/**
 * This module contains the implementation of the C++ header generation available through
 * the command line switch -Hc.
 *
 * Copyright:   Copyright (C) 1999-2022 by The D Language Foundation, All Rights Reserved
 * Authors:     $(LINK2 https://www.digitalmars.com, Walter Bright)
 * License:     $(LINK2 https://www.boost.org/LICENSE_1_0.txt, Boost License 1.0)
 * Source:      $(LINK2 https://github.com/dlang/dmd/blob/master/src/dmd/dtohd, _dtoh.d)
 * Documentation:  https://dlang.org/phobos/dmd_dtoh.html
 * Coverage:    https://codecov.io/gh/dlang/dmd/src/master/src/dmd/dtoh.d
 */
module dmd.dtoh;

import core.stdc.stdio;
import core.stdc.string;
import core.stdc.ctype;

import dmd.astcodegen;
import dmd.astenums;
import dmd.arraytypes;
import dmd.attrib;
import dmd.dsymbol;
import dmd.errors;
import dmd.globals;
import dmd.hdrgen;
import dmd.identifier;
import dmd.root.filename;
import dmd.visitor;
import dmd.tokens;

import dmd.common.outbuffer;
import dmd.utils;

//debug = Debug_DtoH;

// Generate asserts to validate the header
//debug = Debug_DtoH_Checks;

/**
 * Generates a C++ header containing bindings for all `extern(C[++])` declarations
 * found in the supplied modules.
 *
 * Params:
 *   ms = the modules
 *
 * Notes:
 *  - the header is written to `<global.params.cxxhdrdir>/<global.params.cxxhdrfile>`
 *    or `stdout` if no explicit file was specified
 *  - bindings conform to the C++ standard defined in `global.params.cplusplus`
 *  - ignored declarations are mentioned in a comment if `global.params.doCxxHdrGeneration`
 *    is set to `CxxHeaderMode.verbose`
 */
extern(C++) void genCppHdrFiles(ref Modules ms)
{
    initialize();

    OutBuffer fwd;
    OutBuffer done;
    OutBuffer decl;

    // enable indent by spaces on buffers
    fwd.doindent = true;
    fwd.spaces = true;
    decl.doindent = true;
    decl.spaces = true;

    scope v = new ToCppBuffer(&fwd, &done, &decl);

    // Conditionally include another buffer for sanity checks
    debug (Debug_DtoH_Checks)
    {
        OutBuffer check;
        check.doindent = true;
        check.spaces = true;
        v.checkbuf = &check;
    }

    OutBuffer buf;
    buf.doindent = true;
    buf.spaces = true;

    foreach (m; ms)
        m.accept(v);

    if (global.params.doCxxHdrGeneration == CxxHeaderMode.verbose)
        buf.printf("// Automatically generated by %s Compiler v%d", global.vendor.ptr, global.versionNumber());
    else
        buf.printf("// Automatically generated by %s Compiler", global.vendor.ptr);

    buf.writenl();
    buf.writenl();
    buf.writestringln("#pragma once");
    buf.writenl();
    hashInclude(buf, "<assert.h>");
    hashInclude(buf, "<stddef.h>");
    hashInclude(buf, "<stdint.h>");
    hashInclude(buf, "<math.h>");
//    buf.writestring(buf, "#include <stdio.h>\n");
//    buf.writestring("#include <string.h>\n");

    // Emit array compatibility because extern(C++) types may have slices
    // as members (as opposed to function parameters)
    buf.writestring(`
#ifdef CUSTOM_D_ARRAY_TYPE
#define _d_dynamicArray CUSTOM_D_ARRAY_TYPE
#else
/// Represents a D [] array
template<typename T>
struct _d_dynamicArray final
{
    size_t length;
    T *ptr;

    _d_dynamicArray() : length(0), ptr(NULL) { }

    _d_dynamicArray(size_t length_in, T *ptr_in)
        : length(length_in), ptr(ptr_in) { }

    T& operator[](const size_t idx) {
        assert(idx < length);
        return ptr[idx];
    }

    const T& operator[](const size_t idx) const {
        assert(idx < length);
        return ptr[idx];
    }
};
#endif
`);

    if (v.hasReal)
    {
        hashIf(buf, "!defined(_d_real)");
        {
            hashDefine(buf, "_d_real long double");
        }
        hashEndIf(buf);
    }
    buf.writenl();
    // buf.writestringln("// fwd:");
    buf.write(&fwd);
    if (fwd.length > 0)
        buf.writenl();

    // buf.writestringln("// done:");
    buf.write(&done);

    // buf.writestringln("// decl:");
    buf.write(&decl);

    debug (Debug_DtoH_Checks)
    {
        // buf.writestringln("// check:");
        buf.writestring(`
#if OFFSETS
    template <class T>
    size_t getSlotNumber(int dummy, ...)
    {
        T c;
        va_list ap;
        va_start(ap, dummy);

        void *f = va_arg(ap, void*);
        for (size_t i = 0; ; i++)
        {
            if ( (*(void***)&c)[i] == f)
            return i;
        }
        va_end(ap);
    }

    void testOffsets()
    {
`);
        buf.write(&check);
        buf.writestring(`
    }
#endif
`);
    }

    // prevent trailing newlines
    version (Windows)
        while (buf.length >= 4 && buf[$-4..$] == "\r\n\r\n")
            buf.remove(buf.length - 2, 2);
    else
        while (buf.length >= 2 && buf[$-2..$] == "\n\n")
            buf.remove(buf.length - 1, 1);


    if (global.params.cxxhdrname is null)
    {
        // Write to stdout; assume it succeeds
        size_t n = fwrite(buf[].ptr, 1, buf.length, stdout);
        assert(n == buf.length); // keep gcc happy about return values
    }
    else
    {
        const(char)[] name = FileName.combine(global.params.cxxhdrdir, global.params.cxxhdrname);
        writeFile(Loc.initial, name, buf[]);
    }
}

private:

/****************************************************
 * Visitor that writes bindings for `extern(C[++]` declarations.
 */
extern(C++) final class ToCppBuffer : Visitor
{
    alias visit = Visitor.visit;
public:
    enum EnumKind
    {
        Int,
        Numeric,
        String,
        Enum,
        Other
    }

    /// Namespace providing the actual AST nodes
    alias AST = ASTCodegen;

    /// Visited nodes
    bool[void*] visited;

    /// Forward declared nodes (which might not be emitted yet)
    bool[void*] forwarded;

    /// Buffer for forward declarations
    OutBuffer* fwdbuf;

    /// Buffer for integrity checks
    debug (Debug_DtoH_Checks) OutBuffer* checkbuf;

    /// Buffer for declarations that must emitted before the currently
    /// visited node but can't be forward declared (see `includeSymbol`)
    OutBuffer* donebuf;

    /// Default buffer for the currently visited declaration
    OutBuffer* buf;

    /// The generated header uses `real` emitted as `_d_real`?
    bool hasReal;

    /// The generated header should contain comments for skipped declarations?
    const bool printIgnored;

    /// State specific to the current context which depends
    /// on the currently visited node and it's parents
    static struct Context
    {
        /// Default linkage in the current scope (e.g. LINK.c inside `extern(C) { ... }`)
        LINK linkage = LINK.d;

        /// Enclosing class / struct / union
        AST.AggregateDeclaration adparent;

        /// Enclosing template declaration
        AST.TemplateDeclaration tdparent;

        /// Identifier of the currently visited `VarDeclaration`
        /// (required to write variables of funtion pointers)
        Identifier ident;

        /// Original type of the currently visited declaration
        AST.Type origType;

        /// Last written visibility level applying to the current scope
        AST.Visibility.Kind currentVisibility;

        /// Currently applicable storage classes
        AST.STC storageClass;

         /// How many symbols were ignored
        int ignoredCounter;

        /// Currently visited types are required by another declaration
        /// and hence must be emitted
        bool mustEmit;

        /// Processing a type that can be forward referenced
        bool forwarding;

        /// Inside of an anonymous struct/union (AnonDeclaration)
        bool inAnonymousDecl;
    }

    /// Informations about the current context in the AST
    Context context;
    alias context this;

    this(OutBuffer* fwdbuf, OutBuffer* donebuf, OutBuffer* buf)
    {
        this.fwdbuf = fwdbuf;
        this.donebuf = donebuf;
        this.buf = buf;
        this.printIgnored = global.params.doCxxHdrGeneration == CxxHeaderMode.verbose;
    }

    /**
     * Emits `dsym` into `donebuf` s.t. it is declared before the currently
     * visited symbol that written to `buf`.
     *
     * Temporarily clears `context` to behave as if it was visited normally.
     */
    private void includeSymbol(AST.Dsymbol dsym)
    {
        debug (Debug_DtoH)
        {
            printf("[includeSymbol(AST.Dsymbol) enter] %s\n", dsym.toChars());
            scope(exit) printf("[includeSymbol(AST.Dsymbol) exit] %s\n", dsym.toChars());
        }

        auto ptr = cast(void*) dsym in visited;
        if (ptr && *ptr)
            return;

        // Temporary replacement for `buf` which is appended to `donebuf`
        OutBuffer decl;
        decl.doindent = true;
        decl.spaces = true;
        scope (exit) donebuf.write(&decl);

        auto ctxStash = this.context;
        auto bufStash = this.buf;

        this.context = Context.init;
        this.buf = &decl;
        this.mustEmit = true;

        dsym.accept(this);

        this.context = ctxStash;
        this.buf = bufStash;
    }

    /// Determines what kind of enum `type` is (see `EnumKind`)
    private EnumKind getEnumKind(AST.Type type)
    {
        if (type) switch (type.ty)
        {
            case AST.Tint32:
                return EnumKind.Int;
            case AST.Tbool,
                AST.Tchar, AST.Twchar, AST.Tdchar,
                AST.Tint8, AST.Tuns8,
                AST.Tint16, AST.Tuns16,
                AST.Tuns32,
                AST.Tint64, AST.Tuns64:
                return EnumKind.Numeric;
            case AST.Tarray:
                if (type.isString())
                    return EnumKind.String;
                break;
            case AST.Tenum:
                return EnumKind.Enum;
            default:
                break;
        }
        return EnumKind.Other;
    }

    /// Determines the type used to represent `type` in C++.
    /// Returns: `const [w,d]char*` for `[w,d]string` or `type`
    private AST.Type determineEnumType(AST.Type type)
    {
        if (auto arr = type.isTypeDArray())
        {
            switch (arr.next.ty)
            {
                case AST.Tchar:  return AST.Type.tchar.constOf.pointerTo;
                case AST.Twchar: return AST.Type.twchar.constOf.pointerTo;
                case AST.Tdchar: return AST.Type.tdchar.constOf.pointerTo;
                default: break;
            }
        }
        return type;
    }

