {
        for (ClassDeclaration cd = toParent2().isClassDeclaration(); cd; cd = cd.baseClass)
        {
            foreach (b; cd.interfaces)
            {
                auto v = findVtblIndex(&b.sym.vtbl, cast(int)b.sym.vtbl.dim);
                if (v >= 0)
                    return b;
            }
        }
        return null;
    }

    /****************************************************
     * Overload this FuncDeclaration with the new one f.
     * Return true if successful; i.e. no conflict.
     */
    override bool overloadInsert(Dsymbol s)
    {
        //printf("FuncDeclaration::overloadInsert(s = %s) this = %s\n", s.toChars(), toChars());
        assert(s != this);
        AliasDeclaration ad = s.isAliasDeclaration();
        if (ad)
        {
            if (overnext)
                return overnext.overloadInsert(ad);
            if (!ad.aliassym && ad.type.ty != Tident && ad.type.ty != Tinstance && ad.type.ty != Ttypeof)
            {
                //printf("\tad = '%s'\n", ad.type.toChars());
                return false;
            }
            overnext = ad;
            //printf("\ttrue: no conflict\n");
            return true;
        }
        TemplateDeclaration td = s.isTemplateDeclaration();
        if (td)
        {
            if (!td.funcroot)
                td.funcroot = this;
            if (overnext)
                return overnext.overloadInsert(td);
            overnext = td;
            return true;
        }
        FuncDeclaration fd = s.isFuncDeclaration();
        if (!fd)
            return false;

        version (none)
        {
            /* Disable this check because:
             *  const void foo();
             * semantic() isn't run yet on foo(), so the const hasn't been
             * applied yet.
             */
            if (type)
            {
                printf("type = %s\n", type.toChars());
                printf("fd.type = %s\n", fd.type.toChars());
            }
            // fd.type can be NULL for overloaded constructors
            if (type && fd.type && fd.type.covariant(type) && fd.type.mod == type.mod && !isFuncAliasDeclaration())
            {
                //printf("\tfalse: conflict %s\n", kind());
                return false;
            }
        }

        if (overnext)
        {
            td = overnext.isTemplateDeclaration();
            if (td)
                fd.overloadInsert(td);
            else
                return overnext.overloadInsert(fd);
        }
        overnext = fd;
        //printf("\ttrue: no conflict\n");
        return true;
    }

    /********************************************
     * Find function in overload list that exactly matches t.
     */
    extern (D) final FuncDeclaration overloadExactMatch(Type t)
    {
        FuncDeclaration fd;
        overloadApply(this, (Dsymbol s)
        {
            auto f = s.isFuncDeclaration();
            if (!f)
                return 0;
            if (t.equals(f.type))
            {
                fd = f;
                return 1;
            }

            /* Allow covariant matches, as long as the return type
             * is just a const conversion.
             * This allows things like pure functions to match with an impure function type.
             */
            if (t.ty == Tfunction)
            {
                auto tf = cast(TypeFunction)f.type;
                if (tf.covariant(t) == Covariant.yes &&
                    tf.nextOf().implicitConvTo(t.nextOf()) >= MATCH.constant)
                {
                    fd = f;
                    return 1;
                }
            }
            return 0;
        });
        return fd;
    }

    /********************************************
     * Find function in overload list that matches to the 'this' modifier.
     * There's four result types.
     *
     * 1. If the 'tthis' matches only one candidate, it's an "exact match".
     *    Returns the function and 'hasOverloads' is set to false.
     *      eg. If 'tthis" is mutable and there's only one mutable method.
     * 2. If there's two or more match candidates, but a candidate function will be
     *    a "better match".
     *    Returns the better match function but 'hasOverloads' is set to true.
     *      eg. If 'tthis' is mutable, and there's both mutable and const methods,
     *          the mutable method will be a better match.
     * 3. If there's two or more match candidates, but there's no better match,
     *    Returns null and 'hasOverloads' is set to true to represent "ambiguous match".
     *      eg. If 'tthis' is mutable, and there's two or more mutable methods.
     * 4. If there's no candidates, it's "no match" and returns null with error report.
     *      e.g. If 'tthis' is const but there's no const methods.
     */
    extern (D) final FuncDeclaration overloadModMatch(const ref Loc loc, Type tthis, ref bool hasOverloads)
    {
        //printf("FuncDeclaration::overloadModMatch('%s')\n", toChars());
        MatchAccumulator m;
        overloadApply(this, (Dsymbol s)
        {
            auto f = s.isFuncDeclaration();
            if (!f || f == m.lastf) // skip duplicates
                return 0;

            auto tf = f.type.toTypeFunction();
            //printf("tf = %s\n", tf.toChars());

            MATCH match;
            if (tthis) // non-static functions are preferred than static ones
            {
                if (f.needThis())
                    match = f.isCtorDeclaration() ? MATCH.exact : MODmethodConv(tthis.mod, tf.mod);
                else
                    match = MATCH.constant; // keep static function in overload candidates
            }
            else // static functions are preferred than non-static ones
            {
                if (f.needThis())
                    match = MATCH.convert;
                else
                    match = MATCH.exact;
            }
            if (match == MATCH.nomatch)
                return 0;

            if (match > m.last) goto LcurrIsBetter;
            if (match < m.last) goto LlastIsBetter;

            // See if one of the matches overrides the other.
            if (m.lastf.overrides(f)) goto LlastIsBetter;
            if (f.overrides(m.lastf)) goto LcurrIsBetter;

            //printf("\tambiguous\n");
            m.nextf = f;
            m.count++;
            return 0;

        LlastIsBetter:
            //printf("\tlastbetter\n");
            m.count++; // count up
            return 0;

        LcurrIsBetter:
            //printf("\tisbetter\n");
            if (m.last <= MATCH.convert)
            {
                // clear last secondary matching
                m.nextf = null;
                m.count = 0;
            }
            m.last = match;
            m.lastf = f;
            m.count++; // count up
            return 0;
        });

        if (m.count == 1)       // exact match
        {
            hasOverloads = false;
        }
        else if (m.count > 1)   // better or ambiguous match
        {
            hasOverloads = true;
        }
        else                    // no match
        {
            hasOverloads = true;
            auto tf = this.type.toTypeFunction();
            assert(tthis);
            assert(!MODimplicitConv(tthis.mod, tf.mod)); // modifier mismatch
            {
                OutBuffer thisBuf, funcBuf;
                MODMatchToBuffer(&thisBuf, tthis.mod, tf.mod);
                MODMatchToBuffer(&funcBuf, tf.mod, tthis.mod);
                .error(loc, "%smethod %s is not callable using a %sobject",
                    funcBuf.peekChars(), this.toPrettyChars(), thisBuf.peekChars());
            }
        }
        return m.lastf;
    }

    /********************************************
     * find function template root in overload list
     */
    extern (D) final TemplateDeclaration findTemplateDeclRoot()
    {
        FuncDeclaration f = this;
        while (f && f.overnext)
        {
            //printf("f.overnext = %p %s\n", f.overnext, f.overnext.toChars());
            TemplateDeclaration td = f.overnext.isTemplateDeclaration();
            if (td)
                return td;
            f = f.overnext.isFuncDeclaration();
        }
        return null;
    }

    /********************************************
     * Returns true if function was declared
     * directly or indirectly in a unittest block
     */
    final bool inUnittest()
    {
        Dsymbol f = this;
        do
        {
            if (f.isUnitTestDeclaration())
                return true;
            f = f.toParent();
        }
        while (f);
        return false;
    }

    /*************************************
     * Determine partial specialization order of 'this' vs g.
     * This is very similar to TemplateDeclaration::leastAsSpecialized().
     * Returns:
     *      match   'this' is at least as specialized as g
     *      0       g is more specialized than 'this'
     */
    final MATCH leastAsSpecialized(FuncDeclaration g)
    {
        enum LOG_LEASTAS = 0;
        static if (LOG_LEASTAS)
        {
            printf("%s.leastAsSpecialized(%s)\n", toChars(), g.toChars());
            printf("%s, %s\n", type.toChars(), g.type.toChars());
        }

        /* This works by calling g() with f()'s parameters, and
         * if that is possible, then f() is at least as specialized
         * as g() is.
         */

        TypeFunction tf = type.toTypeFunction();
        TypeFunction tg = g.type.toTypeFunction();

        /* If both functions have a 'this' pointer, and the mods are not
         * the same and g's is not const, then this is less specialized.
         */
        if (needThis() && g.needThis() && tf.mod != tg.mod)
        {
            if (isCtorDeclaration())
            {
                if (!MODimplicitConv(tg.mod, tf.mod))
                    return MATCH.nomatch;
            }
            else
            {
                if (!MODimplicitConv(tf.mod, tg.mod))
                    return MATCH.nomatch;
            }
        }

        /* Create a dummy array of arguments out of the parameters to f()
         */
        Expressions args;
        foreach (u, p; tf.parameterList)
        {
            Expression e;
            if (p.isReference())
            {
                e = new IdentifierExp(Loc.initial, p.ident);
                e.type = p.type;
            }
            else
                e = p.type.defaultInitLiteral(Loc.initial);
            args.push(e);
        }

        MATCH m = tg.callMatch(null, args[], 1);
        if (m > MATCH.nomatch)
        {
            /* A variadic parameter list is less specialized than a
             * non-variadic one.
             */
            if (tf.parameterList.varargs && !tg.parameterList.varargs)
                goto L1; // less specialized

            static if (LOG_LEASTAS)
            {
                printf("  matches %d, so is least as specialized\n", m);
            }
            return m;
        }
    L1:
        static if (LOG_LEASTAS)
        {
            printf("  doesn't match, so is not as specialized\n");
        }
        return MATCH.nomatch;
    }

    /********************************
     * Searches for a label with the given identifier. This function will insert a new
     * `LabelDsymbol` into `labtab` if it does not contain a mapping for `ident`.
     *
     * Params:
     *   ident = identifier of the requested label
     *   loc   = location used when creating a new `LabelDsymbol`
     *
     * Returns: the `LabelDsymbol` for `ident`
     */
    final LabelDsymbol searchLabel(Identifier ident, const ref Loc loc = Loc.initial)
    {
        Dsymbol s;
        if (!labtab)
            labtab = new DsymbolTable(); // guess we need one

        s = labtab.lookup(ident);
        if (!s)
        {
            s = new LabelDsymbol(ident, loc);
            labtab.insert(s);
        }
        return cast(LabelDsymbol)s;
    }

    /*****************************************
     * Determine lexical level difference from `this` to nested function `fd`.
     * Params:
     *      fd = target of call
     *      intypeof = !=0 if inside typeof
     * Returns:
     *      0       same level
     *      >0      decrease nesting by number
     *      -1      increase nesting by 1 (`fd` is nested within `this`)
     *      LevelError  error, `this` cannot call `fd`
     */
    final int getLevel(FuncDeclaration fd, int intypeof)
    {
        //printf("FuncDeclaration::getLevel(fd = '%s')\n", fd.toChars());
        Dsymbol fdparent = fd.toParent2();
        if (fdparent == this)
            return -1;

        Dsymbol s = this;
        int level = 0;
        while (fd != s && fdparent != s.toParent2())
        {
            //printf("\ts = %s, '%s'\n", s.kind(), s.toChars());
            if (auto thisfd = s.isFuncDeclaration())
            {
                if (!thisfd.isNested() && !thisfd.vthis && !intypeof)
                    return LevelError;
            }
            else
            {
                if (auto thiscd = s.isAggregateDeclaration())
                {
                    /* AggregateDeclaration::isNested returns true only when
                     * it has a hidden pointer.
                     * But, calling the function belongs unrelated lexical scope
                     * is still allowed inside typeof.
                     *
                     * struct Map(alias fun) {
                     *   typeof({ return fun(); }) RetType;
                     *   // No member function makes Map struct 'not nested'.
                     * }
                     */
                    if (!thiscd.isNested() && !intypeof)
                        return LevelError;
                }
                else
                    return LevelError;
            }

            s = s.toParentP(fd);
            assert(s);
            level++;
        }
        return level;
    }

