Fix issue 20700 - Fwd refs leads to extern(C++, class|struct) being i…

…gnored

`Type`-derived AST nodes do not support the same kind of semantic analysis that
`Dsymbol`-derived one do. The issue was that in some codes, semantic analysis on
the type was performed before it was performed on the declaration,
and chasing those cases turned out to be endless, hence the minor refactoring.

src/dmd/aggregate.d

@@ -85,6 +85,10 @@ extern (C++) abstract class AggregateDeclaration : ScopeDsymbol
 
     /// specifies whether this is a D, C++, Objective-C or anonymous struct/class/interface
     ClassKind classKind;
+    /// Specify whether to mangle the aggregate as a `class` or a `struct`
+    /// This information is used by the MSVC mangler
+    /// Only valid for class and struct. TODO: Merge with ClassKind ?
+    CPPMANGLE cppmangle;
 
     /* !=null if is nested
      * pointing to the dsymbol that directly enclosing it.

src/dmd/aggregate.h

@@ -84,6 +84,7 @@ class AggregateDeclaration : public ScopeDsymbol
     Dsymbol *deferred;          // any deferred semantic2() or semantic3() symbol
 
     ClassKind::Type classKind;  // specifies the linkage type
+    CPPMANGLE cppmangle;
 
     /* !=NULL if is nested
      * pointing to the dsymbol that directly enclosing it.

src/dmd/attrib.d

@@ -442,6 +442,13 @@ extern (C++) final class CPPMangleDeclaration : AttribDeclaration
             sc.aligndecl, sc.inlining);
     }
 
+    override void setScope(Scope* sc)
+    {
+        if (decl)
+            Dsymbol.setScope(sc); // for forward reference
+        return AttribDeclaration.setScope(sc);
+    }
+
     override const(char)* toChars() const
     {
         return toString().ptr;

src/dmd/attrib.h

@@ -87,6 +87,7 @@ class CPPMangleDeclaration : public AttribDeclaration
 
     Dsymbol *syntaxCopy(Dsymbol *s);
     Scope *newScope(Scope *sc);
+    void setScope(Scope *sc);
     const char *toChars() const;
     void accept(Visitor *v) { v->visit(this); }
 };

src/dmd/cppmanglewin.d

@@ -16,8 +16,10 @@ import core.stdc.stdio;
 
 import dmd.arraytypes;
 import dmd.cppmangle : isPrimaryDtor, isCppOperator, CppOperator;
+import dmd.dclass;
 import dmd.declaration;
 import dmd.denum : isSpecialEnumIdent;
+import dmd.dstruct;
 import dmd.dsymbol;
 import dmd.dtemplate;
 import dmd.errors;
@@ -385,11 +387,12 @@ public:
             return;
         //printf("visit(TypeStruct); is_not_top_type = %d\n", (int)(flags & IS_NOT_TOP_TYPE));
         mangleModifier(type);
-        if (type.sym.isUnionDeclaration())
+        auto agg = cast(StructDeclaration) type.sym;
+        if (agg.isUnionDeclaration())
             buf.writeByte('T');
         else
-            buf.writeByte(type.cppmangle == CPPMANGLE.asClass ? 'V' : 'U');
-        mangleIdent(type.sym);
+            buf.writeByte(agg.cppmangle == CPPMANGLE.asClass ? 'V' : 'U');
+        mangleIdent(agg);
         flags &= ~IS_NOT_TOP_TYPE;
         flags &= ~IGNORE_CONST;
     }
@@ -456,8 +459,9 @@ public:
             buf.writeByte('E');
         flags |= IS_NOT_TOP_TYPE;
         mangleModifier(type);
-        buf.writeByte(type.cppmangle == CPPMANGLE.asStruct ? 'U' : 'V');
-        mangleIdent(type.sym);
+        auto cldecl = cast(ClassDeclaration) type.sym;
+        buf.writeByte(cldecl.cppmangle == CPPMANGLE.asStruct ? 'U' : 'V');
+        mangleIdent(cldecl);
         flags &= ~IS_NOT_TOP_TYPE;
         flags &= ~IGNORE_CONST;
     }