    /// Writes a final `;` and insert an empty line outside of aggregates
    private void writeDeclEnd()
    {
        buf.writestringln(";");

        if (!adparent)
            buf.writenl();
    }

    /// Writes the corresponding access specifier if necessary
    private void writeProtection(const AST.Visibility.Kind kind)
    {
        // Don't write visibility for global declarations
        if (!adparent || inAnonymousDecl)
            return;

        string token;

        switch(kind) with(AST.Visibility.Kind)
        {
            case none, private_:
                if (this.currentVisibility == AST.Visibility.Kind.private_)
                    return;
                this.currentVisibility = AST.Visibility.Kind.private_;
                token = "private:";
                break;

            case package_, protected_:
                if (this.currentVisibility == AST.Visibility.Kind.protected_)
                    return;
                this.currentVisibility = AST.Visibility.Kind.protected_;
                token = "protected:";
                break;

            case undefined, public_, export_:
                if (this.currentVisibility == AST.Visibility.Kind.public_)
                    return;
                this.currentVisibility = AST.Visibility.Kind.public_;
                token = "public:";
                break;

            default:
                printf("Unexpected visibility: %d!\n", kind);
                assert(0);
        }

        buf.level--;
        buf.writestringln(token);
        buf.level++;
    }

    /**
     * Writes an identifier into `buf` and checks for reserved identifiers. The
     * parameter `canFix` determines how this function handles C++ keywords:
     *
     * `false` => Raise a warning and print the identifier as-is
     * `true`  => Append an underscore to the identifier
     *
     * Params:
     *   s        = the symbol denoting the identifier
     *   canFixup = whether the identifier may be changed without affecting
     *              binary compatibility
     */
    private void writeIdentifier(const AST.Dsymbol s, const bool canFix = false)
    {
        if (const mn = getMangleOverride(s))
            return buf.writestring(mn);

        writeIdentifier(s.ident, s.loc, s.kind(), canFix);
    }

    /** Overload of `writeIdentifier` used for all AST nodes not descending from Dsymbol **/
    private void writeIdentifier(const Identifier ident, const Loc loc, const char* kind, const bool canFix = false)
    {
        bool needsFix;

        void warnCxxCompat(const(char)* reason)
        {
            if (canFix)
            {
                needsFix = true;
                return;
            }

            __gshared bool warned = false;
            warning(loc, "%s `%s` is a %s", kind, ident.toChars(), reason);

            if (!warned)
            {
                warningSupplemental(loc, "The generated C++ header will contain " ~
                                    "identifiers that are keywords in C++");
                warned = true;
            }
        }

        if (global.params.warnings != DiagnosticReporting.off || canFix)
        {
            // Warn about identifiers that are keywords in C++.
            if (auto kc = keywordClass(ident))
                warnCxxCompat(kc);
        }
        buf.writestring(ident.toString());
        if (needsFix)
            buf.writeByte('_');
    }

    /// Checks whether `t` is a type that can be exported to C++
    private bool isSupportedType(AST.Type t)
    {
        if (!t)
        {
            assert(tdparent);
            return true;
        }

        switch (t.ty)
        {
            // Nested types
            case AST.Tarray:
            case AST.Tsarray:
            case AST.Tpointer:
            case AST.Treference:
            case AST.Tdelegate:
                return isSupportedType((cast(AST.TypeNext) t).next);

            // Function pointers
            case AST.Tfunction:
            {
                auto tf = cast(AST.TypeFunction) t;
                if (!isSupportedType(tf.next))
                    return false;
                foreach (_, param; tf.parameterList)
                {
                    if (!isSupportedType(param.type))
                        return false;
                }
                return true;
            }

            // Noreturn has a different mangling
            case AST.Tnoreturn:

            // _Imaginary is C only.
            case AST.Timaginary32:
            case AST.Timaginary64:
            case AST.Timaginary80:
                return false;
            default:
                return true;
        }
    }

    override void visit(AST.Dsymbol s)
    {
        debug (Debug_DtoH)
        {
            mixin(traceVisit!s);
            import dmd.asttypename;
            printf("[AST.Dsymbol enter] %s\n", s.astTypeName().ptr);
        }
    }

    override void visit(AST.Import i)
    {
        debug (Debug_DtoH) mixin(traceVisit!i);

        /// Writes `using <alias_> = <sym.ident>` into `buf`
        const(char*) writeImport(AST.Dsymbol sym, const Identifier alias_)
        {
            /// `using` was introduced in C++ 11 and only works for types...
            if (global.params.cplusplus < CppStdRevision.cpp11)
                return "requires C++11";

            if (auto ad = sym.isAliasDeclaration())
            {
                sym = ad.toAlias();
                ad = sym.isAliasDeclaration();

                // Might be an alias to a basic type
                if (ad && !ad.aliassym && ad.type)
                    goto Emit;
            }

            // Restricted to types and other aliases
            if (!sym.isScopeDsymbol() && !sym.isAggregateDeclaration())
                return "only supports types";

            // Write `using <alias_> = `<sym>`
            Emit:
            buf.writestring("using ");
            writeIdentifier(alias_, i.loc, "renamed import");
            buf.writestring(" = ");
            // Start at module scope to avoid collisions with local symbols
            if (this.context.adparent)
                buf.writestring("::");
            buf.writestring(sym.ident.toString());
            writeDeclEnd();
            return null;
        }

        // Only missing without semantic analysis
        // FIXME: Templates need work due to missing parent & imported module
        if (!i.parent)
        {
            assert(tdparent);
            ignored("`%s` because it's inside of a template declaration", i.toChars());
            return;
        }

        // Non-public imports don't create new symbols, include as needed
        if (i.visibility.kind < AST.Visibility.Kind.public_)
            return;

        // Symbols from static imports should be emitted inline
        if (i.isstatic)
            return;

        const isLocal = !i.parent.isModule();

        // Need module for symbol lookup
        assert(i.mod);

        // Emit an alias for each public module member
        if (isLocal && i.names.length == 0)
        {
            assert(i.mod.symtab);

            // Sort alphabetically s.t. slight changes in semantic don't cause
            // massive changes in the order of declarations
            AST.Dsymbols entries;
            entries.reserve(i.mod.symtab.length);

            foreach (entry; i.mod.symtab.tab.asRange)
            {
                // Skip anonymous / invisible members
                import dmd.access : symbolIsVisible;
                if (!entry.key.isAnonymous() && symbolIsVisible(i, entry.value))
                    entries.push(entry.value);
            }

            // Seperate function because of a spurious dual-context deprecation
            static int compare(const AST.Dsymbol* a, const AST.Dsymbol* b)
            {
                return strcmp(a.ident.toChars(), b.ident.toChars());
            }
            entries.sort!compare();

            foreach (sym; entries)
            {
                includeSymbol(sym);
                if (auto err = writeImport(sym, sym.ident))
                    ignored("public import for `%s` because `using` %s", sym.ident.toChars(), err);
            }
            return;
        }

        // Include all public imports and emit using declarations for each alias
        foreach (const idx, name; i.names)
        {
            // Search the imported symbol
            auto sym = i.mod.search(Loc.initial, name);
            assert(sym); // Missing imports should error during semantic

            includeSymbol(sym);

            // Detect the assigned name for renamed import
            auto alias_ = i.aliases[idx];
            if (!alias_)
                continue;

            if (auto err = writeImport(sym, alias_))
                ignored("renamed import `%s = %s` because `using` %s", alias_.toChars(), name.toChars(), err);
        }
    }

    override void visit(AST.AttribDeclaration pd)
    {
        debug (Debug_DtoH) mixin(traceVisit!pd);

        Dsymbols* decl = pd.include(null);
        if (!decl)
            return;

        foreach (s; *decl)
        {
            if (adparent || s.visible().kind >= AST.Visibility.Kind.public_)
                s.accept(this);
        }
    }

    override void visit(AST.StorageClassDeclaration scd)
    {
        debug (Debug_DtoH) mixin(traceVisit!scd);

        const stcStash = this.storageClass;
        this.storageClass |= scd.stc;
        visit(cast(AST.AttribDeclaration) scd);
        this.storageClass = stcStash;
    }

    override void visit(AST.LinkDeclaration ld)
    {
        debug (Debug_DtoH) mixin(traceVisit!ld);

        auto save = linkage;
        linkage = ld.linkage;
        visit(cast(AST.AttribDeclaration)ld);
        linkage = save;
    }

    override void visit(AST.CPPMangleDeclaration md)
    {
        debug (Debug_DtoH) mixin(traceVisit!md);

        const oldLinkage = this.linkage;
        this.linkage = LINK.cpp;
        visit(cast(AST.AttribDeclaration) md);
        this.linkage = oldLinkage;
    }

    override void visit(AST.Module m)
    {
        debug (Debug_DtoH) mixin(traceVisit!m);

        foreach (s; *m.members)
        {
            if (s.visible().kind < AST.Visibility.Kind.public_)
                continue;
            s.accept(this);
        }
    }

    override void visit(AST.FuncDeclaration fd)
    {
        debug (Debug_DtoH) mixin(traceVisit!fd);

        if (cast(void*)fd in visited)
            return;
        // printf("FuncDeclaration %s %s\n", fd.toPrettyChars(), fd.type.toChars());
        visited[cast(void*)fd] = true;

        // silently ignore non-user-defined destructors
        if (fd.isGenerated && fd.isDtorDeclaration())
            return;

        // Note that tf might be null for templated (member) functions
        auto tf = cast(AST.TypeFunction)fd.type;
        if ((tf && (tf.linkage != LINK.c || adparent) && tf.linkage != LINK.cpp) || (!tf && fd.isPostBlitDeclaration()))
        {
            ignored("function %s because of linkage", fd.toPrettyChars());
            return checkFunctionNeedsPlaceholder(fd);
        }
        if (fd.mangleOverride && tf && tf.linkage != LINK.c)
        {
            ignored("function %s because C++ doesn't support explicit mangling", fd.toPrettyChars());
            return checkFunctionNeedsPlaceholder(fd);
        }
        if (!adparent && !fd.fbody)
        {
            ignored("function %s because it is extern", fd.toPrettyChars());
            return;
        }
        if (fd.visibility.kind == AST.Visibility.Kind.none || fd.visibility.kind == AST.Visibility.Kind.private_)
        {
            ignored("function %s because it is private", fd.toPrettyChars());
            return;
        }
        if (tf && !isSupportedType(tf.next))
        {
            ignored("function %s because its return type cannot be mapped to C++", fd.toPrettyChars());
            return checkFunctionNeedsPlaceholder(fd);
        }
        if (tf) foreach (i, fparam; tf.parameterList)
        {
            if (!isSupportedType(fparam.type))
            {
                ignored("function %s because one of its parameters has type `%s` which cannot be mapped to C++",
                        fd.toPrettyChars(), fparam.type.toChars());
                return checkFunctionNeedsPlaceholder(fd);
            }
        }

        writeProtection(fd.visibility.kind);

        if (tf && tf.linkage == LINK.c)
            buf.writestring("extern \"C\" ");
        else if (!adparent)
            buf.writestring("extern ");
        if (adparent && fd.isStatic())
            buf.writestring("static ");
        else if (adparent && (
            // Virtual functions in non-templated classes
            (fd.vtblIndex != -1 && !fd.isOverride()) ||