    /***********************************
     * Determine lexical level difference from `this` to nested function `fd`.
     * Issue error if `this` cannot call `fd`.
     *
     * Params:
     *      loc = location for error messages
     *      sc = context
     *      fd = target of call
     *      decl = The `Declaration` that triggered this check.
     *             Used to provide a better error message only.
     * Returns:
     *      0       same level
     *      >0      decrease nesting by number
     *      -1      increase nesting by 1 (`fd` is nested within 'this')
     *      LevelError  error
     */
    final int getLevelAndCheck(const ref Loc loc, Scope* sc, FuncDeclaration fd,
                               Declaration decl)
    {
        int level = getLevel(fd, sc.intypeof);
        if (level != LevelError)
            return level;

        // Don't give error if in template constraint
        if (!(sc.flags & SCOPE.constraint))
        {
            const(char)* xstatic = isStatic() ? "`static` " : "";
            // better diagnostics for static functions
            .error(loc, "%s%s `%s` cannot access %s `%s` in frame of function `%s`",
                   xstatic, kind(), toPrettyChars(), decl.kind(), decl.toChars(),
                   fd.toPrettyChars());
                .errorSupplemental(decl.loc, "`%s` declared here", decl.toChars());
            return LevelError;
        }
        return 1;
    }

    enum LevelError = -2;

    override const(char)* toPrettyChars(bool QualifyTypes = false)
    {
        if (isMain())
            return "D main";
        else
            return Dsymbol.toPrettyChars(QualifyTypes);
    }

    /** for diagnostics, e.g. 'int foo(int x, int y) pure' */
    final const(char)* toFullSignature()
    {
        OutBuffer buf;
        functionToBufferWithIdent(type.toTypeFunction(), &buf, toChars(), isStatic);
        return buf.extractChars();
    }

    final bool isMain() const
    {
        return ident == Id.main && linkage != LINK.c && !isMember() && !isNested();
    }

    final bool isCMain() const
    {
        return ident == Id.main && linkage == LINK.c && !isMember() && !isNested();
    }

    final bool isWinMain() const
    {
        //printf("FuncDeclaration::isWinMain() %s\n", toChars());
        version (none)
        {
            bool x = ident == Id.WinMain && linkage != LINK.c && !isMember();
            printf("%s\n", x ? "yes" : "no");
            return x;
        }
        else
        {
            return ident == Id.WinMain && linkage != LINK.c && !isMember();
        }
    }

    final bool isDllMain() const
    {
        return ident == Id.DllMain && linkage != LINK.c && !isMember();
    }

    final bool isRtInit() const
    {
        return ident == Id.rt_init && linkage == LINK.c && !isMember() && !isNested();
    }

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

    override final bool isImportedSymbol() const
    {
        //printf("isImportedSymbol()\n");
        //printf("protection = %d\n", visibility);
        return (visibility.kind == Visibility.Kind.export_) && !fbody;
    }

    override final bool isCodeseg() const pure nothrow @nogc @safe
    {
        return true; // functions are always in the code segment
    }

    override final bool isOverloadable() const
    {
        return true; // functions can be overloaded
    }

    /***********************************
     * Override so it can work even if semantic() hasn't yet
     * been run.
     */
    override final bool isAbstract()
    {
        if (storage_class & STC.abstract_)
            return true;
        if (semanticRun >= PASS.semanticdone)
            return false;

        if (_scope)
        {
           if (_scope.stc & STC.abstract_)
                return true;
           parent = _scope.parent;
           Dsymbol parent = toParent();
           if (parent.isInterfaceDeclaration())
                return true;
        }
        return false;
    }

    /**********************************
     * Decide if attributes for this function can be inferred from examining
     * the function body.
     * Returns:
     *  true if can
     */
    final bool canInferAttributes(Scope* sc)
    {
        if (!fbody)
            return false;

        if (isVirtualMethod() &&
            /*
             * https://issues.dlang.org/show_bug.cgi?id=21719
             *
             * If we have an auto virtual function we can infer
             * the attributes.
             */
            !(inferRetType && !isCtorDeclaration()))
            return false;               // since they may be overridden

        if (sc.func &&
            /********** this is for backwards compatibility for the moment ********/
            (!isMember() || sc.func.isSafeBypassingInference() && !isInstantiated()))
            return true;

        if (isFuncLiteralDeclaration() ||               // externs are not possible with literals
            (storage_class & STC.inference) ||           // do attribute inference
            (inferRetType && !isCtorDeclaration()))
            return true;

        if (isInstantiated())
        {
            auto ti = parent.isTemplateInstance();
            if (ti is null || ti.isTemplateMixin() || ti.tempdecl.ident == ident)
                return true;
        }

        return false;
    }

    /*****************************************
     * Initialize for inferring the attributes of this function.
     */
    final void initInferAttributes()
    {
        //printf("initInferAttributes() for %s (%s)\n", toPrettyChars(), ident.toChars());
        TypeFunction tf = type.toTypeFunction();
        if (tf.purity == PURE.impure) // purity not specified
            flags |= FUNCFLAG.purityInprocess;

        if (tf.trust == TRUST.default_)
            flags |= FUNCFLAG.safetyInprocess;

        if (!tf.isnothrow)
            flags |= FUNCFLAG.nothrowInprocess;

        if (!tf.isnogc)
            flags |= FUNCFLAG.nogcInprocess;

        if (!isVirtual() || introducing)
            flags |= FUNCFLAG.returnInprocess;

        // Initialize for inferring STC.scope_
        if (global.params.useDIP1000 == FeatureState.enabled)
            flags |= FUNCFLAG.inferScope;
    }

    final PURE isPure()
    {
        //printf("FuncDeclaration::isPure() '%s'\n", toChars());
        TypeFunction tf = type.toTypeFunction();
        if (flags & FUNCFLAG.purityInprocess)
            setImpure();
        if (tf.purity == PURE.fwdref)
            tf.purityLevel();
        PURE purity = tf.purity;
        if (purity > PURE.weak && isNested())
            purity = PURE.weak;
        if (purity > PURE.weak && needThis())
        {
            // The attribute of the 'this' reference affects purity strength
            if (type.mod & MODFlags.immutable_)
            {
            }
            else if (type.mod & (MODFlags.const_ | MODFlags.wild) && purity >= PURE.const_)
                purity = PURE.const_;
            else
                purity = PURE.weak;
        }
        tf.purity = purity;
        // ^ This rely on the current situation that every FuncDeclaration has a
        //   unique TypeFunction.
        return purity;
    }

    final PURE isPureBypassingInference()
    {
        if (flags & FUNCFLAG.purityInprocess)
            return PURE.fwdref;
        else
            return isPure();
    }

    /**************************************
     * The function is doing something impure,
     * so mark it as impure.
     * If there's a purity error, return true.
     */
    extern (D) final bool setImpure()
    {
        if (flags & FUNCFLAG.purityInprocess)
        {
            flags &= ~FUNCFLAG.purityInprocess;
            if (fes)
                fes.func.setImpure();
        }
        else if (isPure())
            return true;
        return false;
    }

    final bool isSafe()
    {
        if (flags & FUNCFLAG.safetyInprocess)
            setUnsafe();
        return type.toTypeFunction().trust == TRUST.safe;
    }

    final bool isSafeBypassingInference()
    {
        return !(flags & FUNCFLAG.safetyInprocess) && isSafe();
    }

    final bool isTrusted()
    {
        if (flags & FUNCFLAG.safetyInprocess)
            setUnsafe();
        return type.toTypeFunction().trust == TRUST.trusted;
    }

    /**************************************
     * The function is doing something unsafe,
     * so mark it as unsafe.
     * If there's a safe error, return true.
     */
    extern (D) final bool setUnsafe()
    {
        if (flags & FUNCFLAG.safetyInprocess)
        {
            flags &= ~FUNCFLAG.safetyInprocess;
            type.toTypeFunction().trust = TRUST.system;
            if (fes)
                fes.func.setUnsafe();
        }
        else if (isSafe())
            return true;
        return false;
    }

    final bool isNogc()
    {
        //printf("isNogc() %s, inprocess: %d\n", toChars(), !!(flags & FUNCFLAG.nogcInprocess));
        if (flags & FUNCFLAG.nogcInprocess)
            setGC();
        return type.toTypeFunction().isnogc;
    }

    final bool isNogcBypassingInference()
    {
        return !(flags & FUNCFLAG.nogcInprocess) && isNogc();
    }

    /**************************************
     * The function is doing something that may allocate with the GC,
     * so mark it as not nogc (not no-how).
     * Returns:
     *      true if function is marked as @nogc, meaning a user error occurred
     */
    extern (D) final bool setGC()
    {
        //printf("setGC() %s\n", toChars());
        if (flags & FUNCFLAG.nogcInprocess && semanticRun < PASS.semantic3 && _scope)
        {
            this.semantic2(_scope);
            this.semantic3(_scope);
        }

        if (flags & FUNCFLAG.nogcInprocess)
        {
            flags &= ~FUNCFLAG.nogcInprocess;
            type.toTypeFunction().isnogc = false;
            if (fes)
                fes.func.setGC();
        }
        else if (isNogc())
            return true;
        return false;
    }

    extern (D) final void printGCUsage(const ref Loc loc, const(char)* warn)
    {
        if (!global.params.vgc)
            return;

        Module m = getModule();
        if (m && m.isRoot() && !inUnittest())
        {
            message(loc, "vgc: %s", warn);
        }
    }

    /********************************************
     * See if pointers from function parameters, mutable globals, or uplevel functions
     * could leak into return value.
     * Returns:
     *   true if the function return value is isolated from
     *   any inputs to the function
     */
    extern (D) final bool isReturnIsolated()
    {
        //printf("isReturnIsolated(this: %s)\n", this.toChars);
        TypeFunction tf = type.toTypeFunction();
        assert(tf.next);

        Type treti = tf.next;
        if (tf.isref)
            return isTypeIsolatedIndirect(treti);              // check influence from parameters

        return isTypeIsolated(treti);
    }

    /********************
     * See if pointers from function parameters, mutable globals, or uplevel functions
     * could leak into type `t`.
     * Params:
     *   t = type to check if it is isolated
     * Returns:
     *   true if `t` is isolated from
     *   any inputs to the function
     */
    extern (D) final bool isTypeIsolated(Type t)
    {
        StringTable!Type parentTypes;
        const uniqueTypeID = t.getUniqueID();
        if (uniqueTypeID)
        {
            const cacheResultPtr = uniqueTypeID in isTypeIsolatedCache;
            if (cacheResultPtr !is null)
                return *cacheResultPtr;

            parentTypes._init();
            const isIsolated = isTypeIsolated(t, parentTypes);
            isTypeIsolatedCache[uniqueTypeID] = isIsolated;
            return isIsolated;
        }
        else
        {
            parentTypes._init();
            return isTypeIsolated(t, parentTypes);
        }
    }

    ///ditto
    extern (D) final bool isTypeIsolated(Type t, ref StringTable!Type parentTypes)
    {
        //printf("this: %s, isTypeIsolated(t: %s)\n", this.toChars(), t.toChars());

        t = t.baseElemOf();
        switch (t.ty)
        {
            case Tarray:
            case Tpointer:
                return isTypeIsolatedIndirect(t.nextOf()); // go down one level

            case Taarray:
            case Tclass:
                return isTypeIsolatedIndirect(t);

            case Tstruct:
                /* Drill down and check the struct's fields
                 */
                auto sym = t.toDsymbol(null).isStructDeclaration();
                const tName = t.toChars.toDString;
                const entry = parentTypes.insert(tName, t);
                if (entry == null)
                {
                    //we've already seen this type in a parent, not isolated
                    return false;
                }
                foreach (v; sym.fields)
                {
                    Type tmi = v.type.addMod(t.mod);
                    //printf("\tt = %s, v: %s, vtype: %s,  tmi = %s\n",
                    //       t.toChars(), v.toChars(), v.type.toChars(), tmi.toChars());
                    if (!isTypeIsolated(tmi, parentTypes))
                        return false;
                }
                return true;

            default:
                return true;
        }
    }

    /********************************************
     * Params:
     *    t = type of object to test one level of indirection down
     * Returns:
     *    true if an object typed `t` has no indirections
     *    which could have come from the function's parameters, mutable
     *    globals, or uplevel functions.
     */
    private bool isTypeIsolatedIndirect(Type t)
    {
        //printf("isTypeIsolatedIndirect(t: %s)\n", t.toChars());
        assert(t);

