- Implement return type covariance for ZScript virtual functions

src/common/objects/dobjtype.cpp

@@ -51,6 +51,7 @@
 // TYPES -------------------------------------------------------------------
 
 // EXTERNAL FUNCTION PROTOTYPES --------------------------------------------
+bool AreCompatiblePointerTypes(PType* dest, PType* source, bool forcompare = false);
 
 // PUBLIC FUNCTION PROTOTYPES ----------------------------------------------
 
@@ -665,7 +666,7 @@ PClass *PClass::FindClassTentative(FName name)
 //
 //==========================================================================
 
-int PClass::FindVirtualIndex(FName name, PFunction::Variant *variant, PFunction *parentfunc)
+int PClass::FindVirtualIndex(FName name, PFunction::Variant *variant, PFunction *parentfunc, bool exactReturnType)
 {
 	auto proto = variant->Proto;
 	for (unsigned i = 0; i < Virtuals.Size(); i++)
@@ -693,7 +694,10 @@ int PClass::FindVirtualIndex(FName name, PFunction::Variant *variant, PFunction
 
 			for (unsigned a = 0; a < proto->ReturnTypes.Size(); a++)
 			{
-				if (proto->ReturnTypes[a] != vproto->ReturnTypes[a])
+				PType* expected = vproto->ReturnTypes[a];
+				PType* actual = proto->ReturnTypes[a];
+
+				if (expected != actual && (exactReturnType || !AreCompatiblePointerTypes(expected, actual)))
 				{
 					fail = true;
 					break;

src/common/objects/dobjtype.h

@@ -43,7 +43,7 @@ public:
 	void InitializeSpecials(void* addr, void* defaults, TArray<FTypeAndOffset> PClass::* Inits);
 	void WriteAllFields(FSerializer &ar, const void *addr) const;
 	bool ReadAllFields(FSerializer &ar, void *addr) const;
-	int FindVirtualIndex(FName name, PFunction::Variant *variant, PFunction *parentfunc);
+	int FindVirtualIndex(FName name, PFunction::Variant *variant, PFunction *parentfunc, bool exactReturnType);
 	PSymbol *FindSymbol(FName symname, bool searchparents) const;
 	PField *AddField(FName name, PType *type, uint32_t flags);
 	void InitializeDefaults();

src/common/scripting/backend/codegen.cpp

@@ -81,7 +81,7 @@ static const FLOP FxFlops[] =
 	{ NAME_Round,	FLOP_ROUND,		[](double v) { return round(v);  } },
 };
 
-static bool AreCompatiblePointerTypes(PType* dest, PType* source, bool forcompare = false);
+bool AreCompatiblePointerTypes(PType* dest, PType* source, bool forcompare = false);
 
 //==========================================================================
 //
@@ -271,7 +271,7 @@ PFunction *FindBuiltinFunction(FName funcname)
 //
 //==========================================================================
 
-static bool AreCompatiblePointerTypes(PType *dest, PType *source, bool forcompare)
+bool AreCompatiblePointerTypes(PType *dest, PType *source, bool forcompare)
 {
 	if (dest->isPointer() && source->isPointer())
 	{

src/common/scripting/frontend/zcc_compile.cpp

@@ -2366,6 +2366,7 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 			sym->Variants[0].Implementation->VarFlags = sym->Variants[0].Flags;
 		}
 
+		bool exactReturnType = mVersion < MakeVersion(4, 4);
 		PClass *clstype = forclass? static_cast<PClassType *>(c->Type())->Descriptor : nullptr;
 		if (varflags & VARF_Virtual)
 		{
@@ -2379,7 +2380,7 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 			{
 				auto parentfunc = clstype->ParentClass? dyn_cast<PFunction>(clstype->ParentClass->VMType->Symbols.FindSymbol(sym->SymbolName, true)) : nullptr;
 
-				int vindex = clstype->FindVirtualIndex(sym->SymbolName, &sym->Variants[0], parentfunc);
+				int vindex = clstype->FindVirtualIndex(sym->SymbolName, &sym->Variants[0], parentfunc, exactReturnType);
 				// specifying 'override' is necessary to prevent one of the biggest problem spots with virtual inheritance: Mismatching argument types.
 				if (varflags & VARF_Override)
 				{
@@ -2459,7 +2460,7 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 		}
 		else if (forclass)
 		{
-			int vindex = clstype->FindVirtualIndex(sym->SymbolName, &sym->Variants[0], nullptr);
+			int vindex = clstype->FindVirtualIndex(sym->SymbolName, &sym->Variants[0], nullptr, exactReturnType);
 			if (vindex != -1)
 			{
 				Error(f, "Function %s attempts to override parent function without 'override' qualifier", FName(f->Name).GetChars());

wadsrc/static/zscript.txt

@@ -1,4 +1,4 @@
-version "4.3"
+version "4.4"
 #include "zscript/base.zs"
 #include "zscript/sounddata.zs"
 #include "zscript/mapdata.zs"

wadsrc_extra/static/filter/harmony/zscript.txt

@@ -1,2 +1,2 @@
-version "4.2"
+version "4.4"
 #include "zscript/harm_sbar.zs"