            // Virtual functions in templated classes (fd.vtblIndex still -1)
            (tdparent && adparent.isClassDeclaration() && !(this.storageClass & AST.STC.final_ || fd.isFinal))))
                buf.writestring("virtual ");

        debug (Debug_DtoH_Checks)
        if (adparent && !tdparent)
        {
            auto s = adparent.search(Loc.initial, fd.ident);
            auto cd = adparent.isClassDeclaration();

            if (!(adparent.storage_class & AST.STC.abstract_) &&
                !(cd && cd.isAbstract()) &&
                s is fd && !fd.overnext)
            {
                const cn = adparent.ident.toChars();
                const fn = fd.ident.toChars();
                const vi = fd.vtblIndex;

                checkbuf.printf("assert(getSlotNumber <%s>(0, &%s::%s) == %d);",
                                                       cn,     cn, fn,    vi);
                checkbuf.writenl();
           }
        }

        if (adparent && fd.isDisabled && global.params.cplusplus < CppStdRevision.cpp11)
            writeProtection(AST.Visibility.Kind.private_);
        funcToBuffer(tf, fd);
        // FIXME: How to determine if fd is const without tf?
        if (adparent && tf && (tf.isConst() || tf.isImmutable()))
        {
            bool fdOverridesAreConst = true;
            foreach (fdv; fd.foverrides)
            {
                auto tfv = cast(AST.TypeFunction)fdv.type;
                if (!tfv.isConst() && !tfv.isImmutable())
                {
                    fdOverridesAreConst = false;
                    break;
                }
            }

            buf.writestring(fdOverridesAreConst ? " const" : " /* const */");
        }
        if (adparent && fd.isAbstract())
            buf.writestring(" = 0");
        if (adparent && fd.isDisabled && global.params.cplusplus >= CppStdRevision.cpp11)
            buf.writestring(" = delete");
        buf.writestringln(";");
        if (adparent && fd.isDisabled && global.params.cplusplus < CppStdRevision.cpp11)
            writeProtection(AST.Visibility.Kind.public_);

        if (!adparent)
            buf.writenl();

    }

    /++
     + Checks whether `fd` is a function that requires a dummy declaration
     + instead of simply emitting the declaration (because it would cause
     + ABI / behaviour issues). This includes:
     +
     + - virtual functions to ensure proper vtable layout
     + - destructors that would break RAII
     +/
    private void checkFunctionNeedsPlaceholder(AST.FuncDeclaration fd)
    {
        // Omit redundant declarations - the slot was already
        // reserved in the base class
        if (fd.isVirtual() && fd.isIntroducing())
        {
            // Hide placeholders because they are not ABI compatible
            writeProtection(AST.Visibility.Kind.private_);

            __gshared int counter; // Ensure unique names in all cases
            buf.printf("virtual void __vtable_slot_%u();", counter++);
            buf.writenl();
        }
        else if (fd.isDtorDeclaration())
        {
            // Create inaccessible dtor to prevent code from keeping instances that
            // need to be destroyed on the C++ side (but cannot call the dtor)
            writeProtection(AST.Visibility.Kind.private_);
            buf.writeByte('~');
            buf.writestring(adparent.ident.toString());
            buf.writestringln("();");
        }
    }

    override void visit(AST.UnitTestDeclaration utd)
    {
        debug (Debug_DtoH) mixin(traceVisit!utd);
    }

    override void visit(AST.VarDeclaration vd)
    {
        debug (Debug_DtoH) mixin(traceVisit!vd);

        if (!shouldEmitAndMarkVisited(vd))
            return;

        // Tuple field are expanded into multiple VarDeclarations
        // (we'll visit them later)
        if (vd.type && vd.type.isTypeTuple())
            return;

        if (vd.originalType && vd.type == AST.Type.tsize_t)
            origType = vd.originalType;
        scope(exit) origType = null;

        if (!vd.alignment.isDefault() && !vd.alignment.isUnknown())
        {
            buf.printf("// Ignoring var %s alignment %d", vd.toChars(), vd.alignment.get());
            buf.writenl();
        }

        // Determine the variable type which might be missing inside of
        // template declarations. Infer the type from the initializer then
        AST.Type type = vd.type;
        if (!type)
        {
            assert(tdparent);

            // Just a precaution, implicit type without initializer should be rejected
            if (!vd._init)
                return;

            if (auto ei = vd._init.isExpInitializer())
                type = ei.exp.type;

            // Can happen if the expression needs further semantic
            if (!type)
            {
                ignored("%s because the type could not be determined", vd.toPrettyChars());
                return;
            }

            // Apply const/immutable to the inferred type
            if (vd.storage_class & (AST.STC.const_ | AST.STC.immutable_))
                type = type.constOf();
        }

        if (vd.storage_class & AST.STC.manifest)
        {
            EnumKind kind = getEnumKind(type);

            if (vd.visibility.kind == AST.Visibility.Kind.none || vd.visibility.kind == AST.Visibility.Kind.private_) {
                ignored("enum `%s` because it is `%s`.", vd.toPrettyChars(), AST.visibilityToChars(vd.visibility.kind));
                return;
            }

            writeProtection(vd.visibility.kind);

            final switch (kind)
            {
                case EnumKind.Int, EnumKind.Numeric:
                    // 'enum : type' is only available from C++-11 onwards.
                    if (global.params.cplusplus < CppStdRevision.cpp11)
                        goto case;
                    buf.writestring("enum : ");
                    determineEnumType(type).accept(this);
                    buf.writestring(" { ");
                    writeIdentifier(vd, true);
                    buf.writestring(" = ");
                    auto ie = AST.initializerToExpression(vd._init).isIntegerExp();
                    visitInteger(ie.toInteger(), type);
                    buf.writestring(" };");
                    break;

                case EnumKind.String, EnumKind.Enum:
                    buf.writestring("static ");
                    auto target = determineEnumType(type);
                    target.accept(this);
                    buf.writestring(" const ");
                    writeIdentifier(vd, true);
                    buf.writestring(" = ");
                    auto e = AST.initializerToExpression(vd._init);
                    printExpressionFor(target, e);
                    buf.writestring(";");
                    break;

                case EnumKind.Other:
                    ignored("enum `%s` because type `%s` is currently not supported for enum constants.", vd.toPrettyChars(), type.toChars());
                    return;
            }
            buf.writenl();
            buf.writenl();
            return;
        }

        if (vd.storage_class & (AST.STC.static_ | AST.STC.extern_ | AST.STC.gshared) ||
        vd.parent && vd.parent.isModule())
        {
            const vdLinkage = vd.resolvedLinkage();
            if (vdLinkage != LINK.c && vdLinkage != LINK.cpp && !(tdparent && (this.linkage == LINK.c || this.linkage == LINK.cpp)))
            {
                ignored("variable %s because of linkage", vd.toPrettyChars());
                return;
            }
            if (vd.mangleOverride && vdLinkage != LINK.c)
            {
                ignored("variable %s because C++ doesn't support explicit mangling", vd.toPrettyChars());
                return;
            }
            if (!isSupportedType(type))
            {
                ignored("variable %s because its type cannot be mapped to C++", vd.toPrettyChars());
                return;
            }
            if (auto kc = keywordClass(vd.ident))
            {
                ignored("variable %s because its name is a %s", vd.toPrettyChars(), kc);
                return;
            }
            writeProtection(vd.visibility.kind);
            if (vdLinkage == LINK.c)
                buf.writestring("extern \"C\" ");
            else if (!adparent)
                buf.writestring("extern ");
            if (adparent)
                buf.writestring("static ");
            typeToBuffer(type, vd);
            writeDeclEnd();
            return;
        }

        if (adparent)
        {
            writeProtection(vd.visibility.kind);
            typeToBuffer(type, vd, true);
            buf.writestringln(";");

            debug (Debug_DtoH_Checks)
            {
                checkbuf.level++;
                const pn = adparent.ident.toChars();
                const vn = vd.ident.toChars();
                const vo = vd.offset;
                checkbuf.printf("assert(offsetof(%s, %s) == %d);",
                                                pn, vn,    vo);
                checkbuf.writenl();
                checkbuf.level--;
            }
            return;
        }

        visit(cast(AST.Dsymbol)vd);
    }

    override void visit(AST.TypeInfoDeclaration tid)
    {
        debug (Debug_DtoH) mixin(traceVisit!tid);
    }

    override void visit(AST.AliasDeclaration ad)
    {
        debug (Debug_DtoH) mixin(traceVisit!ad);

        if (!shouldEmitAndMarkVisited(ad))
            return;

        writeProtection(ad.visibility.kind);

        if (auto t = ad.type)
        {
            if (t.ty == AST.Tdelegate || t.ty == AST.Tident)
            {
                visit(cast(AST.Dsymbol)ad);
                return;
            }

            // for function pointers we need to original type
            if (ad.originalType && ad.type.ty == AST.Tpointer &&
                (cast(AST.TypePointer)t).nextOf.ty == AST.Tfunction)
            {
                origType = ad.originalType;
            }
            scope(exit) origType = null;

            buf.writestring("typedef ");
            typeToBuffer(origType !is null ? origType : t, ad);
            writeDeclEnd();
            return;
        }
        if (!ad.aliassym)
        {
            assert(0);
        }
        if (auto ti = ad.aliassym.isTemplateInstance())
        {
            visitTi(ti);
            return;
        }
        if (auto sd = ad.aliassym.isStructDeclaration())
        {
            buf.writestring("typedef ");
            sd.type.accept(this);
            buf.writestring(" ");
            writeIdentifier(ad);
            writeDeclEnd();
            return;
        }
        else if (auto td = ad.aliassym.isTemplateDeclaration())
        {
            if (global.params.cplusplus < CppStdRevision.cpp11)
            {
                ignored("%s because `using` declarations require C++ 11", ad.toPrettyChars());
                return;
            }

            printTemplateParams(td);
            buf.writestring("using ");
            writeIdentifier(ad);
            buf.writestring(" = ");
            writeFullName(td);
            buf.writeByte('<');

            foreach (const idx, const p; *td.parameters)
            {
                if (idx)
                    buf.writestring(", ");
                writeIdentifier(p.ident, p.loc, "parameter", true);
            }
            buf.writestringln(">;");
            return;
        }

        auto fd = ad.aliassym.isFuncDeclaration();

        if (fd && (fd.isGenerated() || fd.isDtorDeclaration()))
        {
            // Ignore. It's taken care of while visiting FuncDeclaration
            return;
        }

        // Recognize member function aliases, e.g. alias visit = Parent.visit;
        if (adparent && fd)
        {
            auto pd = fd.isMember();
            if (!pd)
            {
                ignored("%s because free functions cannot be aliased in C++", ad.toPrettyChars());
            }
            else if (global.params.cplusplus < CppStdRevision.cpp11)
            {
                ignored("%s because `using` declarations require C++ 11", ad.toPrettyChars());
            }
            else if (ad.ident != fd.ident)
            {
                ignored("%s because `using` cannot rename functions in aggregates", ad.toPrettyChars());
            }
            else if (fd.toAliasFunc().parent.isTemplateMixin())
            {
                // Member's of template mixins are directly emitted into the aggregate
            }
            else
            {
                buf.writestring("using ");

                // Print prefix of the base class if this function originates from a superclass
                // because alias might be resolved through multiple classes, e.g.
                // e.g. for alias visit = typeof(super).visit in the visitors
                if (!fd.isIntroducing())
                    printPrefix(ad.toParent().isClassDeclaration().baseClass);
                else
                    printPrefix(pd);

                buf.writestring(fd.ident.toChars());
                buf.writestringln(";");
            }
            return;
        }

        ignored("%s %s", ad.aliassym.kind(), ad.aliassym.toPrettyChars());
    }

    override void visit(AST.Nspace ns)
    {
        debug (Debug_DtoH) mixin(traceVisit!ns);
        handleNspace(ns, ns.members);
    }

    override void visit(AST.CPPNamespaceDeclaration ns)
    {
        debug (Debug_DtoH) mixin(traceVisit!ns);
        handleNspace(ns, ns.decl);
    }