        /* Since `t` is one level down from an indirection, it could pick
         * up a reference to a mutable global or an outer function, so
         * return false.
         */
        if (!isPureBypassingInference() || isNested())
            return false;

        TypeFunction tf = type.toTypeFunction();

        //printf("isTypeIsolatedIndirect(%s) t = %s\n", tf.toChars(), t.toChars());

        foreach (i, fparam; tf.parameterList)
        {
            Type tp = fparam.type;
            if (!tp)
                continue;

            if (fparam.storageClass & (STC.lazy_ | STC.out_ | STC.ref_))
            {
                if (!traverseIndirections(tp, t))
                    return false;
                continue;
            }

            /* Goes down one level of indirection, then calls traverseIndirection() on
             * the result.
             * Returns:
             *  true if t is isolated from tp
             */
            static bool traverse(Type tp, Type t)
            {
                tp = tp.baseElemOf();
                switch (tp.ty)
                {
                    case Tarray:
                    case Tpointer:
                        return traverseIndirections(tp.nextOf(), t);

                    case Taarray:
                    case Tclass:
                        return traverseIndirections(tp, t);

                    case Tstruct:
                        /* Drill down and check the struct's fields
                         */
                        auto sym = tp.toDsymbol(null).isStructDeclaration();
                        foreach (v; sym.fields)
                        {
                            Type tprmi = v.type.addMod(tp.mod);
                            //printf("\ttp = %s, tprmi = %s\n", tp.toChars(), tprmi.toChars());
                            if (!traverse(tprmi, t))
                                return false;
                        }
                        return true;

                    default:
                        return true;
                }
            }

            if (!traverse(tp, t))
                return false;
        }
        // The 'this' reference is a parameter, too
        if (AggregateDeclaration ad = isCtorDeclaration() ? null : isThis())
        {
            Type tthis = ad.getType().addMod(tf.mod);
            //printf("\ttthis = %s\n", tthis.toChars());
            if (!traverseIndirections(tthis, t))
                return false;
        }

        return true;
    }

    /****************************************
     * Determine if function needs a static frame pointer.
     * Returns:
     *  `true` if function is really nested within other function.
     * Contracts:
     *  If isNested() returns true, isThis() should return false,
     *  unless the function needs a dual-context pointer.
     */
    bool isNested() const
    {
        auto f = toAliasFunc();
        //printf("\ttoParent2() = '%s'\n", f.toParent2().toChars());
        return ((f.storage_class & STC.static_) == 0) &&
                (f.linkage == LINK.d) &&
                (f.toParent2().isFuncDeclaration() !is null ||
                 f.toParent2() !is f.toParentLocal());
    }

    /****************************************
     * Determine if function is a non-static member function
     * that has an implicit 'this' expression.
     * Returns:
     *  The aggregate it is a member of, or null.
     * Contracts:
     *  Both isThis() and isNested() should return true if function needs a dual-context pointer,
     *  otherwise if isThis() returns true, isNested() should return false.
     */
    override inout(AggregateDeclaration) isThis() inout
    {
        //printf("+FuncDeclaration::isThis() '%s'\n", toChars());
        auto ad = (storage_class & STC.static_) ? .objc.isThis(this) : isMemberLocal();
        //printf("-FuncDeclaration::isThis() %p\n", ad);
        return ad;
    }

    override final bool needThis()
    {
        //printf("FuncDeclaration::needThis() '%s'\n", toChars());
        return toAliasFunc().isThis() !is null;
    }

    // Determine if a function is pedantically virtual
    final bool isVirtualMethod()
    {
        if (toAliasFunc() != this)
            return toAliasFunc().isVirtualMethod();

        //printf("FuncDeclaration::isVirtualMethod() %s\n", toChars());
        if (!isVirtual())
            return false;
        // If it's a final method, and does not override anything, then it is not virtual
        if (isFinalFunc() && foverrides.dim == 0)
        {
            return false;
        }
        return true;
    }

    // Determine if function goes into virtual function pointer table
    bool isVirtual() const
    {
        if (toAliasFunc() != this)
            return toAliasFunc().isVirtual();

        auto p = toParent();

        if (!isMember || !p.isClassDeclaration)
            return false;

        if (p.isClassDeclaration.classKind == ClassKind.objc)
            return .objc.isVirtual(this);

        version (none)
        {
            printf("FuncDeclaration::isVirtual(%s)\n", toChars());
            printf("isMember:%p isStatic:%d private:%d ctor:%d !Dlinkage:%d\n", isMember(), isStatic(), visibility == Visibility.Kind.private_, isCtorDeclaration(), linkage != LINK.d);
            printf("result is %d\n", isMember() && !(isStatic() || visibility == Visibility.Kind.private_ || visibility == Visibility.Kind.package_) && p.isClassDeclaration() && !(p.isInterfaceDeclaration() && isFinalFunc()));
        }
        return !(isStatic() || visibility.kind == Visibility.Kind.private_ || visibility.kind == Visibility.Kind.package_) && !(p.isInterfaceDeclaration() && isFinalFunc());
    }

    final bool isFinalFunc() const
    {
        if (toAliasFunc() != this)
            return toAliasFunc().isFinalFunc();

        version (none)
        {{
            auto cd = toParent().isClassDeclaration();
            printf("FuncDeclaration::isFinalFunc(%s), %x\n", toChars(), Declaration.isFinal());
            printf("%p %d %d %d\n", isMember(), isStatic(), Declaration.isFinal(), ((cd = toParent().isClassDeclaration()) !is null && cd.storage_class & STC.final_));
            printf("result is %d\n", isMember() && (Declaration.isFinal() || (cd !is null && cd.storage_class & STC.final_)));
            if (cd)
                printf("\tmember of %s\n", cd.toChars());
        }}
        if (!isMember())
            return false;
        if (Declaration.isFinal())
            return true;
        auto cd = toParent().isClassDeclaration();
        return (cd !is null) && (cd.storage_class & STC.final_);
    }

    bool addPreInvariant()
    {
        auto ad = isThis();
        ClassDeclaration cd = ad ? ad.isClassDeclaration() : null;
        return (ad && !(cd && cd.isCPPclass()) && global.params.useInvariants == CHECKENABLE.on && (visibility.kind == Visibility.Kind.protected_ || visibility.kind == Visibility.Kind.public_ || visibility.kind == Visibility.Kind.export_) && !naked);
    }

    bool addPostInvariant()
    {
        auto ad = isThis();
        ClassDeclaration cd = ad ? ad.isClassDeclaration() : null;
        return (ad && !(cd && cd.isCPPclass()) && ad.inv && global.params.useInvariants == CHECKENABLE.on && (visibility.kind == Visibility.Kind.protected_ || visibility.kind == Visibility.Kind.public_ || visibility.kind == Visibility.Kind.export_) && !naked);
    }

    override const(char)* kind() const
    {
        return generated ? "generated function" : "function";
    }

    /********************************************
     * Returns:
     *  true if there are no overloads of this function
     */
    final bool isUnique() const
    {
        bool result = false;
        overloadApply(cast() this, (Dsymbol s)
        {
            auto f = s.isFuncDeclaration();
            if (!f)
                return 0;
            if (result)
            {
                result = false;
                return 1; // ambiguous, done
            }
            else
            {
                result = true;
                return 0;
            }
        });
        return result;
    }

    /*********************************************
     * In the current function, we are calling 'this' function.
     * 1. Check to see if the current function can call 'this' function, issue error if not.
     * 2. If the current function is not the parent of 'this' function, then add
     *    the current function to the list of siblings of 'this' function.
     * 3. If the current function is a literal, and it's accessing an uplevel scope,
     *    then mark it as a delegate.
     * Returns true if error occurs.
     */
    extern (D) final bool checkNestedReference(Scope* sc, const ref Loc loc)
    {
        //printf("FuncDeclaration::checkNestedReference() %s\n", toPrettyChars());

        if (auto fld = this.isFuncLiteralDeclaration())
        {
            if (fld.tok == TOK.reserved)
            {
                fld.tok = TOK.function_;
                fld.vthis = null;
            }
        }

        if (!parent || parent == sc.parent)
            return false;
        if (ident == Id.require || ident == Id.ensure)
            return false;
        if (!isThis() && !isNested())
            return false;

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

        Dsymbol p = toParentLocal();
        Dsymbol p2 = toParent2();

        // Function literals from fdthis to p must be delegates
        ensureStaticLinkTo(fdthis, p);
        if (p != p2)
            ensureStaticLinkTo(fdthis, p2);

        if (isNested())
        {
            // The function that this function is in
            bool checkEnclosing(FuncDeclaration fdv)
            {
                if (!fdv)
                    return false;
                if (fdv == fdthis)
                    return false;

                //printf("this = %s in [%s]\n", this.toChars(), this.loc.toChars());
                //printf("fdv  = %s in [%s]\n", fdv .toChars(), fdv .loc.toChars());
                //printf("fdthis = %s in [%s]\n", fdthis.toChars(), fdthis.loc.toChars());

                // Add this function to the list of those which called us
                if (fdthis != this)
                {
                    bool found = false;
                    for (size_t i = 0; i < siblingCallers.dim; ++i)
                    {
                        if (siblingCallers[i] == fdthis)
                            found = true;
                    }
                    if (!found)
                    {
                        //printf("\tadding sibling %s\n", fdthis.toPrettyChars());
                        if (!sc.intypeof && !(sc.flags & SCOPE.compile))
                            siblingCallers.push(fdthis);
                    }
                }

                const lv = fdthis.getLevelAndCheck(loc, sc, fdv, this);
                if (lv == LevelError)
                    return true; // error
                if (lv == -1)
                    return false; // downlevel call
                if (lv == 0)
                    return false; // same level call

                return false; // Uplevel call
            }

            if (checkEnclosing(p.isFuncDeclaration()))
                return true;
            if (checkEnclosing(p == p2 ? null : p2.isFuncDeclaration()))
                return true;
        }
        return false;
    }

    /*******************************
     * Look at all the variables in this function that are referenced
     * by nested functions, and determine if a closure needs to be
     * created for them.
     */
    final bool needsClosure()
    {
        /* Need a closure for all the closureVars[] if any of the
         * closureVars[] are accessed by a
         * function that escapes the scope of this function.
         * We take the conservative approach and decide that a function needs
         * a closure if it:
         * 1) is a virtual function
         * 2) has its address taken
         * 3) has a parent that escapes
         * 4) calls another nested function that needs a closure
         *
         * Note that since a non-virtual function can be called by
         * a virtual one, if that non-virtual function accesses a closure
         * var, the closure still has to be taken. Hence, we check for isThis()
         * instead of isVirtual(). (thanks to David Friedman)
         *
         * When the function returns a local struct or class, `requiresClosure`
         * is already set to `true` upon entering this function when the
         * struct/class refers to a local variable and a closure is needed.
         */

        //printf("FuncDeclaration::needsClosure() %s\n", toChars());

        if (requiresClosure)
            goto Lyes;

        for (size_t i = 0; i < closureVars.dim; i++)
        {
            VarDeclaration v = closureVars[i];
            //printf("\tv = %s\n", v.toChars());

            for (size_t j = 0; j < v.nestedrefs.dim; j++)
            {
                FuncDeclaration f = v.nestedrefs[j];
                assert(f != this);

                /* __require and __ensure will always get called directly,
                 * so they never make outer functions closure.
                 */
                if (f.ident == Id.require || f.ident == Id.ensure)
                    continue;

                //printf("\t\tf = %p, %s, isVirtual=%d, isThis=%p, tookAddressOf=%d\n", f, f.toChars(), f.isVirtual(), f.isThis(), f.tookAddressOf);