src/dmd/dsymbolsem.d

@@ -4639,6 +4639,7 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
             if (sc.linkage == LINK.cpp)
                 sd.classKind = ClassKind.cpp;
             sd.cppnamespace = sc.namespace;
+            sd.cppmangle = sc.cppmangle;
         }
         else if (sd.symtab && !scx)
             return;
@@ -4857,6 +4858,7 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
             if (sc.linkage == LINK.cpp)
                 cldec.classKind = ClassKind.cpp;
             cldec.cppnamespace = sc.namespace;
+            cldec.cppmangle = sc.cppmangle;
             if (sc.linkage == LINK.objc)
                 objc.setObjc(cldec);
         }

src/dmd/mtype.h

@@ -725,7 +725,6 @@ class TypeStruct : public Type
 public:
     StructDeclaration *sym;
     AliasThisRec att;
-    CPPMANGLE cppmangle;
 
     static TypeStruct *create(StructDeclaration *sym);
     const char *kind();

src/dmd/typesem.d

@@ -1812,14 +1812,7 @@ extern(C++) Type typeSemantic(Type t, Loc loc, Scope* sc)
     {
         //printf("TypeStruct::semantic('%s')\n", mtype.toChars());
         if (mtype.deco)
-        {
-            if (sc && sc.cppmangle != CPPMANGLE.def)
-            {
-                if (mtype.cppmangle == CPPMANGLE.def)
-                    mtype.cppmangle = sc.cppmangle;
-            }
             return mtype;
-        }
 
         /* Don't semantic for sym because it should be deferred until
          * sizeof needed or its members accessed.
@@ -1830,11 +1823,6 @@ extern(C++) Type typeSemantic(Type t, Loc loc, Scope* sc)
         if (mtype.sym.type.ty == Terror)
             return error();
 
-        if (sc && sc.cppmangle != CPPMANGLE.def)
-            mtype.cppmangle = sc.cppmangle;
-        else
-            mtype.cppmangle = CPPMANGLE.asStruct;
-
         return merge(mtype);
     }
 
@@ -1848,14 +1836,7 @@ extern(C++) Type typeSemantic(Type t, Loc loc, Scope* sc)
     {
         //printf("TypeClass::semantic(%s)\n", mtype.toChars());
         if (mtype.deco)
-        {
-            if (sc && sc.cppmangle != CPPMANGLE.def)
-            {
-                if (mtype.cppmangle == CPPMANGLE.def)
-                    mtype.cppmangle = sc.cppmangle;
-            }
             return mtype;
-        }
 
         /* Don't semantic for sym because it should be deferred until
          * sizeof needed or its members accessed.
@@ -1866,11 +1847,6 @@ extern(C++) Type typeSemantic(Type t, Loc loc, Scope* sc)
         if (mtype.sym.type.ty == Terror)
             return error();
 
-        if (sc && sc.cppmangle != CPPMANGLE.def)
-            mtype.cppmangle = sc.cppmangle;
-        else
-            mtype.cppmangle = CPPMANGLE.asClass;
-
         return merge(mtype);
     }
 

test/compilable/cppmangle.d

@@ -1251,3 +1251,15 @@ extern(C++, `bar`)
 {
     void func19542(T)();
 }
+
+// https://issues.dlang.org/show_bug.cgi?id=20700
+version (Windows) extern(C++)
+{
+    void test20700_1(Struct20700);
+    extern(C++, class) struct Struct20700 {}
+    void test20700_2(Struct20700);
+
+    // Note: Needs to be `BV` (`class`), not `BU` (`struct`)
+    static assert(test20700_1.mangleof == `?test20700_1@@YAXVStruct20700@@@Z`);
+    static assert(test20700_2.mangleof == `?test20700_2@@YAXVStruct20700@@@Z`);
+}