    /// Writes the namespace declaration and visits all members
    private void handleNspace(AST.Dsymbol namespace, Dsymbols* members)
    {
        buf.writestring("namespace ");
        writeIdentifier(namespace);
        buf.writenl();
        buf.writestring("{");
        buf.writenl();
        buf.level++;
        foreach(decl;(*members))
        {
            decl.accept(this);
        }
        buf.level--;
        buf.writestring("}");
        buf.writenl();
    }

    override void visit(AST.AnonDeclaration ad)
    {
        debug (Debug_DtoH) mixin(traceVisit!ad);

        const anonStash = inAnonymousDecl;
        inAnonymousDecl = true;
        scope (exit) inAnonymousDecl = anonStash;

        buf.writestringln(ad.isunion ? "union" : "struct");
        buf.writestringln("{");
        buf.level++;
        foreach (s; *ad.decl)
        {
            s.accept(this);
        }
        buf.level--;
        buf.writestringln("};");
    }

    private bool memberField(AST.VarDeclaration vd)
    {
        if (!vd.type || !vd.type.deco || !vd.ident)
            return false;
        if (!vd.isField())
            return false;
        if (vd.type.ty == AST.Tfunction)
            return false;
        if (vd.type.ty == AST.Tsarray)
            return false;
        return true;
    }

    override void visit(AST.StructDeclaration sd)
    {
        debug (Debug_DtoH) mixin(traceVisit!sd);

        if (!shouldEmitAndMarkVisited(sd))
            return;

        const ignoredStash = this.ignoredCounter;
        scope (exit) this.ignoredCounter = ignoredStash;

        pushAlignToBuffer(sd.alignment);

        writeProtection(sd.visibility.kind);

        const structAsClass = sd.cppmangle == CPPMANGLE.asClass;
        if (sd.isUnionDeclaration())
            buf.writestring("union ");
        else
            buf.writestring(structAsClass ? "class " : "struct ");

        writeIdentifier(sd);
        if (!sd.members)
        {
            buf.writestringln(";");
            buf.writenl();
            return;
        }

        // D structs are always final
        if (!sd.isUnionDeclaration())
            buf.writestring(" final");

        buf.writenl();
        buf.writestring("{");

        const protStash = this.currentVisibility;
        this.currentVisibility = structAsClass ? AST.Visibility.Kind.private_ : AST.Visibility.Kind.public_;
        scope (exit) this.currentVisibility = protStash;

        buf.level++;
        buf.writenl();
        auto save = adparent;
        adparent = sd;

        foreach (m; *sd.members)
        {
            m.accept(this);
        }
        // Generate default ctor
        if (!sd.noDefaultCtor && !sd.isUnionDeclaration())
        {
            writeProtection(AST.Visibility.Kind.public_);
            buf.printf("%s()", sd.ident.toChars());
            size_t varCount;
            bool first = true;
            buf.level++;
            foreach (m; *sd.members)
            {
                if (auto vd = m.isVarDeclaration())
                {
                    if (!memberField(vd))
                        continue;
                    varCount++;

                    if (!vd._init && !vd.type.isTypeBasic() && !vd.type.isTypePointer && !vd.type.isTypeStruct &&
                        !vd.type.isTypeClass && !vd.type.isTypeDArray && !vd.type.isTypeSArray)
                    {
                        continue;
                    }
                    if (vd._init && vd._init.isVoidInitializer())
                        continue;

                    if (first)
                    {
                        buf.writestringln(" :");
                        first = false;
                    }
                    else
                    {
                        buf.writestringln(",");
                    }
                    writeIdentifier(vd, true);
                    buf.writeByte('(');

                    if (vd._init)
                    {
                        auto e = AST.initializerToExpression(vd._init);
                        printExpressionFor(vd.type, e, true);
                    }
                    buf.printf(")");
                }
            }
            buf.level--;
            buf.writenl();
            buf.writestringln("{");
            buf.writestringln("}");
            auto ctor = sd.ctor ? sd.ctor.isFuncDeclaration() : null;
            if (varCount && (!ctor || ctor.storage_class & AST.STC.disable))
            {
                buf.printf("%s(", sd.ident.toChars());
                first = true;
                foreach (m; *sd.members)
                {
                    if (auto vd = m.isVarDeclaration())
                    {
                        if (!memberField(vd))
                            continue;
                        if (!first)
                            buf.writestring(", ");
                        assert(vd.type);
                        assert(vd.ident);
                        typeToBuffer(vd.type, vd, true);
                        // Don't print default value for first parameter to not clash
                        // with the default ctor defined above
                        if (!first)
                        {
                            buf.writestring(" = ");
                            printExpressionFor(vd.type, findDefaultInitializer(vd));
                        }
                        first = false;
                    }
                }
                buf.writestring(") :");
                buf.level++;
                buf.writenl();

                first = true;
                foreach (m; *sd.members)
                {
                    if (auto vd = m.isVarDeclaration())
                    {
                        if (!memberField(vd))
                            continue;

                        if (first)
                            first = false;
                        else
                            buf.writestringln(",");

                        writeIdentifier(vd, true);
                        buf.writeByte('(');
                        writeIdentifier(vd, true);
                        buf.writeByte(')');
                    }
                }
                buf.writenl();
                buf.writestringln("{}");
                buf.level--;
            }
        }

        buf.level--;
        adparent = save;
        buf.writestringln("};");

        popAlignToBuffer(sd.alignment);
        buf.writenl();

        // Workaround because size triggers a forward-reference error
        // for struct templates (the size is undetermined even if the
        // size doesn't depend on the parameters)
        debug (Debug_DtoH_Checks)
        if (!tdparent)
        {
            checkbuf.level++;
            const sn = sd.ident.toChars();
            const sz = sd.size(Loc.initial);
            checkbuf.printf("assert(sizeof(%s) == %llu);", sn, sz);
            checkbuf.writenl();
            checkbuf.level--;
        }
    }

    /// Starts a custom alignment section using `#pragma pack` if
    /// `alignment` specifies a custom alignment
    private void pushAlignToBuffer(structalign_t alignment)
    {
        // DMD ensures alignment is a power of two
        //assert(alignment > 0 && ((alignment & (alignment - 1)) == 0),
        //       "Invalid alignment size");

        // When no alignment is specified, `uint.max` is the default
        // FIXME: alignment is 0 for structs templated members
        if (alignment.isDefault() || (tdparent && alignment.isUnknown()))
        {
            return;
        }

        buf.printf("#pragma pack(push, %d)", alignment.get());
        buf.writenl();
    }

    /// Ends a custom alignment section using `#pragma pack` if
    /// `alignment` specifies a custom alignment
    private void popAlignToBuffer(structalign_t alignment)
    {
        if (alignment.isDefault() || (tdparent && alignment.isUnknown()))
            return;

        buf.writestringln("#pragma pack(pop)");
    }

    override void visit(AST.ClassDeclaration cd)
    {
        debug (Debug_DtoH) mixin(traceVisit!cd);

        if (cd.baseClass && shouldEmit(cd))
            includeSymbol(cd.baseClass);

        if (!shouldEmitAndMarkVisited(cd))
            return;

        writeProtection(cd.visibility.kind);

        const classAsStruct = cd.cppmangle == CPPMANGLE.asStruct;
        buf.writestring(classAsStruct ? "struct " : "class ");
        writeIdentifier(cd);

        if (cd.storage_class & AST.STC.final_ || (tdparent && this.storageClass & AST.STC.final_))
            buf.writestring(" final");

        assert(cd.baseclasses);

        foreach (i, base; *cd.baseclasses)
        {
            buf.writestring(i == 0 ? " : public " : ", public ");

            // Base classes/interfaces might depend on template parameters,
            // e.g. class A(T) : B!T { ... }
            if (base.sym is null)
            {
                base.type.accept(this);
            }
            else
            {
                writeFullName(base.sym);
            }
        }

        if (!cd.members)
        {
            buf.writestring(";");
            buf.writenl();
            buf.writenl();
            return;
        }

        buf.writenl();
        buf.writestringln("{");

        const protStash = this.currentVisibility;
        this.currentVisibility = classAsStruct ? AST.Visibility.Kind.public_ : AST.Visibility.Kind.private_;
        scope (exit) this.currentVisibility = protStash;

        auto save = adparent;
        adparent = cd;
        buf.level++;
        foreach (m; *cd.members)
        {
            m.accept(this);
        }
        buf.level--;
        adparent = save;

        buf.writestringln("};");
        buf.writenl();
    }

    override void visit(AST.EnumDeclaration ed)
    {
        debug (Debug_DtoH) mixin(traceVisit!ed);

        if (!shouldEmitAndMarkVisited(ed))
            return;

        if (ed.isSpecial())
        {
            //ignored("%s because it is a special C++ type", ed.toPrettyChars());
            return;
        }

        // we need to know a bunch of stuff about the enum...
        bool isAnonymous = ed.ident is null;
        const isOpaque = !ed.members;
        AST.Type type = ed.memtype;
        if (!type && !isOpaque)
        {
            // check all keys have matching type
            foreach (_m; *ed.members)
            {
                auto m = _m.isEnumMember();
                if (!type)
                    type = m.type;
                else if (m.type !is type)
                {
                    type = null;
                    break;
                }
            }
        }
        EnumKind kind = getEnumKind(type);

        if (isOpaque)
        {
            // Opaque enums were introduced in C++ 11 (workaround?)
            if (global.params.cplusplus < CppStdRevision.cpp11)
            {
                ignored("%s because opaque enums require C++ 11", ed.toPrettyChars());
                return;
            }
            // Opaque enum defaults to int but the type might not be set
            else if (!type)
            {
                kind = EnumKind.Int;
            }
            // Cannot apply namespace workaround for non-integral types
            else if (kind != EnumKind.Int && kind != EnumKind.Numeric)
            {
                ignored("enum %s because of its base type", ed.toPrettyChars());
                return;
            }
        }

        // determine if this is an enum, or just a group of manifest constants
        bool manifestConstants = !isOpaque && (!type || (isAnonymous && kind == EnumKind.Other));
        assert(!manifestConstants || isAnonymous);

        writeProtection(ed.visibility.kind);

        // write the enum header
        if (!manifestConstants)
        {
            if (kind == EnumKind.Int || kind == EnumKind.Numeric)
            {
                buf.writestring("enum");
                // D enums are strong enums, but there exists only a direct mapping
                // with 'enum class' from C++-11 onwards.
                if (global.params.cplusplus >= CppStdRevision.cpp11)
                {
                    if (!isAnonymous)
                    {
                        buf.writestring(" class ");
                        writeIdentifier(ed);
                    }
                    if (kind == EnumKind.Numeric)
                    {
                        buf.writestring(" : ");
                        determineEnumType(type).accept(this);
                    }
                }
                else if (!isAnonymous)
                {
                    buf.writeByte(' ');
                    writeIdentifier(ed);
                }
            }
            else
            {
                buf.writestring("namespace");
                if(!isAnonymous)
                {
                    buf.writeByte(' ');
                    writeIdentifier(ed);
                }
            }
            // Opaque enums have no members, hence skip the body
            if (isOpaque)
            {
                buf.writestringln(";");
                return;
            }
            else
            {
                buf.writenl();
                buf.writestringln("{");
            }
        }