                /* Look to see if f escapes. We consider all parents of f within
                 * this, and also all siblings which call f; if any of them escape,
                 * so does f.
                 * Mark all affected functions as requiring closures.
                 */
                for (Dsymbol s = f; s && s != this; s = s.toParentP(this))
                {
                    FuncDeclaration fx = s.isFuncDeclaration();
                    if (!fx)
                        continue;
                    if (fx.isThis() || fx.tookAddressOf)
                    {
                        //printf("\t\tfx = %s, isVirtual=%d, isThis=%p, tookAddressOf=%d\n", fx.toChars(), fx.isVirtual(), fx.isThis(), fx.tookAddressOf);

                        /* Mark as needing closure any functions between this and f
                         */
                        markAsNeedingClosure((fx == f) ? fx.toParentP(this) : fx, this);

                        requiresClosure = true;
                    }

                    /* We also need to check if any sibling functions that
                     * called us, have escaped. This is recursive: we need
                     * to check the callers of our siblings.
                     */
                    if (checkEscapingSiblings(fx, this))
                        requiresClosure = true;

                    /* https://issues.dlang.org/show_bug.cgi?id=12406
                     * Iterate all closureVars to mark all descendant
                     * nested functions that access to the closing context of this function.
                     */
                }
            }
        }
        if (requiresClosure)
            goto Lyes;

        return false;

    Lyes:
        //printf("\tneeds closure\n");
        return true;
    }

    /***********************************************
     * Check that the function contains any closure.
     * If it's @nogc, report suitable errors.
     * This is mostly consistent with FuncDeclaration::needsClosure().
     *
     * Returns:
     *      true if any errors occur.
     */
    extern (D) final bool checkClosure()
    {
        if (!needsClosure())
            return false;

        if (setGC())
        {
            error("is `@nogc` yet allocates closures with the GC");
            if (global.gag)     // need not report supplemental errors
                return true;
        }
        else
        {
            printGCUsage(loc, "using closure causes GC allocation");
            return false;
        }

        FuncDeclarations a;
        foreach (v; closureVars)
        {
            foreach (f; v.nestedrefs)
            {
                assert(f !is this);

            LcheckAncestorsOfANestedRef:
                for (Dsymbol s = f; s && s !is this; s = s.toParentP(this))
                {
                    auto fx = s.isFuncDeclaration();
                    if (!fx)
                        continue;
                    if (fx.isThis() ||
                        fx.tookAddressOf ||
                        checkEscapingSiblings(fx, this))
                    {
                        foreach (f2; a)
                        {
                            if (f2 == f)
                                break LcheckAncestorsOfANestedRef;
                        }
                        a.push(f);
                        .errorSupplemental(f.loc, "%s closes over variable %s at %s",
                            f.toPrettyChars(), v.toChars(), v.loc.toChars());
                        break LcheckAncestorsOfANestedRef;
                    }
                }
            }
        }

        return true;
    }

    /***********************************************
     * Determine if function's variables are referenced by a function
     * nested within it.
     */
    final bool hasNestedFrameRefs()
    {
        if (closureVars.dim)
            return true;

        /* If a virtual function has contracts, assume its variables are referenced
         * by those contracts, even if they aren't. Because they might be referenced
         * by the overridden or overriding function's contracts.
         * This can happen because frequire and fensure are implemented as nested functions,
         * and they can be called directly by an overriding function and the overriding function's
         * context had better match, or
         * https://issues.dlang.org/show_bug.cgi?id=7335 will bite.
         */
        if (fdrequire || fdensure)
            return true;

        if (foverrides.dim && isVirtualMethod())
        {
            for (size_t i = 0; i < foverrides.dim; i++)
            {
                FuncDeclaration fdv = foverrides[i];
                if (fdv.hasNestedFrameRefs())
                    return true;
            }
        }
        return false;
    }

    /****************************************************
     * Check whether result variable can be built.
     * Returns:
     *     `true` if the function has a return type that
     *     is different from `void`.
     */
    extern (D) private bool canBuildResultVar()
    {
        auto f = cast(TypeFunction)type;
        return f && f.nextOf() && f.nextOf().toBasetype().ty != Tvoid;
    }

    /****************************************************
     * Declare result variable lazily.
     */
    extern (D) final void buildResultVar(Scope* sc, Type tret)
    {
        if (!vresult)
        {
            Loc loc = fensure ? fensure.loc : this.loc;

            /* If inferRetType is true, tret may not be a correct return type yet.
             * So, in here it may be a temporary type for vresult, and after
             * fbody.dsymbolSemantic() running, vresult.type might be modified.
             */
            vresult = new VarDeclaration(loc, tret, Id.result, null);
            vresult.storage_class |= STC.nodtor | STC.temp;
            if (!isVirtual())
                vresult.storage_class |= STC.const_;
            vresult.storage_class |= STC.result;

            // set before the semantic() for checkNestedReference()
            vresult.parent = this;
        }

        if (sc && vresult.semanticRun == PASS.init)
        {
            TypeFunction tf = type.toTypeFunction();
            if (tf.isref)
                vresult.storage_class |= STC.ref_;
            vresult.type = tret;

            vresult.dsymbolSemantic(sc);

            if (!sc.insert(vresult))
                error("out result %s is already defined", vresult.toChars());
            assert(vresult.parent == this);
        }
    }

    /****************************************************
     * Merge into this function the 'in' contracts of all it overrides.
     * 'in's are OR'd together, i.e. only one of them needs to pass.
     */
    extern (D) final Statement mergeFrequire(Statement sf, Expressions* params)
    {
        /* If a base function and its override both have an IN contract, then
         * only one of them needs to succeed. This is done by generating:
         *
         * void derived.in() {
         *  try {
         *    base.in();
         *  }
         *  catch () {
         *    ... body of derived.in() ...
         *  }
         * }
         *
         * So if base.in() doesn't throw, derived.in() need not be executed, and the contract is valid.
         * If base.in() throws, then derived.in()'s body is executed.
         */

        foreach (fdv; foverrides)
        {
            /* The semantic pass on the contracts of the overridden functions must
             * be completed before code generation occurs.
             * https://issues.dlang.org/show_bug.cgi?id=3602
             */
            if (fdv.frequires && fdv.semanticRun != PASS.semantic3done)
            {
                assert(fdv._scope);
                Scope* sc = fdv._scope.push();
                sc.stc &= ~STC.override_;
                fdv.semantic3(sc);
                sc.pop();
            }

            sf = fdv.mergeFrequire(sf, params);
            if (!sf || !fdv.fdrequire)
                return null;
            //printf("fdv.frequire: %s\n", fdv.frequire.toChars());
            /* Make the call:
                *   try { __require(params); }
                *   catch (Throwable) { frequire; }
                */
            params = Expression.arraySyntaxCopy(params);
            Expression e = new CallExp(loc, new VarExp(loc, fdv.fdrequire, false), params);
            Statement s2 = new ExpStatement(loc, e);

            auto c = new Catch(loc, getThrowable(), null, sf);
            c.internalCatch = true;
            auto catches = new Catches();
            catches.push(c);
            sf = new TryCatchStatement(loc, s2, catches);
        }
        return sf;
    }

    /****************************************************
     * Merge into this function the 'in' contracts of all it overrides.
     */
    extern (D) final Statement mergeFrequireInclusivePreview(Statement sf, Expressions* params)
    {
        /* If a base function and its override both have an IN contract, then
         * the override in contract must widen the guarantee of the base contract.
         * This is checked by generating:
         *
         * void derived.in() {
         *  try {
         *    ... body of derived.in() ...
         *  }
         *  catch () {
         *    // derived in rejected this argument. so parent must also reject it, or we've tightened the contract.
         *    base.in();
         *    assert(false, "Logic error: " ~ thr.msg);
         *  }
         */

        foreach (fdv; foverrides)
        {
            /* The semantic pass on the contracts of the overridden functions must
             * be completed before code generation occurs.
             * https://issues.dlang.org/show_bug.cgi?id=3602
             */
            if (fdv.frequires && fdv.semanticRun != PASS.semantic3done)
            {
                assert(fdv._scope);
                Scope* sc = fdv._scope.push();
                sc.stc &= ~STC.override_;
                fdv.semantic3(sc);
                sc.pop();
            }

            sf = fdv.mergeFrequireInclusivePreview(sf, params);
            if (sf && fdv.fdrequire)
            {
                const loc = this.fdrequire.loc;

                //printf("fdv.frequire: %s\n", fdv.frequire.toChars());
                /* Make the call:
                 *   try { frequire; }
                 *   catch (Throwable thr) { __require(params); assert(false, "Logic error: " ~ thr.msg); }
                 */
                Identifier id = Identifier.generateId("thr");
                params = Expression.arraySyntaxCopy(params);
                Expression e = new CallExp(loc, new VarExp(loc, fdv.fdrequire, false), params);
                Statement s2 = new ExpStatement(loc, e);
                // assert(false, ...)
                // TODO make this a runtime helper to allow:
                // - chaining the original expression
                // - nogc concatenation
                Expression msg = new StringExp(loc, "Logic error: in-contract was tighter than parent in-contract");
                Statement fail = new ExpStatement(loc, new AssertExp(loc, IntegerExp.literal!0, msg));

                Statement s3 = new CompoundStatement(loc, s2, fail);

                auto c = new Catch(loc, getThrowable(), id, s3);
                c.internalCatch = true;
                auto catches = new Catches();
                catches.push(c);
                sf = new TryCatchStatement(loc, sf, catches);
            }
            else
                return null;
        }
        return sf;
    }

    /****************************************************
     * Determine whether an 'out' contract is declared inside
     * the given function or any of its overrides.
     * Params:
     *      fd = the function to search
     * Returns:
     *      true    found an 'out' contract
     */
    static bool needsFensure(FuncDeclaration fd)
    {
        if (fd.fensures)
            return true;

        foreach (fdv; fd.foverrides)
        {
            if (needsFensure(fdv))
                return true;
        }
        return false;
    }

    /****************************************************
     * Rewrite contracts as statements.
     */
    final void buildEnsureRequire()
    {

        if (frequires)
        {
            /*   in { statements1... }
             *   in { statements2... }
             *   ...
             * becomes:
             *   in { { statements1... } { statements2... } ... }
             */
            assert(frequires.dim);
            auto loc = (*frequires)[0].loc;
            auto s = new Statements;
            foreach (r; *frequires)
            {
                s.push(new ScopeStatement(r.loc, r, r.loc));
            }
            frequire = new CompoundStatement(loc, s);
        }

        if (fensures)
        {
            /*   out(id1) { statements1... }
             *   out(id2) { statements2... }
             *   ...
             * becomes:
             *   out(__result) { { ref id1 = __result; { statements1... } }
             *                   { ref id2 = __result; { statements2... } } ... }
             */
            assert(fensures.dim);
            auto loc = (*fensures)[0].ensure.loc;
            auto s = new Statements;
            foreach (r; *fensures)
            {
                if (r.id && canBuildResultVar())
                {
                    auto rloc = r.ensure.loc;
                    auto resultId = new IdentifierExp(rloc, Id.result);
                    auto init = new ExpInitializer(rloc, resultId);
                    auto stc = STC.ref_ | STC.temp | STC.result;
                    auto decl = new VarDeclaration(rloc, null, r.id, init, stc);
                    auto sdecl = new ExpStatement(rloc, decl);
                    s.push(new ScopeStatement(rloc, new CompoundStatement(rloc, sdecl, r.ensure), rloc));
                }
                else
                {
                    s.push(r.ensure);
                }
            }
            fensure = new CompoundStatement(loc, s);
        }

        if (!isVirtual())
            return;

        /* Rewrite contracts as nested functions, then call them. Doing it as nested
         * functions means that overriding functions can call them.
         */
        TypeFunction f = cast(TypeFunction) type;

        /* Make a copy of the parameters and make them all ref */
        static Parameters* toRefCopy(ParameterList parameterList)
        {
            auto result = new Parameters();

            foreach (n, p; parameterList)
            {
                p = p.syntaxCopy();
                if (!(p.storageClass & STC.lazy_))
                    p.storageClass = (p.storageClass | STC.ref_) & ~STC.out_;
                p.defaultArg = null; // won't be the same with ref
                result.push(p);
            }

            return result;
        }

        if (frequire)
        {
            /*   in { ... }
             * becomes:
             *   void __require(ref params) { ... }
             *   __require(params);
             */
            Loc loc = frequire.loc;
            fdrequireParams = new Expressions();
            if (parameters)
            {
                foreach (vd; *parameters)
                    fdrequireParams.push(new VarExp(loc, vd));
            }
            auto fo = cast(TypeFunction)(originalType ? originalType : f);
            auto fparams = toRefCopy(fo.parameterList);
            auto tf = new TypeFunction(ParameterList(fparams), Type.tvoid, LINK.d);
            tf.isnothrow = f.isnothrow;
            tf.isnogc = f.isnogc;
            tf.purity = f.purity;
            tf.trust = f.trust;
            auto fd = new FuncDeclaration(loc, loc, Id.require, STC.undefined_, tf);
            fd.fbody = frequire;
            Statement s1 = new ExpStatement(loc, fd);
            Expression e = new CallExp(loc, new VarExp(loc, fd, false), fdrequireParams);
            Statement s2 = new ExpStatement(loc, e);
            frequire = new CompoundStatement(loc, s1, s2);
            fdrequire = fd;
        }

        /* We need to set fdensureParams here and not in the block below to
         * have the parameters available when calling a base class ensure(),
         * even if this function doesn't have an out contract.
         */
        fdensureParams = new Expressions();
        if (canBuildResultVar())
            fdensureParams.push(new IdentifierExp(loc, Id.result));
        if (parameters)
        {
            foreach (vd; *parameters)
                fdensureParams.push(new VarExp(loc, vd));
        }

        if (fensure)
        {
            /*   out (result) { ... }
             * becomes:
             *   void __ensure(ref tret result, ref params) { ... }
             *   __ensure(result, params);
             */
            Loc loc = fensure.loc;
            auto fparams = new Parameters();
            if (canBuildResultVar())
            {
                Parameter p = new Parameter(STC.ref_ | STC.const_, f.nextOf(), Id.result, null, null);
                fparams.push(p);
            }
            auto fo = cast(TypeFunction)(originalType ? originalType : f);
            fparams.pushSlice((*toRefCopy(fo.parameterList))[]);
            auto tf = new TypeFunction(ParameterList(fparams), Type.tvoid, LINK.d);
            tf.isnothrow = f.isnothrow;
            tf.isnogc = f.isnogc;
            tf.purity = f.purity;
            tf.trust = f.trust;
            auto fd = new FuncDeclaration(loc, loc, Id.ensure, STC.undefined_, tf);
            fd.fbody = fensure;
            Statement s1 = new ExpStatement(loc, fd);
            Expression e = new CallExp(loc, new VarExp(loc, fd, false), fdensureParams);
            Statement s2 = new ExpStatement(loc, e);
            fensure = new CompoundStatement(loc, s1, s2);
            fdensure = fd;
        }
    }

    /****************************************************
     * Merge into this function the 'out' contracts of all it overrides.
     * 'out's are AND'd together, i.e. all of them need to pass.
     */
    extern (D) final Statement mergeFensure(Statement sf, Identifier oid, Expressions* params)
    {
        /* Same comments as for mergeFrequire(), except that we take care
         * of generating a consistent reference to the 'result' local by
         * explicitly passing 'result' to the nested function as a reference
         * argument.
         * This won't work for the 'this' parameter as it would require changing
         * the semantic code for the nested function so that it looks on the parameter
         * list for the 'this' pointer, something that would need an unknown amount
         * of tweaking of various parts of the compiler that I'd rather leave alone.
         */
        foreach (fdv; foverrides)
        {
            /* The semantic pass on the contracts of the overridden functions must
             * be completed before code generation occurs.
             * https://issues.dlang.org/show_bug.cgi?id=3602 and
             * https://issues.dlang.org/show_bug.cgi?id=5230
             */
            if (needsFensure(fdv) && fdv.semanticRun != PASS.semantic3done)
            {
                assert(fdv._scope);
                Scope* sc = fdv._scope.push();
                sc.stc &= ~STC.override_;
                fdv.semantic3(sc);
                sc.pop();
            }

            sf = fdv.mergeFensure(sf, oid, params);
            if (fdv.fdensure)
            {
                //printf("fdv.fensure: %s\n", fdv.fensure.toChars());
                // Make the call: __ensure(result, params)
                params = Expression.arraySyntaxCopy(params);
                if (canBuildResultVar())
                {
                    Type t1 = fdv.type.nextOf().toBasetype();
                    Type t2 = this.type.nextOf().toBasetype();
                    if (t1.isBaseOf(t2, null))
                    {
                        /* Making temporary reference variable is necessary
                         * in covariant return.
                         * https://issues.dlang.org/show_bug.cgi?id=5204
                         * https://issues.dlang.org/show_bug.cgi?id=10479
                         */
                        Expression* eresult = &(*params)[0];
                        auto ei = new ExpInitializer(Loc.initial, *eresult);
                        auto v = new VarDeclaration(Loc.initial, t1, Identifier.generateId("__covres"), ei);
                        v.storage_class |= STC.temp;
                        auto de = new DeclarationExp(Loc.initial, v);
                        auto ve = new VarExp(Loc.initial, v);
                        *eresult = new CommaExp(Loc.initial, de, ve);
                    }
                }
                Expression e = new CallExp(loc, new VarExp(loc, fdv.fdensure, false), params);
                Statement s2 = new ExpStatement(loc, e);

                if (sf)
                {
                    sf = new CompoundStatement(sf.loc, s2, sf);
                }
                else
                    sf = s2;
            }
        }
        return sf;
    }

    /*********************************************
     * Returns: the function's parameter list, and whether
     * it is variadic or not.
     */
    final ParameterList getParameterList()
    {
        if (type)
        {
            TypeFunction fdtype = type.isTypeFunction();
            if (fdtype) // Could also be TypeError
                return fdtype.parameterList;
        }

        return ParameterList(null, VarArg.none);
    }

    /**********************************
     * Generate a FuncDeclaration for a runtime library function.
     */
    static FuncDeclaration genCfunc(Parameters* fparams, Type treturn, const(char)* name, StorageClass stc = 0)
    {
        return genCfunc(fparams, treturn, Identifier.idPool(name, cast(uint)strlen(name)), stc);
    }

    static FuncDeclaration genCfunc(Parameters* fparams, Type treturn, Identifier id, StorageClass stc = 0)
    {
        FuncDeclaration fd;
        TypeFunction tf;
        Dsymbol s;
        __gshared DsymbolTable st = null;

        //printf("genCfunc(name = '%s')\n", id.toChars());
        //printf("treturn\n\t"); treturn.print();

        // See if already in table
        if (!st)
            st = new DsymbolTable();
        s = st.lookup(id);
        if (s)
        {
            fd = s.isFuncDeclaration();
            assert(fd);
            assert(fd.type.nextOf().equals(treturn));
        }
        else
        {
            tf = new TypeFunction(ParameterList(fparams), treturn, LINK.c, stc);
            fd = new FuncDeclaration(Loc.initial, Loc.initial, id, STC.static_, tf);
            fd.visibility = Visibility(Visibility.Kind.public_);
            fd.linkage = LINK.c;

            st.insert(fd);
        }
        return fd;
    }

    /******************
     * Check parameters and return type of D main() function.
     * Issue error messages.
     */
    extern (D) final void checkDmain()
    {
        TypeFunction tf = type.toTypeFunction();
        const nparams = tf.parameterList.length;
        bool argerr;
        if (nparams == 1)
        {
            auto fparam0 = tf.parameterList[0];
            auto t = fparam0.type.toBasetype();
            if (t.ty != Tarray ||
                t.nextOf().ty != Tarray ||
                t.nextOf().nextOf().ty != Tchar ||
                fparam0.storageClass & (STC.out_ | STC.ref_ | STC.lazy_))
            {
                argerr = true;
            }
        }

        if (!tf.nextOf())
            // auto main(), check after semantic
            assert(this.inferRetType);
        else if (tf.nextOf().ty != Tint32 && tf.nextOf().ty != Tvoid && tf.nextOf().ty != Tnoreturn)
            error("must return `int`, `void` or `noreturn`, not `%s`", tf.nextOf().toChars());
        else if (tf.parameterList.varargs || nparams >= 2 || argerr)
            error("parameters must be `main()` or `main(string[] args)`");
    }

    /***********************************************
     * Check all return statements for a function to verify that returning
     * using NRVO is possible.
     *
     * Returns:
     *      `false` if the result cannot be returned by hidden reference.
     */
    final bool checkNRVO()
    {
        if (!nrvo_can || returns is null)
            return false;

        auto tf = type.toTypeFunction();
        if (tf.isref)
            return false;

        foreach (rs; *returns)
        {
            if (auto ve = rs.exp.isVarExp())
            {
                auto v = ve.var.isVarDeclaration();
                if (!v || v.isOut() || v.isRef())
                    return false;
                else if (nrvo_var is null)
                {
                    // Variables in the data segment (e.g. globals, TLS or not),
                    // parameters and closure variables cannot be NRVOed.
                    if (v.isDataseg() || v.isParameter() || v.toParent2() != this)
                        return false;
                    // The variable type needs to be equivalent to the return type.
                    if (!v.type.equivalent(tf.next))
                        return false;
                    //printf("Setting nrvo to %s\n", v.toChars());
                    nrvo_var = v;
                }
                else if (nrvo_var != v)
                    return false;
            }
            else //if (!exp.isLvalue())    // keep NRVO-ability
                return false;
        }
        return true;
    }

    override final inout(FuncDeclaration) isFuncDeclaration() inout
    {
        return this;
    }

    inout(FuncDeclaration) toAliasFunc() inout
    {
        return this;
    }

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

/********************************************************
 * Generate Expression to call the invariant.
 * Input:
 *      ad      aggregate with the invariant
 *      vthis   variable with 'this'
 * Returns:
 *      void expression that calls the invariant
 */
Expression addInvariant(AggregateDeclaration ad, VarDeclaration vthis)
{
    Expression e = null;
    // Call invariant directly only if it exists
    FuncDeclaration inv = ad.inv;
    ClassDeclaration cd = ad.isClassDeclaration();

    while (!inv && cd)
    {
        cd = cd.baseClass;
        if (!cd)
            break;
        inv = cd.inv;
    }
    if (inv)
    {
        version (all)
        {
            // Workaround for https://issues.dlang.org/show_bug.cgi?id=13394
            // For the correct mangling,
            // run attribute inference on inv if needed.
            inv.functionSemantic();
        }

        //e = new DsymbolExp(Loc.initial, inv);
        //e = new CallExp(Loc.initial, e);
        //e = e.semantic(sc2);

        /* https://issues.dlang.org/show_bug.cgi?id=13113
         * Currently virtual invariant calls completely
         * bypass attribute enforcement.
         * Change the behavior of pre-invariant call by following it.
         */
        e = new ThisExp(Loc.initial);
        e.type = ad.type.addMod(vthis.type.mod);
        e = new DotVarExp(Loc.initial, e, inv, false);
        e.type = inv.type;
        e = new CallExp(Loc.initial, e);
        e.type = Type.tvoid;
    }
    return e;
}