        // emit constant for each member
        if (!manifestConstants)
            buf.level++;

        foreach (_m; *ed.members)
        {
            auto m = _m.isEnumMember();
            AST.Type memberType = type ? type : m.type;
            const EnumKind memberKind = type ? kind : getEnumKind(memberType);

            if (!manifestConstants && (kind == EnumKind.Int || kind == EnumKind.Numeric))
            {
                // C++-98 compatible enums must use the typename as a prefix to avoid
                // collisions with other identifiers in scope.  For consistency with D,
                // the enum member `Type.member` is emitted as `Type_member` in C++-98.
                if (!isAnonymous && global.params.cplusplus < CppStdRevision.cpp11)
                {
                    writeIdentifier(ed);
                    buf.writeByte('_');
                }
                writeIdentifier(m, true);
                buf.writestring(" = ");

                auto ie = cast(AST.IntegerExp)m.value;
                visitInteger(ie.toInteger(), memberType);
                buf.writestring(",");
            }
            else if (global.params.cplusplus >= CppStdRevision.cpp11 &&
                     manifestConstants && (memberKind == EnumKind.Int || memberKind == EnumKind.Numeric))
            {
                buf.writestring("enum : ");
                determineEnumType(memberType).accept(this);
                buf.writestring(" { ");
                writeIdentifier(m, true);
                buf.writestring(" = ");

                auto ie = cast(AST.IntegerExp)m.value;
                visitInteger(ie.toInteger(), memberType);
                buf.writestring(" };");
            }
            else
            {
                buf.writestring("static ");
                auto target = determineEnumType(memberType);
                target.accept(this);
                buf.writestring(" const ");
                writeIdentifier(m, true);
                buf.writestring(" = ");
                printExpressionFor(target, m.origValue);
                buf.writestring(";");
            }
            buf.writenl();
        }

        if (!manifestConstants)
            buf.level--;
        // write the enum tail
        if (!manifestConstants)
            buf.writestring("};");
        buf.writenl();
        buf.writenl();
    }

    override void visit(AST.EnumMember em)
    {
        assert(em.ed);

        // Members of anonymous members are reachable without referencing the
        // EnumDeclaration, e.g. public import foo : someEnumMember;
        if (em.ed.isAnonymous())
        {
            visit(em.ed);
            return;
        }

        assert(false, "This node type should be handled in the EnumDeclaration");
    }

    /**
     * Prints a member/parameter/variable declaration into `buf`.
     *
     * Params:
     *   t        = the type (used if `this.origType` is null)
     *   s        = the symbol denoting the identifier
     *   canFixup = whether the identifier may be changed without affecting
     *              binary compatibility (forwarded to `writeIdentifier`)
     */
    private void typeToBuffer(AST.Type t, AST.Dsymbol s, const bool canFixup = false)
    {
        debug (Debug_DtoH)
        {
            printf("[typeToBuffer(AST.Type, AST.Dsymbol) enter] %s sym %s\n", t.toChars(), s.toChars());
            scope(exit) printf("[typeToBuffer(AST.Type, AST.Dsymbol) exit] %s sym %s\n", t.toChars(), s.toChars());
        }

        // The context pointer (represented as `ThisDeclaration`) is named
        // `this` but accessible via `outer`
        if (auto td = s.isThisDeclaration())
        {
            import dmd.id;
            this.ident = Id.outer;
        }
        else
            this.ident = s.ident;

        auto type = origType !is null ? origType : t;
        AST.Dsymbol customLength;

        // Check for quirks that are usually resolved during semantic
        if (tdparent)
        {
            // Declarations within template declarations might use TypeAArray
            // instead of TypeSArray when the length is not an IntegerExp,
            // e.g. int[SOME_CONSTANT]
            if (auto taa = type.isTypeAArray())
            {
                // Try to resolve the symbol from the key if it's not an actual type
                Identifier id;
                if (auto ti = taa.index.isTypeIdentifier())
                    id = ti.ident;

                if (id)
                {
                    auto sym = findSymbol(id, adparent ? adparent : tdparent);
                    if (!sym)
                    {
                        // Couldn't resolve, assume actual AA
                    }
                    else if (AST.isType(sym))
                    {
                        // a real associative array, forward to visit
                    }
                    else if (auto vd = sym.isVarDeclaration())
                    {
                        // Actually a static array with length symbol
                        customLength = sym;
                        type = taa.next; // visit the element type, length is written below
                    }
                    else
                    {
                        printf("Resolved unexpected symbol while determining static array length: %s\n", sym.toChars());
                        fflush(stdout);
                        fatal();
                    }
                }
            }
        }
        type.accept(this);
        if (this.ident)
        {
            buf.writeByte(' ');
            // Custom identifier doesn't need further checks
            if (this.ident !is s.ident)
                buf.writestring(this.ident.toString());
            else
                writeIdentifier(s, canFixup);

        }
        this.ident = null;

        // Size is either taken from the type or resolved above
        auto tsa = t.isTypeSArray();
        if (tsa || customLength)
        {
            buf.writeByte('[');
            if (tsa)
                tsa.dim.accept(this);
            else
                writeFullName(customLength);
            buf.writeByte(']');
        }
        else if (t.isTypeNoreturn())
            buf.writestring("[0]");
    }

    override void visit(AST.Type t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);
        printf("Invalid type: %s\n", t.toPrettyChars());
        assert(0);
    }

    override void visit(AST.TypeNoreturn t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        buf.writestring("/* noreturn */ char");
    }

    override void visit(AST.TypeIdentifier t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        // Try to resolve the referenced symbol
        if (auto sym = findSymbol(t.ident))
            ensureDeclared(outermostSymbol(sym));

        if (t.idents.length)
            buf.writestring("typename ");

        writeIdentifier(t.ident, t.loc, "type", tdparent !is null);

        foreach (arg; t.idents)
        {
            buf.writestring("::");

            import dmd.root.rootobject;
            // Is this even possible?
            if (arg.dyncast != DYNCAST.identifier)
            {
                printf("arg.dyncast() = %d\n", arg.dyncast());
                assert(false);
            }
            buf.writestring((cast(Identifier) arg).toChars());
        }
    }

    override void visit(AST.TypeNull t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        if (global.params.cplusplus >= CppStdRevision.cpp11)
            buf.writestring("nullptr_t");
        else
            buf.writestring("void*");

    }

    override void visit(AST.TypeTypeof t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        assert(t.exp);

        if (t.exp.type)
        {
            t.exp.type.accept(this);
        }
        else if (t.exp.isThisExp())
        {
            // Short circuit typeof(this) => <Aggregate name>
            assert(adparent);
            buf.writestring(adparent.ident.toChars());
        }
        else
        {
            // Relying on C++'s typeof might produce wrong results
            // but it's the best we've got here.
            buf.writestring("typeof(");
            t.exp.accept(this);
            buf.writeByte(')');
        }
    }

    override void visit(AST.TypeBasic t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        if (t.isConst() || t.isImmutable())
            buf.writestring("const ");
        string typeName;
        switch (t.ty)
        {
            case AST.Tvoid:     typeName = "void";      break;
            case AST.Tbool:     typeName = "bool";      break;
            case AST.Tchar:     typeName = "char";      break;
            case AST.Twchar:    typeName = "char16_t";  break;
            case AST.Tdchar:    typeName = "char32_t";  break;
            case AST.Tint8:     typeName = "int8_t";    break;
            case AST.Tuns8:     typeName = "uint8_t";   break;
            case AST.Tint16:    typeName = "int16_t";   break;
            case AST.Tuns16:    typeName = "uint16_t";  break;
            case AST.Tint32:    typeName = "int32_t";   break;
            case AST.Tuns32:    typeName = "uint32_t";  break;
            case AST.Tint64:    typeName = "int64_t";   break;
            case AST.Tuns64:    typeName = "uint64_t";  break;
            case AST.Tfloat32:  typeName = "float";     break;
            case AST.Tfloat64:  typeName = "double";    break;
            case AST.Tfloat80:
                typeName = "_d_real";
                hasReal = true;
                break;
            case AST.Tcomplex32:  typeName = "_Complex float";  break;
            case AST.Tcomplex64:  typeName = "_Complex double"; break;
            case AST.Tcomplex80:
                typeName = "_Complex _d_real";
                hasReal = true;
                break;
            // ???: This is not strictly correct, but it should be ignored
            // in all places where it matters most (variables, functions, ...).
            case AST.Timaginary32: typeName = "float";  break;
            case AST.Timaginary64: typeName = "double"; break;
            case AST.Timaginary80:
                typeName = "_d_real";
                hasReal = true;
                break;
            default:
                //t.print();
                assert(0);
        }
        buf.writestring(typeName);
    }

    override void visit(AST.TypePointer t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        auto ts = t.next.isTypeStruct();
        if (ts && !strcmp(ts.sym.ident.toChars(), "__va_list_tag"))
        {
            buf.writestring("va_list");
            return;
        }

        // Pointer targets can be forward referenced
        const fwdSave = forwarding;
        forwarding = true;
        scope (exit) forwarding = fwdSave;

        t.next.accept(this);
        if (t.next.ty != AST.Tfunction)
            buf.writeByte('*');
        if (t.isConst() || t.isImmutable())
            buf.writestring(" const");
    }

    override void visit(AST.TypeSArray t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);
        t.next.accept(this);
    }

    override void visit(AST.TypeAArray t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);
        AST.Type.tvoidptr.accept(this);
    }

    override void visit(AST.TypeFunction tf)
    {
        debug (Debug_DtoH) mixin(traceVisit!tf);

        tf.next.accept(this);
        buf.writeByte('(');
        buf.writeByte('*');
        if (ident)
            buf.writestring(ident.toChars());
        ident = null;
        buf.writeByte(')');
        buf.writeByte('(');
        foreach (i, fparam; tf.parameterList)
        {
            if (i)
                buf.writestring(", ");
            fparam.accept(this);
        }
        if (tf.parameterList.varargs)
        {
            if (tf.parameterList.parameters.dim && tf.parameterList.varargs == 1)
                buf.writestring(", ");
            buf.writestring("...");
        }
        buf.writeByte(')');
    }

    ///  Writes the type that represents `ed` into `buf`.
    /// (Might not be `ed` for special enums or enums that were emitted as namespaces)
    private void enumToBuffer(AST.EnumDeclaration ed)
    {
        debug (Debug_DtoH) mixin(traceVisit!ed);

        if (ed.isSpecial())
        {
            if (ed.ident == DMDType.c_long)
                buf.writestring("long");
            else if (ed.ident == DMDType.c_ulong)
                buf.writestring("unsigned long");
            else if (ed.ident == DMDType.c_longlong)
                buf.writestring("long long");
            else if (ed.ident == DMDType.c_ulonglong)
                buf.writestring("unsigned long long");
            else if (ed.ident == DMDType.c_long_double)
                buf.writestring("long double");
            else if (ed.ident == DMDType.c_char)
                buf.writestring("char");
            else if (ed.ident == DMDType.c_wchar_t)
                buf.writestring("wchar_t");
            else if (ed.ident == DMDType.c_complex_float)
                buf.writestring("_Complex float");
            else if (ed.ident == DMDType.c_complex_double)
                buf.writestring("_Complex double");
            else if (ed.ident == DMDType.c_complex_real)
                buf.writestring("_Complex long double");
            else
            {
                //ed.print();
                assert(0);
            }
            return;
        }

        const kind = getEnumKind(ed.memtype);

        // Check if the enum was emitted as a real enum
        if (kind == EnumKind.Int || kind == EnumKind.Numeric)
        {
            writeFullName(ed);
        }
        else
        {
            // Use the base type if the enum was emitted as a namespace
            buf.printf("/* %s */ ", ed.ident.toChars());
            ed.memtype.accept(this);
        }
    }

    override void visit(AST.TypeEnum t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        if (t.isConst() || t.isImmutable())
            buf.writestring("const ");
        enumToBuffer(t.sym);
    }

    override void visit(AST.TypeStruct t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        if (t.isConst() || t.isImmutable())
            buf.writestring("const ");
        writeFullName(t.sym);
    }

    override void visit(AST.TypeDArray t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        if (t.isConst() || t.isImmutable())
            buf.writestring("const ");
        buf.writestring("_d_dynamicArray< ");
        t.next.accept(this);
        buf.writestring(" >");
    }

    override void visit(AST.TypeInstance t)
    {
        visitTi(t.tempinst);
    }

    private void visitTi(AST.TemplateInstance ti)
    {
        debug (Debug_DtoH) mixin(traceVisit!ti);

        // Ensure that the TD appears before the instance
        if (auto td = findTemplateDeclaration(ti))
            ensureDeclared(td);

        foreach (o; *ti.tiargs)
        {
            if (!AST.isType(o))
                return;
        }
        buf.writestring(ti.name.toChars());
        buf.writeByte('<');
        foreach (i, o; *ti.tiargs)
        {
            if (i)
                buf.writestring(", ");
            if (auto tt = AST.isType(o))
            {
                tt.accept(this);
            }
            else
            {
                //ti.print();
                //o.print();
                assert(0);
            }
        }
        buf.writestring(" >");
    }

    override void visit(AST.TemplateDeclaration td)
    {
        debug (Debug_DtoH) mixin(traceVisit!td);

        if (!shouldEmitAndMarkVisited(td))
            return;

        if (!td.parameters || !td.onemember || (!td.onemember.isStructDeclaration && !td.onemember.isClassDeclaration && !td.onemember.isFuncDeclaration))
        {
            visit(cast(AST.Dsymbol)td);
            return;
        }

        // Explicitly disallow templates with non-type parameters or specialization.
        foreach (p; *td.parameters)
        {
            if (!p.isTemplateTypeParameter() || p.specialization())
            {
                visit(cast(AST.Dsymbol)td);
                return;
            }
        }

        auto save = tdparent;
        tdparent = td;
        const bookmark = buf.length;
        printTemplateParams(td);

        const oldIgnored = this.ignoredCounter;
        td.onemember.accept(this);

        // Remove "template<...>" if the symbol could not be emitted
        if (oldIgnored != this.ignoredCounter)
            buf.setsize(bookmark);

        tdparent = save;
    }

    /// Writes the template<...> header for the supplied template declaration
    private void printTemplateParams(const AST.TemplateDeclaration td)
    {
        buf.writestring("template <");
        bool first = true;
        foreach (p; *td.parameters)
        {
            if (first)
                first = false;
            else
                buf.writestring(", ");
            buf.writestring("typename ");
            writeIdentifier(p.ident, p.loc, "template parameter", true);
        }
        buf.writestringln(">");
    }

    /// Emit declarations of the TemplateMixin in the current scope
    override void visit(AST.TemplateMixin tm)
    {
        debug (Debug_DtoH) mixin(traceVisit!tm);

        auto members = tm.members;

        // members are missing for instances inside of TemplateDeclarations, e.g.
        // template Foo(T) { mixin Bar!T; }
        if (!members)
        {
            if (auto td = findTemplateDeclaration(tm))
                members = td.members; // Emit members of the template
            else
                return; // Cannot emit mixin
        }

        foreach (s; *members)
        {
            // kind is undefined without semantic
            const kind = s.visible().kind;
            if (kind == AST.Visibility.Kind.public_ || kind == AST.Visibility.Kind.undefined)
                s.accept(this);
        }
    }

    /**
     * Finds a symbol with the identifier `name` by iterating the linked list of parent
     * symbols, starting from `context`.
     *
     * Returns: the symbol or `null` if missing
     */
    private AST.Dsymbol findSymbol(Identifier name, AST.Dsymbol context)
    {
        // Follow the declaration context
        for (auto par = context; par; par = par.toParentDecl())
        {
            // Check that `name` doesn't refer to a template parameter
            if (auto td = par.isTemplateDeclaration())
            {
                foreach (const p; *td.parameters)
                {
                    if (p.ident == name)
                        return null;
                }
            }

            if (auto mem = findMember(par, name))
            {
                return mem;
            }
        }
        return null;
    }

    /// ditto
    private AST.Dsymbol findSymbol(Identifier name)
    {
        AST.Dsymbol sym;
        if (adparent)
            sym = findSymbol(name, adparent);

        if (!sym && tdparent)
            sym = findSymbol(name, tdparent);

        return sym;
    }

    /// Finds the template declaration for instance `ti`
    private AST.TemplateDeclaration findTemplateDeclaration(AST.TemplateInstance ti)
    {
        if (ti.tempdecl)
            return ti.tempdecl.isTemplateDeclaration();

        assert(tdparent); // Only missing inside of templates

        // Search for the TemplateDeclaration, starting from the enclosing scope
        // if known or the enclosing template.
        auto sym = findSymbol(ti.name, ti.parent ? ti.parent : tdparent);
        return sym ? sym.isTemplateDeclaration() : null;
    }

    override void visit(AST.TypeClass t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        // Classes are emitted as pointer and hence can be forwarded
        const fwdSave = forwarding;
        forwarding = true;
        scope (exit) forwarding = fwdSave;

        if (t.isConst() || t.isImmutable())
            buf.writestring("const ");
        writeFullName(t.sym);
        buf.writeByte('*');
        if (t.isConst() || t.isImmutable())
            buf.writestring(" const");
    }

    /**
     * Writes the function signature to `buf`.
     *
     * Params:
     *   fd     = the function to print
     *   tf     = fd's type
     */
    private void funcToBuffer(AST.TypeFunction tf, AST.FuncDeclaration fd)
    {
        debug (Debug_DtoH)
        {
            printf("[funcToBuffer(AST.TypeFunction) enter] %s\n", fd.toChars());
            scope(exit) printf("[funcToBuffer(AST.TypeFunction) exit] %s\n", fd.toChars());
        }

        auto originalType = cast(AST.TypeFunction)fd.originalType;

        if (fd.isCtorDeclaration() || fd.isDtorDeclaration())
        {
            if (fd.isDtorDeclaration())
            {
                buf.writeByte('~');
            }
            buf.writestring(adparent.toChars());
            if (!tf)
            {
                assert(fd.isDtorDeclaration());
                buf.writestring("()");
                return;
            }
        }
        else
        {
            import dmd.root.string : toDString;
            assert(tf.next, fd.loc.toChars().toDString());

            tf.next == AST.Type.tsize_t ? originalType.next.accept(this) : tf.next.accept(this);
            if (tf.isref)
                buf.writeByte('&');
            buf.writeByte(' ');
            writeIdentifier(fd);
        }

        buf.writeByte('(');
        foreach (i, fparam; tf.parameterList)
        {
            if (i)
                buf.writestring(", ");
            if (fparam.type == AST.Type.tsize_t && originalType)
            {
                fparam = originalType.parameterList[i];
            }
            fparam.accept(this);
        }
        if (tf.parameterList.varargs)
        {
            if (tf.parameterList.parameters.dim && tf.parameterList.varargs == 1)
                buf.writestring(", ");
            buf.writestring("...");
        }
        buf.writeByte(')');
    }

    override void visit(AST.Parameter p)
    {
        debug (Debug_DtoH) mixin(traceVisit!p);

        ident = p.ident;

        {
            // Reference parameters can be forwarded
            const fwdStash = this.forwarding;
            this.forwarding = !!(p.storageClass & AST.STC.ref_);
            p.type.accept(this);
            this.forwarding = fwdStash;
        }

        if (p.storageClass & AST.STC.ref_)
            buf.writeByte('&');
        buf.writeByte(' ');
        if (ident)
            // FIXME: Parameter is missing a Loc
            writeIdentifier(ident, Loc.initial, "parameter", true);
        ident = null;

        if (p.defaultArg)
        {
            //printf("%s %d\n", p.defaultArg.toChars, p.defaultArg.op);
            buf.writestring(" = ");
            printExpressionFor(p.type, p.defaultArg);
        }
    }

    /**
     * Prints `exp` as an expression of type `target` while inserting
     * appropriate code when implicit conversion does not translate
     * directly to C++, e.g. from an enum to its base type.
     *
     * Params:
     *   target = the type `exp` is converted to
     *   exp    = the expression to print
     *   isCtor = if `exp` is a ctor argument
     */
    private void printExpressionFor(AST.Type target, AST.Expression exp, const bool isCtor = false)
    {
        /// Determines if a static_cast is required
        static bool needsCast(AST.Type target, AST.Expression exp)
        {
            // import std.stdio;
            // writefln("%s:%s: target = %s, type = %s (%s)", exp.loc.linnum, exp.loc.charnum, target, exp.type, exp.op);

            auto source = exp.type;

            // DotVarExp resolve conversions, e.g from an enum to its base type
            if (auto dve = exp.isDotVarExp())
                source = dve.var.type;

            if (!source)
                // Defensively assume that the cast is required
                return true;

            // Conversions from enum class to base type require static_cast
            if (global.params.cplusplus >= CppStdRevision.cpp11 &&
                source.isTypeEnum && !target.isTypeEnum)
                return true;

            return false;
        }

        // Slices are emitted as a special struct, hence we need to fix up
        // any expression initialising a slice variable/member
        if (auto ta = target.isTypeDArray())
        {
            if (exp.isNullExp())
            {
                if (isCtor)
                {
                    // Don't emit, use default ctor
                }
                else if (global.params.cplusplus >= CppStdRevision.cpp11)
                {
                    // Prefer initializer list
                    buf.writestring("{}");
                }
                else
                {
                    // Write __d_dynamic_array<TYPE>()
                    visit(ta);
                    buf.writestring("()");
                }
                return;
            }

            if (auto se = exp.isStringExp())
            {
                // Rewrite as <length> + <literal> pair optionally
                // wrapped in a initializer list/ctor call

                const initList = global.params.cplusplus >= CppStdRevision.cpp11;
                if (!isCtor)
                {
                    if (initList)
                        buf.writestring("{ ");
                    else
                    {
                        visit(ta);
                        buf.writestring("( ");
                    }
                }

                buf.printf("%zu, ", se.len);
                visit(se);

                if (!isCtor)
                    buf.writestring(initList ? " }" : " )");

                return;
            }
        }
        else if (auto ce = exp.isCastExp())
        {
            buf.writeByte('(');
            if (ce.to)
                ce.to.accept(this);
            else if (ce.e1.type)
                // Try the expression type with modifiers in case of cast(const) in templates
                ce.e1.type.castMod(ce.mod).accept(this);
            else
                // Fallback, not necessarily correct but the best we've got here
                target.accept(this);
            buf.writestring(") ");
            ce.e1.accept(this);
        }
        else if (needsCast(target, exp))
        {
            buf.writestring("static_cast<");
            target.accept(this);
            buf.writestring(">(");
            exp.accept(this);
            buf.writeByte(')');
        }
        else
        {
            exp.accept(this);
        }
    }

    override void visit(AST.Expression e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        // Valid in most cases, others should be overriden below
        // to use the appropriate operators  (:: and ->)
        buf.writestring(e.toString());
    }

    override void visit(AST.UnaExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        buf.writestring(expToString(e.op));
        e.e1.accept(this);
    }

    override void visit(AST.BinExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        e.e1.accept(this);
        buf.writeByte(' ');
        buf.writestring(expToString(e.op));
        buf.writeByte(' ');
        e.e2.accept(this);
    }