/***************************************************
 * Visit each overloaded function/template in turn, and call dg(s) on it.
 * Exit when no more, or dg(s) returns nonzero.
 *
 * Params:
 *  fstart = symbol to start from
 *  dg = the delegate to be called on the overload
 *  sc = context used to check if symbol is accessible (and therefore visible),
 *       can be null
 *
 * Returns:
 *      ==0     continue
 *      !=0     done (and the return value from the last dg() call)
 */
extern (D) int overloadApply(Dsymbol fstart, scope int delegate(Dsymbol) dg, Scope* sc = null)
{
    Dsymbol next;
    for (auto d = fstart; d; d = next)
    {
        import dmd.access : checkSymbolAccess;
        if (auto od = d.isOverDeclaration())
        {
            /* The scope is needed here to check whether a function in
               an overload set was added by means of a private alias (or a
               selective import). If the scope where the alias is created
               is imported somewhere, the overload set is visible, but the private
               alias is not.
            */
            if (sc)
            {
                if (checkSymbolAccess(sc, od))
                {
                    if (int r = overloadApply(od.aliassym, dg, sc))
                        return r;
                }
            }
            else if (int r = overloadApply(od.aliassym, dg, sc))
                return r;
            next = od.overnext;
        }
        else if (auto fa = d.isFuncAliasDeclaration())
        {
            if (fa.hasOverloads)
            {
                if (int r = overloadApply(fa.funcalias, dg, sc))
                    return r;
            }
            else if (auto fd = fa.toAliasFunc())
            {
                if (int r = dg(fd))
                    return r;
            }
            else
            {
                d.error("is aliased to a function");
                break;
            }
            next = fa.overnext;
        }
        else if (auto ad = d.isAliasDeclaration())
        {
            if (sc)
            {
                if (checkSymbolAccess(sc, ad))
                    next = ad.toAlias();
            }
            else
               next = ad.toAlias();
            if (next == ad)
                break;
            if (next == fstart)
                break;
        }
        else if (auto td = d.isTemplateDeclaration())
        {
            if (int r = dg(td))
                return r;
            next = td.overnext;
        }
        else if (auto fd = d.isFuncDeclaration())
        {
            if (int r = dg(fd))
                return r;
            next = fd.overnext;
        }
        else if (auto os = d.isOverloadSet())
        {
            foreach (ds; os.a)
                if (int r = dg(ds))
                    return r;
        }
        else
        {
            d.error("is aliased to a function");
            break;
            // BUG: should print error message?
        }
    }
    return 0;
}

/**
Checks for mismatching modifiers between `lhsMod` and `rhsMod` and prints the
mismatching modifiers to `buf`.

The modifiers of the `lhsMod` mismatching the ones with the `rhsMod` are printed, i.e.
lhs(shared) vs. rhs() prints "`shared`", wheras lhs() vs rhs(shared) prints "non-shared".

Params:
    buf = output buffer to write to
    lhsMod = modifier on the left-hand side
    lhsMod = modifier on the right-hand side

Returns:

A tuple with `isMutable` and `isNotShared` set
if the `lhsMod` is missing those modifiers (compared to rhs).
*/
auto MODMatchToBuffer(OutBuffer* buf, ubyte lhsMod, ubyte rhsMod)
{
    static struct Mismatches
    {
        bool isNotShared;
        bool isMutable;
    }

    Mismatches mismatches;

    bool bothMutable = ((lhsMod & rhsMod) == 0);
    bool sharedMismatch = ((lhsMod ^ rhsMod) & MODFlags.shared_) != 0;
    bool sharedMismatchOnly = ((lhsMod ^ rhsMod) == MODFlags.shared_);

    if (lhsMod & MODFlags.shared_)
        buf.writestring("`shared` ");
    else if (sharedMismatch && !(lhsMod & MODFlags.immutable_))
    {
        buf.writestring("non-shared ");
        mismatches.isNotShared = true;
    }

    if (bothMutable && sharedMismatchOnly)
    {
    }
    else if (lhsMod & MODFlags.immutable_)
        buf.writestring("`immutable` ");
    else if (lhsMod & MODFlags.const_)
        buf.writestring("`const` ");
    else if (lhsMod & MODFlags.wild)
        buf.writestring("`inout` ");
    else
    {
        buf.writestring("mutable ");
        mismatches.isMutable = true;
    }

    return mismatches;
}

///
unittest
{
    OutBuffer buf;
    auto mismatches = MODMatchToBuffer(&buf, MODFlags.shared_, 0);
    assert(buf[] == "`shared` ");
    assert(!mismatches.isNotShared);

    buf.setsize(0);
    mismatches = MODMatchToBuffer(&buf, 0, MODFlags.shared_);
    assert(buf[] == "non-shared ");
    assert(mismatches.isNotShared);

    buf.setsize(0);
    mismatches = MODMatchToBuffer(&buf, MODFlags.const_, 0);
    assert(buf[] == "`const` ");
    assert(!mismatches.isMutable);

    buf.setsize(0);
    mismatches = MODMatchToBuffer(&buf, 0, MODFlags.const_);
    assert(buf[] == "mutable ");
    assert(mismatches.isMutable);
}

private const(char)* prependSpace(const(char)* str)
{
    if (!str || !*str) return "";

    return (" " ~ str.toDString() ~ "\0").ptr;
}

/// Flag used by $(LREF resolveFuncCall).
enum FuncResolveFlag : ubyte
{
    standard = 0,       /// issue error messages, solve the call.
    quiet = 1,          /// do not issue error message on no match, just return `null`.
    overloadOnly = 2,   /// only resolve overloads, i.e. do not issue error on ambiguous
                        /// matches and need explicit this.
}

/*******************************************
 * Given a symbol that could be either a FuncDeclaration or
 * a function template, resolve it to a function symbol.
 * Params:
 *      loc =           instantiation location
 *      sc =            instantiation scope
 *      s =             instantiation symbol
 *      tiargs =        initial list of template arguments
 *      tthis =         if !NULL, the `this` argument type
 *      fargs =         arguments to function
 *      flags =         see $(LREF FuncResolveFlag).
 * Returns:
 *      if match is found, then function symbol, else null
 */
FuncDeclaration resolveFuncCall(const ref Loc loc, Scope* sc, Dsymbol s,
    Objects* tiargs, Type tthis, Expressions* fargs, FuncResolveFlag flags)
{
    if (!s)
        return null; // no match

    version (none)
    {
        printf("resolveFuncCall('%s')\n", s.toChars());
        if (tthis)
            printf("\tthis: %s\n", tthis.toChars());
        if (fargs)
        {
            for (size_t i = 0; i < fargs.dim; i++)
            {
                Expression arg = (*fargs)[i];
                assert(arg.type);
                printf("\t%s: %s\n", arg.toChars(), arg.type.toChars());
            }
        }
    }

    if (tiargs && arrayObjectIsError(tiargs) ||
        fargs && arrayObjectIsError(cast(Objects*)fargs))
    {
        return null;
    }

    MatchAccumulator m;
    functionResolve(m, s, loc, sc, tiargs, tthis, fargs, null);
    auto orig_s = s;

    if (m.last > MATCH.nomatch && m.lastf)
    {
        if (m.count == 1) // exactly one match
        {
            if (!(flags & FuncResolveFlag.quiet))
                m.lastf.functionSemantic();
            return m.lastf;
        }
        if ((flags & FuncResolveFlag.overloadOnly) && !tthis && m.lastf.needThis())
        {
            return m.lastf;
        }
    }

    /* Failed to find a best match.
     * Do nothing or print error.
     */
    if (m.last == MATCH.nomatch)
    {
        // error was caused on matched function, not on the matching itself,
        // so return the function to produce a better diagnostic
        if (m.count == 1)
            return m.lastf;
    }

    // We are done at this point, as the rest of this function generate
    // a diagnostic on invalid match
    if (flags & FuncResolveFlag.quiet)
        return null;

    auto fd = s.isFuncDeclaration();
    auto od = s.isOverDeclaration();
    auto td = s.isTemplateDeclaration();
    if (td && td.funcroot)
        s = fd = td.funcroot;

    OutBuffer tiargsBuf;
    arrayObjectsToBuffer(&tiargsBuf, tiargs);

    OutBuffer fargsBuf;
    fargsBuf.writeByte('(');
    argExpTypesToCBuffer(&fargsBuf, fargs);
    fargsBuf.writeByte(')');
    if (tthis)
        tthis.modToBuffer(&fargsBuf);

    // The call is ambiguous
    if (m.lastf && m.nextf)
    {
        TypeFunction tf1 = m.lastf.type.toTypeFunction();
        TypeFunction tf2 = m.nextf.type.toTypeFunction();
        const(char)* lastprms = parametersTypeToChars(tf1.parameterList);
        const(char)* nextprms = parametersTypeToChars(tf2.parameterList);

        const(char)* mod1 = prependSpace(MODtoChars(tf1.mod));
        const(char)* mod2 = prependSpace(MODtoChars(tf2.mod));

        .error(loc, "`%s.%s` called with argument types `%s` matches both:\n%s:     `%s%s%s`\nand:\n%s:     `%s%s%s`",
            s.parent.toPrettyChars(), s.ident.toChars(),
            fargsBuf.peekChars(),
            m.lastf.loc.toChars(), m.lastf.toPrettyChars(), lastprms, mod1,
            m.nextf.loc.toChars(), m.nextf.toPrettyChars(), nextprms, mod2);
        return null;
    }

    // no match, generate an error messages
    if (!fd)
    {
        // all of overloads are templates
        if (td)
        {
            .error(loc, "%s `%s.%s` cannot deduce function from argument types `!(%s)%s`",
                   td.kind(), td.parent.toPrettyChars(), td.ident.toChars(),
                   tiargsBuf.peekChars(), fargsBuf.peekChars());

            printCandidates(loc, td, sc.isDeprecated());
            return null;
        }
        /* This case used to happen when several ctors are mixed in an agregate.
           A (bad) error message is already generated in overloadApply().
           see https://issues.dlang.org/show_bug.cgi?id=19729
           and https://issues.dlang.org/show_bug.cgi?id=17259
        */
        if (!od)
            return null;
    }

    if (od)
    {
        .error(loc, "none of the overloads of `%s` are callable using argument types `!(%s)%s`",
               od.ident.toChars(), tiargsBuf.peekChars(), fargsBuf.peekChars());
        return null;
    }

    // remove when deprecation period of class allocators and deallocators is over
    if (fd.isNewDeclaration() && fd.checkDisabled(loc, sc))
        return null;

    bool hasOverloads = fd.overnext !is null;
    auto tf = fd.type.isTypeFunction();
    // if type is an error, the original type should be there for better diagnostics
    if (!tf)
        tf = fd.originalType.toTypeFunction();

    if (tthis && !MODimplicitConv(tthis.mod, tf.mod)) // modifier mismatch
    {
        OutBuffer thisBuf, funcBuf;
        MODMatchToBuffer(&thisBuf, tthis.mod, tf.mod);
        auto mismatches = MODMatchToBuffer(&funcBuf, tf.mod, tthis.mod);
        if (hasOverloads)
        {
            .error(loc, "none of the overloads of `%s` are callable using a %sobject",
                   fd.ident.toChars(), thisBuf.peekChars());
            printCandidates(loc, fd, sc.isDeprecated());
            return null;
        }

        const(char)* failMessage;
        functionResolve(m, orig_s, loc, sc, tiargs, tthis, fargs, &failMessage);
        if (failMessage)
        {
            .error(loc, "%s `%s%s%s` is not callable using argument types `%s`",
                   fd.kind(), fd.toPrettyChars(), parametersTypeToChars(tf.parameterList),
                   tf.modToChars(), fargsBuf.peekChars());
            errorSupplemental(loc, failMessage);
            return null;
        }

        .error(loc, "%smethod `%s` is not callable using a %sobject",
               funcBuf.peekChars(), fd.toPrettyChars(), thisBuf.peekChars());

        if (mismatches.isNotShared)
            .errorSupplemental(fd.loc, "Consider adding `shared` here");
        else if (mismatches.isMutable)
            .errorSupplemental(fd.loc, "Consider adding `const` or `inout` here");
        return null;
    }

    //printf("tf = %s, args = %s\n", tf.deco, (*fargs)[0].type.deco);
    if (hasOverloads)
    {
        .error(loc, "none of the overloads of `%s` are callable using argument types `%s`",
               fd.toChars(), fargsBuf.peekChars());
        printCandidates(loc, fd, sc.isDeprecated());
        return null;
    }