    /// Translates operator `op` into the C++ representation
    private extern(D) static string expToString(const EXP op)
    {
        switch (op) with (EXP)
        {
            case identity:      return "==";
            case notIdentity:   return "!=";
            default:
                return EXPtoString(op);
        }
    }

    override void visit(AST.VarExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        // Local members don't need another prefix and might've been renamed
        if (e.var.isThis())
        {
            includeSymbol(e.var);
            writeIdentifier(e.var, true);
        }
        else
            writeFullName(e.var);
    }

    /// Partially prints the FQN including parent aggregates
    private void printPrefix(AST.Dsymbol var)
    {
        if (!var || var is adparent || var.isModule())
            return;

        writeFullName(var);
        buf.writestring("::");
    }

    override void visit(AST.CallExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        // Dereferencing function pointers requires additional braces: (*f)(args)
        const isFp = e.e1.isPtrExp();
        if (isFp)
            buf.writeByte('(');
        else if (e.f)
            includeSymbol(outermostSymbol(e.f));

        e.e1.accept(this);

        if (isFp) buf.writeByte(')');

        assert(e.arguments);
        buf.writeByte('(');
        foreach (i, arg; *e.arguments)
        {
            if (i)
                buf.writestring(", ");
            arg.accept(this);
        }
        buf.writeByte(')');
    }

    override void visit(AST.DotVarExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        if (auto sym = symbolFromType(e.e1.type))
            includeSymbol(outermostSymbol(sym));

        // Accessing members through a pointer?
        if (auto pe = e.e1.isPtrExp)
        {
            pe.e1.accept(this);
            buf.writestring("->");
        }
        else
        {
            e.e1.accept(this);
            buf.writeByte('.');
        }

        // Should only be used to access non-static members
        assert(e.var.isThis());

        writeIdentifier(e.var, true);
    }

    override void visit(AST.DotIdExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        e.e1.accept(this);
        buf.writestring("::");
        buf.writestring(e.ident.toChars());
    }

    override void visit(AST.ScopeExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        // Usually a template instance in a TemplateDeclaration
        if (auto ti = e.sds.isTemplateInstance())
            visitTi(ti);
        else
            writeFullName(e.sds);
    }

    override void visit(AST.NullExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        if (global.params.cplusplus >= CppStdRevision.cpp11)
            buf.writestring("nullptr");
        else
            buf.writestring("NULL");
    }

    override void visit(AST.ArrayLiteralExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);
        buf.writestring("arrayliteral");
    }

    override void visit(AST.StringExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        if (e.sz == 2)
            buf.writeByte('u');
        else if (e.sz == 4)
            buf.writeByte('U');
        buf.writeByte('"');

        foreach (i; 0 .. e.len)
        {
            writeCharLiteral(*buf, e.getCodeUnit(i));
        }
        buf.writeByte('"');
    }

    override void visit(AST.RealExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);

        import dmd.root.ctfloat : CTFloat;

        // Special case NaN and Infinity because floatToBuffer
        // uses D literals (`nan` and `infinity`)
        if (CTFloat.isNaN(e.value))
        {
            buf.writestring("NAN");
        }
        else if (CTFloat.isInfinity(e.value))
        {
            if (e.value < CTFloat.zero)
                buf.writeByte('-');
            buf.writestring("INFINITY");
        }
        else
        {
            import dmd.hdrgen;
            // Hex floating point literals were introduced in C++ 17
            const allowHex = global.params.cplusplus >= CppStdRevision.cpp17;
            floatToBuffer(e.type, e.value, buf, allowHex);
        }
    }

    override void visit(AST.IntegerExp e)
    {
        debug (Debug_DtoH) mixin(traceVisit!e);
        visitInteger(e.toInteger, e.type);
    }

    /// Writes `v` as type `t` into `buf`
    private void visitInteger(dinteger_t v, AST.Type t)
    {
        debug (Debug_DtoH) mixin(traceVisit!t);

        switch (t.ty)
        {
            case AST.Tenum:
                auto te = cast(AST.TypeEnum)t;
                buf.writestring("(");
                enumToBuffer(te.sym);
                buf.writestring(")");
                visitInteger(v, te.sym.memtype);
                break;
            case AST.Tbool:
                buf.writestring(v ? "true" : "false");
                break;
            case AST.Tint8:
                buf.printf("%d", cast(byte)v);
                break;
            case AST.Tuns8:
                buf.printf("%uu", cast(ubyte)v);
                break;
            case AST.Tint16:
                buf.printf("%d", cast(short)v);
                break;
            case AST.Tuns16:
            case AST.Twchar:
                buf.printf("%uu", cast(ushort)v);
                break;
            case AST.Tint32:
            case AST.Tdchar:
                buf.printf("%d", cast(int)v);
                break;
            case AST.Tuns32:
                buf.printf("%uu", cast(uint)v);
                break;
            case AST.Tint64:
                buf.printf("%lldLL", v);
                break;
            case AST.Tuns64:
                buf.printf("%lluLLU", v);
                break;
            case AST.Tchar:
                if (v > 0x20 && v < 0x80)
                    buf.printf("'%c'", cast(int)v);
                else
                    buf.printf("%uu", cast(ubyte)v);
                break;
            default:
                //t.print();
                assert(0);
        }
    }

    override void visit(AST.StructLiteralExp sle)
    {
        debug (Debug_DtoH) mixin(traceVisit!sle);

        const isUnion = sle.sd.isUnionDeclaration();
        sle.sd.type.accept(this);
        buf.writeByte('(');
        foreach(i, e; *sle.elements)
        {
            if (i)
                buf.writestring(", ");

            auto vd = sle.sd.fields[i];

            // Expression may be null for unspecified elements
            if (!e)
                e = findDefaultInitializer(vd);

            printExpressionFor(vd.type, e);

            // Only emit the initializer of the first union member
            if (isUnion)
                break;
        }
        buf.writeByte(')');
    }

    /// Finds the default initializer for the given VarDeclaration
    private static AST.Expression findDefaultInitializer(AST.VarDeclaration vd)
    {
        if (vd._init && !vd._init.isVoidInitializer())
            return AST.initializerToExpression(vd._init);
        else if (auto ts = vd.type.isTypeStruct())
        {
            if (!ts.sym.noDefaultCtor && !ts.sym.isUnionDeclaration())
            {
                // Generate a call to the default constructor that we've generated.
                auto sle = new AST.StructLiteralExp(Loc.initial, ts.sym, new AST.Expressions(0));
                sle.type = vd.type;
                return sle;
            }
            else
                return vd.type.defaultInitLiteral(Loc.initial);
        }
        else
            return vd.type.defaultInitLiteral(Loc.initial);
    }

    static if (__VERSION__ < 2092)
    {
        private void ignored(const char* format, ...) nothrow
        {
            this.ignoredCounter++;

            import core.stdc.stdarg;
            if (!printIgnored)
                return;

            va_list ap;
            va_start(ap, format);
            buf.writestring("// Ignored ");
            buf.vprintf(format, ap);
            buf.writenl();
            va_end(ap);
        }
    }
    else
    {
        /// Writes a formatted message into `buf` if `printIgnored` is true
        /// and increments `ignoredCounter`
        pragma(printf)
        private void ignored(const char* format, ...) nothrow
        {
            this.ignoredCounter++;

            import core.stdc.stdarg;
            if (!printIgnored)
                return;

            va_list ap;
            va_start(ap, format);
            buf.writestring("// Ignored ");
            buf.vprintf(format, ap);
            buf.writenl();
            va_end(ap);
        }
    }

    /**
     * Determines whether `s` should be emitted. This requires that `sym`
     * - is `extern(C[++]`)
     * - is not instantiated from a template (visits the `TemplateDeclaration` instead)
     *
     * Params:
     *   sym = the symbol
     *
     * Returns: whether `sym` should be emitted
     */
    private bool shouldEmit(AST.Dsymbol sym)
    {
        import dmd.aggregate : ClassKind;
        debug (Debug_DtoH)
        {
            printf("[shouldEmitAndMarkVisited enter] %s\n", sym.toPrettyChars());
            scope(exit) printf("[shouldEmitAndMarkVisited exit] %s\n", sym.toPrettyChars());
        }

        // Template *instances* should not be emitted
        if (sym.isInstantiated())
            return false;

        // Matching linkage (except extern(C) classes which don't make sense)
        if (linkage == LINK.cpp || (linkage == LINK.c && !sym.isClassDeclaration()))
            return true;

        // Check against the internal information which might be missing, e.g. inside of template declarations
        if (auto dec = sym.isDeclaration())
        {
            const l = dec.resolvedLinkage();
            return l == LINK.cpp || l == LINK.c;
        }

        if (auto ad = sym.isAggregateDeclaration())
            return ad.classKind == ClassKind.cpp;

        return false;
    }

    /**
     * Determines whether `s` should be emitted. This requires that `sym`
     * - was not visited before
     * - is `extern(C[++]`)
     * - is not instantiated from a template (visits the `TemplateDeclaration` instead)
     * The result is cached in the visited nodes array.
     *
     * Params:
     *   sym = the symbol
     *
     * Returns: whether `sym` should be emitted
     **/
    private bool shouldEmitAndMarkVisited(AST.Dsymbol sym)
    {
        debug (Debug_DtoH)
        {
            printf("[shouldEmitAndMarkVisited enter] %s\n", sym.toPrettyChars());
            scope(exit) printf("[shouldEmitAndMarkVisited exit] %s\n", sym.toPrettyChars());
        }

        auto statePtr = (cast(void*) sym) in visited;

         // `sym` was already emitted or skipped and isn't required
        if (statePtr && (*statePtr || !mustEmit))
            return false;

        // Template *instances* should not be emitted, forward to the declaration
        if (auto ti = sym.isInstantiated())
        {
            auto td = findTemplateDeclaration(ti);
            assert(td);
            visit(td);
            return false;
        }

        // Required or matching linkage (except extern(C) classes which don't make sense)
        bool res = mustEmit || linkage == LINK.cpp || (linkage == LINK.c && !sym.isClassDeclaration());
        if (!res)
        {
            // Check against the internal information which might be missing, e.g. inside of template declarations
            if (auto dec = sym.isDeclaration())
            {
                const l = dec.resolvedLinkage();
                res = (l == LINK.cpp || l == LINK.c);
            }
        }

        // Remember result for later calls
        if (statePtr)
            *statePtr = res;
        else
            visited[(cast(void*) sym)] = res;