    .error(loc, "%s `%s%s%s` is not callable using argument types `%s`",
           fd.kind(), fd.toPrettyChars(), parametersTypeToChars(tf.parameterList),
           tf.modToChars(), fargsBuf.peekChars());
    // re-resolve to check for supplemental message
    const(char)* failMessage;
    functionResolve(m, orig_s, loc, sc, tiargs, tthis, fargs, &failMessage);
    if (failMessage)
        errorSupplemental(loc, failMessage);
    return null;
}

/*******************************************
 * Prints template and function overload candidates as supplemental errors.
 * Params:
 *      loc =            instantiation location
 *      declaration =    the declaration to print overload candidates for
 *      showDeprecated = If `false`, `deprecated` function won't be shown
 */
private void printCandidates(Decl)(const ref Loc loc, Decl declaration, bool showDeprecated)
if (is(Decl == TemplateDeclaration) || is(Decl == FuncDeclaration))
{
    // max num of overloads to print (-v overrides this).
    enum int DisplayLimit = 5;
    int displayed;
    const(char)* constraintsTip;

    // determine if the first candidate was printed
    bool printed = false;

    overloadApply(declaration, (Dsymbol s)
    {
        Dsymbol nextOverload;

        if (auto fd = s.isFuncDeclaration())
        {
            // Don't print overloads which have errors.
            // Not that if the whole overload set has errors, we'll never reach
            // this point so there's no risk of printing no candidate
            if (fd.errors || fd.type.ty == Terror)
                return 0;
            // Don't print disabled functions, or `deprecated` outside of deprecated scope
            if (fd.storage_class & STC.disable || (fd.isDeprecated() && !showDeprecated))
                return 0;

            const single_candidate = fd.overnext is null;
            auto tf = cast(TypeFunction) fd.type;
            .errorSupplemental(fd.loc,
                    printed ? "                `%s%s`" :
                    single_candidate ? "Candidate is: `%s%s`" : "Candidates are: `%s%s`",
                    fd.toPrettyChars(),
                parametersTypeToChars(tf.parameterList));
            printed = true;
            nextOverload = fd.overnext;
        }
        else if (auto td = s.isTemplateDeclaration())
        {
            import dmd.staticcond;

            const tmsg = td.toCharsNoConstraints();
            const cmsg = td.getConstraintEvalError(constraintsTip);

            const single_candidate = td.overnext is null;

            // add blank space if there are multiple candidates
            // the length of the blank space is `strlen("Candidates are: ")`

            if (cmsg)
            {
                .errorSupplemental(td.loc,
                        printed ? "                `%s`\n%s" :
                        single_candidate ? "Candidate is: `%s`\n%s" : "Candidates are: `%s`\n%s",
                        tmsg, cmsg);
                printed = true;
            }
            else
            {
                .errorSupplemental(td.loc,
                        printed ? "                `%s`" :
                        single_candidate ? "Candidate is: `%s`" : "Candidates are: `%s`",
                        tmsg);
                printed = true;
            }
            nextOverload = td.overnext;
        }

        if (global.params.verbose || ++displayed < DisplayLimit)
            return 0;

        // Too many overloads to sensibly display.
        // Just show count of remaining overloads.
        int num = 0;
        overloadApply(nextOverload, (s) { ++num; return 0; });

        if (num > 0)
            .errorSupplemental(loc, "... (%d more, -v to show) ...", num);
        return 1;   // stop iterating
    });

    // Nothing was displayed, all overloads are either disabled or deprecated
    if (!displayed)
        .errorSupplemental(loc, "All possible candidates are marked as `deprecated` or `@disable`");
    // should be only in verbose mode
    if (constraintsTip)
        .tip(constraintsTip);
}

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

    // should consider TypeDelegate?
    return null;
}

/**************************************
 * Performs type-based alias analysis between a newly created value and a pre-
 * existing memory reference:
 *
 * Assuming that a reference A to a value of type `ta` was available to the code
 * that created a reference B to a value of type `tb`, it returns whether B
 * might alias memory reachable from A based on the types involved (either
 * directly or via any number of indirections in either A or B).
 *
 * This relation is not symmetric in the two arguments. For example, a
 * a `const(int)` reference can point to a pre-existing `int`, but not the other
 * way round.
 *
 * Examples:
 *
 *      ta,           tb,               result
 *      `const(int)`, `int`,            `false`
 *      `int`,        `const(int)`,     `true`
 *      `int`,        `immutable(int)`, `false`
 *      const(immutable(int)*), immutable(int)*, false   // BUG: returns true
 *
 * Params:
 *      ta = value type being referred to
 *      tb = referred to value type that could be constructed from ta
 *
 * Returns:
 *      true if reference to `tb` is isolated from reference to `ta`
 */
private bool traverseIndirections(Type ta, Type tb)
{
    //printf("traverseIndirections(%s, %s)\n", ta.toChars(), tb.toChars());

    static bool traverse(Type ta, Type tb, ref scope AssocArray!(const(char)*, bool) table, bool reversePass)
    {
        //printf("traverse(%s, %s)\n", ta.toChars(), tb.toChars());
        ta = ta.baseElemOf();
        tb = tb.baseElemOf();

        // First, check if the pointed-to types are convertible to each other such
        // that they might alias directly.
        static bool mayAliasDirect(Type source, Type target)
        {
            return
                // if source is the same as target or can be const-converted to target
                source.constConv(target) != MATCH.nomatch ||
                // if target is void and source can be const-converted to target
                (target.ty == Tvoid && MODimplicitConv(source.mod, target.mod));
        }

        if (mayAliasDirect(reversePass ? tb : ta, reversePass ? ta : tb))
        {
            //printf(" true  mayalias %s %s %d\n", ta.toChars(), tb.toChars(), reversePass);
            return false;
        }
        if (ta.nextOf() && ta.nextOf() == tb.nextOf())
        {
             //printf(" next==next %s %s %d\n", ta.toChars(), tb.toChars(), reversePass);
             return true;
        }

        if (tb.ty == Tclass || tb.ty == Tstruct)
        {
            /* Traverse the type of each field of the aggregate
             */
            bool* found = table.getLvalue(tb.deco);
            if (*found == true)
                return true; // We have already seen this symbol, break the cycle
            else
                *found = true;

            AggregateDeclaration sym = tb.toDsymbol(null).isAggregateDeclaration();
            foreach (v; sym.fields)
            {
                Type tprmi = v.type.addMod(tb.mod);
                //printf("\ttb = %s, tprmi = %s\n", tb.toChars(), tprmi.toChars());
                if (!traverse(ta, tprmi, table, reversePass))
                    return false;
            }
        }
        else if (tb.ty == Tarray || tb.ty == Taarray || tb.ty == Tpointer)
        {
            Type tind = tb.nextOf();
            if (!traverse(ta, tind, table, reversePass))
                return false;
        }
        else if (tb.hasPointers())
        {
            // BUG: consider the context pointer of delegate types
            return false;
        }

        // Still no match, so try breaking up ta if we have not done so yet.
        if (!reversePass)
        {
            scope newTable = AssocArray!(const(char)*, bool)();
            return traverse(tb, ta, newTable, true);
        }

        return true;
    }

    // To handle arbitrary levels of indirections in both parameters, we
    // recursively descend into aggregate members/levels of indirection in both
    // `ta` and `tb` while avoiding cycles. Start with the original types.
    scope table = AssocArray!(const(char)*, bool)();
    const result = traverse(ta, tb, table, false);
    //printf("  returns %d\n", result);
    return result;
}

/* For all functions between outerFunc and f, mark them as needing
 * a closure.
 */
private void markAsNeedingClosure(Dsymbol f, FuncDeclaration outerFunc)
{
    for (Dsymbol sx = f; sx && sx != outerFunc; sx = sx.toParentP(outerFunc))
    {
        FuncDeclaration fy = sx.isFuncDeclaration();
        if (fy && fy.closureVars.dim)
        {
            /* fy needs a closure if it has closureVars[],
             * because the frame pointer in the closure will be accessed.
             */
            fy.requiresClosure = true;
        }
    }
}

/********
 * Given a nested function f inside a function outerFunc, check
 * if any sibling callers of f have escaped. If so, mark
 * all the enclosing functions as needing closures.
 * This is recursive: we need to check the callers of our siblings.
 * Note that nested functions can only call lexically earlier nested
 * functions, so loops are impossible.
 * Params:
 *      f = inner function (nested within outerFunc)
 *      outerFunc = outer function
 *      p = for internal recursion use
 * Returns:
 *      true if any closures were needed
 */
private bool checkEscapingSiblings(FuncDeclaration f, FuncDeclaration outerFunc, void* p = null)
{
    static struct PrevSibling
    {
        PrevSibling* p;
        FuncDeclaration f;
    }

    PrevSibling ps;
    ps.p = cast(PrevSibling*)p;
    ps.f = f;

    //printf("checkEscapingSiblings(f = %s, outerfunc = %s)\n", f.toChars(), outerFunc.toChars());
    bool bAnyClosures = false;
    for (size_t i = 0; i < f.siblingCallers.dim; ++i)
    {
        FuncDeclaration g = f.siblingCallers[i];
        if (g.isThis() || g.tookAddressOf)
        {
            markAsNeedingClosure(g, outerFunc);
            bAnyClosures = true;
        }

        for (auto parent = g.toParentP(outerFunc); parent && parent !is outerFunc; parent = parent.toParentP(outerFunc))
        {
            // A parent of the sibling had its address taken.
            // Assume escaping of parent affects its children, so needs propagating.
            // see https://issues.dlang.org/show_bug.cgi?id=19679
            FuncDeclaration parentFunc = parent.isFuncDeclaration;
            if (parentFunc && parentFunc.tookAddressOf)
            {
                markAsNeedingClosure(parentFunc, outerFunc);
                bAnyClosures = true;
            }
        }

        PrevSibling* prev = cast(PrevSibling*)p;
        while (1)
        {
            if (!prev)
            {
                bAnyClosures |= checkEscapingSiblings(g, outerFunc, &ps);
                break;
            }
            if (prev.f == g)
                break;
            prev = prev.p;
        }
    }
    //printf("\t%d\n", bAnyClosures);
    return bAnyClosures;
}

/***********************************************************
 * Used as a way to import a set of functions from another scope into this one.
 */
extern (C++) final class FuncAliasDeclaration : FuncDeclaration
{
    FuncDeclaration funcalias;
    bool hasOverloads;

    extern (D) this(Identifier ident, FuncDeclaration funcalias, bool hasOverloads = true)
    {
        super(funcalias.loc, funcalias.endloc, ident, funcalias.storage_class, funcalias.type);
        assert(funcalias != this);
        this.funcalias = funcalias;

        this.hasOverloads = hasOverloads;
        if (hasOverloads)
        {
            if (FuncAliasDeclaration fad = funcalias.isFuncAliasDeclaration())
                this.hasOverloads = fad.hasOverloads;
        }
        else
        {
            // for internal use
            assert(!funcalias.isFuncAliasDeclaration());
            this.hasOverloads = false;
        }
        userAttribDecl = funcalias.userAttribDecl;
    }

    override inout(FuncAliasDeclaration) isFuncAliasDeclaration() inout
    {
        return this;
    }

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

    override inout(FuncDeclaration) toAliasFunc() inout
    {
        return funcalias.toAliasFunc();
    }

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

/***********************************************************
 */
extern (C++) final class FuncLiteralDeclaration : FuncDeclaration
{
    TOK tok;        // TOK.function_ or TOK.delegate_
    Type treq;      // target of return type inference

    // backend
    bool deferToObj;

    extern (D) this(const ref Loc loc, const ref Loc endloc, Type type, TOK tok, ForeachStatement fes, Identifier id = null)
    {
        super(loc, endloc, null, STC.undefined_, type);
        this.ident = id ? id : Id.empty;
        this.tok = tok;
        this.fes = fes;
        // Always infer scope for function literals
        // See https://issues.dlang.org/show_bug.cgi?id=20362
        this.flags |= FUNCFLAG.inferScope;
        //printf("FuncLiteralDeclaration() id = '%s', type = '%s'\n", this.ident.toChars(), type.toChars());
    }

    override FuncLiteralDeclaration syntaxCopy(Dsymbol s)
    {
        //printf("FuncLiteralDeclaration::syntaxCopy('%s')\n", toChars());
        assert(!s);
        auto f = new FuncLiteralDeclaration(loc, endloc, type.syntaxCopy(), tok, fes, ident);
        f.treq = treq; // don't need to copy
        FuncDeclaration.syntaxCopy(f);
        return f;
    }

    override bool isNested() const
    {
        //printf("FuncLiteralDeclaration::isNested() '%s'\n", toChars());
        return (tok != TOK.function_) && !isThis();
    }

    override inout(AggregateDeclaration) isThis() inout
    {
        return tok == TOK.delegate_ ? super.isThis() : null;
    }

    override bool isVirtual() const
    {
        return false;
    }

    override bool addPreInvariant()
    {
        return false;
    }

    override bool addPostInvariant()
    {
        return false;
    }

    /*******************************
     * Modify all expression type of return statements to tret.
     *
     * On function literals, return type may be modified based on the context type
     * after its semantic3 is done, in FuncExp::implicitCastTo.
     *
     *  A function() dg = (){ return new B(); } // OK if is(B : A) == true
     *
     * If B to A conversion is convariant that requires offseet adjusting,
     * all return statements should be adjusted to return expressions typed A.
     */
    void modifyReturns(Scope* sc, Type tret)
    {
        import dmd.statement_rewrite_walker;

        extern (C++) final class RetWalker : StatementRewriteWalker
        {
            alias visit = typeof(super).visit;
        public:
            Scope* sc;
            Type tret;
            FuncLiteralDeclaration fld;

            override void visit(ReturnStatement s)
            {
                Expression exp = s.exp;
                if (exp && !exp.type.equals(tret))
                {
                    s.exp = exp.castTo(sc, tret);
                }
            }
        }

        if (semanticRun < PASS.semantic3done)
            return;

        if (fes)
            return;

        scope RetWalker w = new RetWalker();
        w.sc = sc;
        w.tret = tret;
        w.fld = this;
        fbody.accept(w);

        // Also update the inferred function type to match the new return type.
        // This is required so the code generator does not try to cast the
        // modified returns back to the original type.
        if (inferRetType && type.nextOf() != tret)
            type.toTypeFunction().next = tret;
    }

    override inout(FuncLiteralDeclaration) isFuncLiteralDeclaration() inout
    {
        return this;
    }

    override const(char)* kind() const
    {
        // GCC requires the (char*) casts
        return (tok != TOK.function_) ? "delegate" : "function";
    }

    override const(char)* toPrettyChars(bool QualifyTypes = false)
    {
        if (parent)
        {
            TemplateInstance ti = parent.isTemplateInstance();
            if (ti)
                return ti.tempdecl.toPrettyChars(QualifyTypes);
        }
        return Dsymbol.toPrettyChars(QualifyTypes);
    }

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

/***********************************************************
 */
extern (C++) final class CtorDeclaration : FuncDeclaration
{
    bool isCpCtor;
    extern (D) this(const ref Loc loc, const ref Loc endloc, StorageClass stc, Type type, bool isCpCtor = false)
    {
        super(loc, endloc, Id.ctor, stc, type);
        this.isCpCtor = isCpCtor;
        //printf("CtorDeclaration(loc = %s) %s\n", loc.toChars(), toChars());
    }

    override CtorDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto f = new CtorDeclaration(loc, endloc, storage_class, type.syntaxCopy());
        FuncDeclaration.syntaxCopy(f);
        return f;
    }

    override const(char)* kind() const
    {
        return isCpCtor ? "copy constructor" : "constructor";
    }

    override const(char)* toChars() const
    {
        return "this";
    }

    override bool isVirtual() const
    {
        return false;
    }

    override bool addPreInvariant()
    {
        return false;
    }

    override bool addPostInvariant()
    {
        return (isThis() && vthis && global.params.useInvariants == CHECKENABLE.on);
    }

    override inout(CtorDeclaration) isCtorDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) final class PostBlitDeclaration : FuncDeclaration
{
    extern (D) this(const ref Loc loc, const ref Loc endloc, StorageClass stc, Identifier id)
    {
        super(loc, endloc, id, stc, null);
    }

    override PostBlitDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto dd = new PostBlitDeclaration(loc, endloc, storage_class, ident);
        FuncDeclaration.syntaxCopy(dd);
        return dd;
    }

    override bool isVirtual() const
    {
        return false;
    }

    override bool addPreInvariant()
    {
        return false;
    }

    override bool addPostInvariant()
    {
        return (isThis() && vthis && global.params.useInvariants == CHECKENABLE.on);
    }

    override bool overloadInsert(Dsymbol s)
    {
        return false; // cannot overload postblits
    }

    override inout(PostBlitDeclaration) isPostBlitDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) final class DtorDeclaration : FuncDeclaration
{
    extern (D) this(const ref Loc loc, const ref Loc endloc)
    {
        super(loc, endloc, Id.dtor, STC.undefined_, null);
    }

    extern (D) this(const ref Loc loc, const ref Loc endloc, StorageClass stc, Identifier id)
    {
        super(loc, endloc, id, stc, null);
    }

    override DtorDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto dd = new DtorDeclaration(loc, endloc, storage_class, ident);
        FuncDeclaration.syntaxCopy(dd);
        return dd;
    }

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

    override const(char)* toChars() const
    {
        return "~this";
    }

    override bool isVirtual() const
    {
        // D dtor's don't get put into the vtbl[]
        // this is a hack so that extern(C++) destructors report as virtual, which are manually added to the vtable
        return vtblIndex != -1;
    }

    override bool addPreInvariant()
    {
        return (isThis() && vthis && global.params.useInvariants == CHECKENABLE.on);
    }

    override bool addPostInvariant()
    {
        return false;
    }

    override bool overloadInsert(Dsymbol s)
    {
        return false; // cannot overload destructors
    }

    override inout(DtorDeclaration) isDtorDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) class StaticCtorDeclaration : FuncDeclaration
{
    extern (D) this(const ref Loc loc, const ref Loc endloc, StorageClass stc)
    {
        super(loc, endloc, Identifier.generateIdWithLoc("_staticCtor", loc), STC.static_ | stc, null);
    }

    extern (D) this(const ref Loc loc, const ref Loc endloc, string name, StorageClass stc)
    {
        super(loc, endloc, Identifier.generateIdWithLoc(name, loc), STC.static_ | stc, null);
    }

    override StaticCtorDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto scd = new StaticCtorDeclaration(loc, endloc, storage_class);
        FuncDeclaration.syntaxCopy(scd);
        return scd;
    }

    override final inout(AggregateDeclaration) isThis() inout @nogc nothrow pure @safe
    {
        return null;
    }

    override final bool isVirtual() const @nogc nothrow pure @safe
    {
        return false;
    }

    override final bool addPreInvariant() @nogc nothrow pure @safe
    {
        return false;
    }

    override final bool addPostInvariant() @nogc nothrow pure @safe
    {
        return false;
    }

    override final bool hasStaticCtorOrDtor() @nogc nothrow pure @safe
    {
        return true;
    }

    override final inout(StaticCtorDeclaration) isStaticCtorDeclaration() inout @nogc nothrow pure @safe
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) final class SharedStaticCtorDeclaration : StaticCtorDeclaration
{
    extern (D) this(const ref Loc loc, const ref Loc endloc, StorageClass stc)
    {
        super(loc, endloc, "_sharedStaticCtor", stc);
    }

    override SharedStaticCtorDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto scd = new SharedStaticCtorDeclaration(loc, endloc, storage_class);
        FuncDeclaration.syntaxCopy(scd);
        return scd;
    }

    override inout(SharedStaticCtorDeclaration) isSharedStaticCtorDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) class StaticDtorDeclaration : FuncDeclaration
{
    VarDeclaration vgate; // 'gate' variable

    extern (D) this(const ref Loc loc, const ref Loc endloc, StorageClass stc)
    {
        super(loc, endloc, Identifier.generateIdWithLoc("_staticDtor", loc), STC.static_ | stc, null);
    }

    extern (D) this(const ref Loc loc, const ref Loc endloc, string name, StorageClass stc)
    {
        super(loc, endloc, Identifier.generateIdWithLoc(name, loc), STC.static_ | stc, null);
    }

    override StaticDtorDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto sdd = new StaticDtorDeclaration(loc, endloc, storage_class);
        FuncDeclaration.syntaxCopy(sdd);
        return sdd;
    }

    override final inout(AggregateDeclaration) isThis() inout
    {
        return null;
    }

    override final bool isVirtual() const
    {
        return false;
    }

    override final bool hasStaticCtorOrDtor()
    {
        return true;
    }

    override final bool addPreInvariant()
    {
        return false;
    }

    override final bool addPostInvariant()
    {
        return false;
    }

    override final inout(StaticDtorDeclaration) isStaticDtorDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) final class SharedStaticDtorDeclaration : StaticDtorDeclaration
{
    extern (D) this(const ref Loc loc, const ref Loc endloc, StorageClass stc)
    {
        super(loc, endloc, "_sharedStaticDtor", stc);
    }

    override SharedStaticDtorDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto sdd = new SharedStaticDtorDeclaration(loc, endloc, storage_class);
        FuncDeclaration.syntaxCopy(sdd);
        return sdd;
    }

    override inout(SharedStaticDtorDeclaration) isSharedStaticDtorDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) final class InvariantDeclaration : FuncDeclaration
{
    extern (D) this(const ref Loc loc, const ref Loc endloc, StorageClass stc, Identifier id, Statement fbody)
    {
        super(loc, endloc, id ? id : Identifier.generateId("__invariant"), stc, null);
        this.fbody = fbody;
    }

    override InvariantDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto id = new InvariantDeclaration(loc, endloc, storage_class, null, null);
        FuncDeclaration.syntaxCopy(id);
        return id;
    }

    override bool isVirtual() const
    {
        return false;
    }

    override bool addPreInvariant()
    {
        return false;
    }

    override bool addPostInvariant()
    {
        return false;
    }

    override inout(InvariantDeclaration) isInvariantDeclaration() inout
    {
        return this;
    }

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


/***********************************************************
 */
extern (C++) final class UnitTestDeclaration : FuncDeclaration
{
    char* codedoc;      // for documented unittest

    // toObjFile() these nested functions after this one
    FuncDeclarations deferredNested;

    extern (D) this(const ref Loc loc, const ref Loc endloc, StorageClass stc, char* codedoc)
    {
        super(loc, endloc, Identifier.generateIdWithLoc("__unittest", loc), stc, null);
        this.codedoc = codedoc;
    }

    override UnitTestDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto utd = new UnitTestDeclaration(loc, endloc, storage_class, codedoc);
        FuncDeclaration.syntaxCopy(utd);
        return utd;
    }

    override inout(AggregateDeclaration) isThis() inout
    {
        return null;
    }

    override bool isVirtual() const
    {
        return false;
    }

    override bool addPreInvariant()
    {
        return false;
    }

    override bool addPostInvariant()
    {
        return false;
    }

    override inout(UnitTestDeclaration) isUnitTestDeclaration() inout
    {
        return this;
    }

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

/***********************************************************
 */
extern (C++) final class NewDeclaration : FuncDeclaration
{
    extern (D) this(const ref Loc loc, StorageClass stc)
    {
        super(loc, Loc.initial, Id.classNew, STC.static_ | stc, null);
    }

    override NewDeclaration syntaxCopy(Dsymbol s)
    {
        assert(!s);
        auto f = new NewDeclaration(loc, storage_class);
        FuncDeclaration.syntaxCopy(f);
        return f;
    }

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

    override bool isVirtual() const
    {
        return false;
    }

    override bool addPreInvariant()
    {
        return false;
    }

    override bool addPostInvariant()
    {
        return false;
    }

    override inout(NewDeclaration) isNewDeclaration() inout
    {
        return this;
    }

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