        // Print a warning when the symbol is ignored for the first time
        // Might not be correct if it is required by symbol the is visited
        // AFTER the current node
        if (!statePtr && !res)
            ignored("%s %s because of linkage", sym.kind(), sym.toPrettyChars());

        return res;
    }

    /**
     * Ensures that `sym` is declared before the current position in `buf` by
     * either creating a forward reference in `fwdbuf` if possible or
     * calling `includeSymbol` to emit the entire declaration into `donebuf`.
     */
    private void ensureDeclared(AST.Dsymbol sym)
    {
        auto par = sym.toParent2();
        auto ed = sym.isEnumDeclaration();

        // Eagerly include the symbol if we cannot create a valid forward declaration
        // Forwarding of scoped enums requires C++11 or above
        if (!forwarding || (par && !par.isModule()) || (ed && global.params.cplusplus < CppStdRevision.cpp11))
        {
            // Emit the entire enclosing declaration if any
            includeSymbol(outermostSymbol(sym));
            return;
        }

        auto ti = sym.isInstantiated();
        auto td = ti ? findTemplateDeclaration(ti) : null;
        auto check = cast(void*) (td ? td : sym);

        // Omit redundant fwd-declaration if we already emitted the entire declaration
        if (visited.get(check, false))
            return;

        // Already created a fwd-declaration?
        if (check in forwarded)
            return;
        forwarded[check] = true;

        // Print template<...>
        if (ti)
        {
            auto bufSave = buf;
            buf = fwdbuf;
            printTemplateParams(td);
            buf = bufSave;
        }

        // Determine the kind of symbol that is forwared: struct, ...
        const(char)* kind;

        if (auto ad = sym.isAggregateDeclaration())
        {
            // Look for extern(C++, class) <some aggregate>
            if (ad.cppmangle == CPPMANGLE.def)
                kind = ad.kind();
            else if (ad.cppmangle == CPPMANGLE.asStruct)
                kind =  "struct";
            else
                kind = "class";
        }
        else if (ed)
        {
            // Only called from enumToBuffer, so should always be emitted as an actual enum
            kind = "enum class";
        }
        else
            kind = sym.kind(); // Should be unreachable but just to be sure

        fwdbuf.writestring(kind);
        fwdbuf.writeByte(' ');
        fwdbuf.writestring(sym.toChars());
        fwdbuf.writestringln(";");
    }

    /**
     * Writes the qualified name of `sym` into `buf` including parent
     * symbols and template parameters.
     *
     * Params:
     *   sym         = the symbol
     *   mustInclude = whether sym may not be forward declared
     */
    private void writeFullName(AST.Dsymbol sym, const bool mustInclude = false)
    in
    {
        assert(sym);
        assert(sym.ident, sym.toString());
        // Should never be called directly with a TI, only onemember
        assert(!sym.isTemplateInstance(), sym.toString());
    }
    do
    {
        debug (Debug_DtoH)
        {
            printf("[writeFullName enter] %s\n", sym.toPrettyChars());
            scope(exit) printf("[writeFullName exit] %s\n", sym.toPrettyChars());
        }

        // Explicit `pragma(mangle, "<some string>` overrides the declared name
        if (auto mn = getMangleOverride(sym))
            return buf.writestring(mn);

        /// Checks whether `sym` is nested in `par` and hence doesn't need the FQN
        static bool isNestedIn(AST.Dsymbol sym, AST.Dsymbol par)
        {
            while (par)
            {
                if (sym is par)
                    return true;
                par = par.toParent();
            }
            return false;
        }
        AST.TemplateInstance ti;
        bool nested;

        // Check if the `sym` is nested into another symbol and hence requires `Parent::sym`
        if (auto par = sym.toParent())
        {
            // toParent() yields the template instance if `sym` is the onemember of a TI
            ti = par.isTemplateInstance();

            // Skip the TI because Foo!int.Foo is folded into Foo<int>
            if (ti) par = ti.toParent();

            // Prefix the name with any enclosing declaration
            // Stop at either module or enclosing aggregate
            nested = !par.isModule();
            if (nested && !isNestedIn(par, adparent))
            {
                writeFullName(par, true);
                buf.writestring("::");
            }
        }

        if (!nested)
        {
            // Cannot forward the symbol when called recursively
            // for a nested symbol
            if (mustInclude)
                includeSymbol(sym);
            else
                ensureDeclared(sym);
        }

        if (ti)
            visitTi(ti);
        else
            buf.writestring(sym.ident.toString());
    }

    /// Returns: Explicit mangling for `sym` if present
    extern(D) static const(char)[] getMangleOverride(const AST.Dsymbol sym)
    {
        if (auto decl = sym.isDeclaration())
            return decl.mangleOverride;

        return null;
    }
}

/// Namespace for identifiers used to represent special enums in C++
struct DMDType
{
    __gshared Identifier c_long;
    __gshared Identifier c_ulong;
    __gshared Identifier c_longlong;
    __gshared Identifier c_ulonglong;
    __gshared Identifier c_long_double;
    __gshared Identifier c_char;
    __gshared Identifier c_wchar_t;
    __gshared Identifier c_complex_float;
    __gshared Identifier c_complex_double;
    __gshared Identifier c_complex_real;

    static void _init()
    {
        c_long          = Identifier.idPool("__c_long");
        c_ulong         = Identifier.idPool("__c_ulong");
        c_longlong      = Identifier.idPool("__c_longlong");
        c_ulonglong     = Identifier.idPool("__c_ulonglong");
        c_long_double   = Identifier.idPool("__c_long_double");
        c_wchar_t       = Identifier.idPool("__c_wchar_t");
        c_char          = Identifier.idPool("__c_char");
        c_complex_float  = Identifier.idPool("__c_complex_float");
        c_complex_double = Identifier.idPool("__c_complex_double");
        c_complex_real = Identifier.idPool("__c_complex_real");
    }
}

/// Initializes all data structures used by the header generator
void initialize()
{
    __gshared bool initialized;

    if (!initialized)
    {
        initialized = true;

        DMDType._init();
    }
}

/// Writes `#if <content>` into the supplied buffer
void hashIf(ref OutBuffer buf, string content)
{
    buf.writestring("#if ");
    buf.writestringln(content);
}

/// Writes `#elif <content>` into the supplied buffer
void hashElIf(ref OutBuffer buf, string content)
{
    buf.writestring("#elif ");
    buf.writestringln(content);
}

/// Writes `#endif` into the supplied buffer
void hashEndIf(ref OutBuffer buf)
{
    buf.writestringln("#endif");
}

/// Writes `#define <content>` into the supplied buffer
void hashDefine(ref OutBuffer buf, string content)
{
    buf.writestring("#define ");
    buf.writestringln(content);
}

/// Writes `#include <content>` into the supplied buffer
void hashInclude(ref OutBuffer buf, string content)
{
    buf.writestring("#include ");
    buf.writestringln(content);
}

/// Determines whether `ident` is a reserved keyword in C++
/// Returns: the kind of keyword or `null`
const(char*) keywordClass(const Identifier ident)
{
    if (!ident)
        return null;

    const name = ident.toString();
    switch (name)
    {
        // C++ operators
        case "and":
        case "and_eq":
        case "bitand":
        case "bitor":
        case "compl":
        case "not":
        case "not_eq":
        case "or":
        case "or_eq":
        case "xor":
        case "xor_eq":
            return "special operator in C++";

        // C++ keywords
        case "_Complex":
        case "const_cast":
        case "delete":
        case "dynamic_cast":
        case "explicit":
        case "friend":
        case "inline":
        case "mutable":
        case "namespace":
        case "operator":
        case "register":
        case "reinterpret_cast":
        case "signed":
        case "static_cast":
        case "typedef":
        case "typename":
        case "unsigned":
        case "using":
        case "virtual":
        case "volatile":
            return "keyword in C++";

        // Common macros imported by this header
        // stddef.h
        case "offsetof":
        case "NULL":
            return "default macro in C++";

        // C++11 keywords
        case "alignas":
        case "alignof":
        case "char16_t":
        case "char32_t":
        case "constexpr":
        case "decltype":
        case "noexcept":
        case "nullptr":
        case "static_assert":
        case "thread_local":
        case "wchar_t":
            if (global.params.cplusplus >= CppStdRevision.cpp11)
                return "keyword in C++11";
            return null;

        // C++20 keywords
        case "char8_t":
        case "consteval":
        case "constinit":
        // Concepts-related keywords
        case "concept":
        case "requires":
        // Coroutines-related keywords
        case "co_await":
        case "co_yield":
        case "co_return":
            if (global.params.cplusplus >= CppStdRevision.cpp20)
                return "keyword in C++20";
            return null;

        default:
            // Identifiers starting with __ are reserved
            if (name.length >= 2 && name[0..2] == "__")
                return "reserved identifier in C++";

            return null;
    }
}

/// Finds the outermost symbol if `sym` is nested.
/// Returns `sym` if it appears at module scope
ASTCodegen.Dsymbol outermostSymbol(ASTCodegen.Dsymbol sym)
{
    assert(sym);
    while (true)
    {
        auto par = sym.toParent();
        if (!par || par.isModule())
            return sym;
        sym = par;
    }
}

/// Fetches the symbol for user-defined types from the type `t`
/// if `t` is either `TypeClass`, `TypeStruct` or `TypeEnum`
ASTCodegen.Dsymbol symbolFromType(ASTCodegen.Type t)
{
    if (auto tc = t.isTypeClass())
        return tc.sym;
    if (auto ts = t.isTypeStruct())
        return ts.sym;
    if (auto te = t.isTypeEnum())
        return te.sym;
    return null;
}

/**
 * Searches `sym` for a member with the given name.
 *
 * This method usually delegates to `Dsymbol.search` but might also
 * manually check the members if the symbol did not receive semantic
 * analysis.
 *
 * Params:
 *   sym  = symbol to search
 *   name = identifier of the requested symbol
 *
 * Returns: the symbol or `null` if not found
 */
ASTCodegen.Dsymbol findMember(ASTCodegen.Dsymbol sym, Identifier name)
{
    if (auto mem = sym.search(Loc.initial, name, ASTCodegen.IgnoreErrors))
        return mem;

    // search doesn't work for declarations inside of uninstantiated
    // `TemplateDeclaration`s due to the missing symtab.
    if (sym.semanticRun >= ASTCodegen.PASS.semanticdone)
        return null;

    // Manually check the members if present
    auto sds = sym.isScopeDsymbol();
    if (!sds || !sds.members)
        return null;

    /// Recursively searches for `name` without entering nested aggregates, ...
    static ASTCodegen.Dsymbol search(ASTCodegen.Dsymbols* members, Identifier name)
    {
        foreach (mem; *members)
        {
            if (mem.ident == name)
                return mem;

            // Look inside of private:, ...
            if (auto ad = mem.isAttribDeclaration())
            {
                if (auto s = search(ad.decl, name))
                    return s;
            }
        }
        return null;
    }

    return search(sds.members, name);
}

debug (Debug_DtoH)
{
    /// Generates code to trace the entry and exit of the enclosing `visit` function
    string traceVisit(alias node)()
    {
        const type = typeof(node).stringof;
        const method = __traits(hasMember, node, "toPrettyChars") ? "toPrettyChars" : "toChars";
        const arg = __traits(identifier, node) ~ '.' ~ method;

        return `printf("[` ~ type ~  ` enter] %s\n", ` ~ arg ~ `());
                scope(exit) printf("[` ~ type ~ ` exit] %s\n", ` ~ arg ~ `());`;
    }
}