- allow skipping optional arguments of the parent function in a virtual override definition.

This is mainly to allow retroactive addition to existing virtual functions without breaking existing content.
The MeansOfDeath fix for Actor.Die would not be possible without such handling.

src/dobjtype.cpp

@@ -776,16 +776,18 @@ PClass *PClass::FindClassTentative(FName name)
 //
 //==========================================================================
 
-int PClass::FindVirtualIndex(FName name, PPrototype *proto)
+int PClass::FindVirtualIndex(FName name, PFunction::Variant *variant, PFunction *parentfunc)
 {
+	auto proto = variant->Proto;
 	for (unsigned i = 0; i < Virtuals.Size(); i++)
 	{
 		if (Virtuals[i]->Name == name)
 		{
 			auto vproto = Virtuals[i]->Proto;
 			if (vproto->ReturnTypes.Size() != proto->ReturnTypes.Size() ||
-				vproto->ArgumentTypes.Size() != proto->ArgumentTypes.Size())
+				vproto->ArgumentTypes.Size() < proto->ArgumentTypes.Size())
 			{
+
 				continue;	// number of parameters does not match, so it's incompatible
 			}
 			bool fail = false;
@@ -808,7 +810,26 @@ int PClass::FindVirtualIndex(FName name, PPrototype *proto)
 					break;
 				}
 			}
-			if (!fail) return i;
+			if (!fail)
+			{
+				if (vproto->ArgumentTypes.Size() > proto->ArgumentTypes.Size() && parentfunc)
+				{
+					// Check if the difference between both functions is only some optional arguments.
+					for (unsigned a = proto->ArgumentTypes.Size(); a < vproto->ArgumentTypes.Size(); a++)
+					{
+						if (!(parentfunc->Variants[0].ArgFlags[a] & VARF_Optional)) return -1;
+					}
+
+					// Todo: extend the prototype
+					for (unsigned a = proto->ArgumentTypes.Size(); a < vproto->ArgumentTypes.Size(); a++)
+					{
+						proto->ArgumentTypes.Push(vproto->ArgumentTypes[a]);
+						variant->ArgFlags.Push(parentfunc->Variants[0].ArgFlags[a]);
+						variant->ArgNames.Push(NAME_None);
+					}
+				}
+				return i;
+			}
 		}
 	}
 	return -1;

src/dobjtype.h

@@ -42,7 +42,7 @@ public:
 	void WriteAllFields(FSerializer &ar, const void *addr) const;
 	bool ReadAllFields(FSerializer &ar, void *addr) const;
 	void InitializeDefaults();
-	int FindVirtualIndex(FName name, PPrototype *proto);
+	int FindVirtualIndex(FName name, PFunction::Variant *variant, PFunction *parentfunc);
 	PSymbol *FindSymbol(FName symname, bool searchparents) const;
 	PField *AddField(FName name, PType *type, uint32_t flags);
 

src/scripting/zscript/zcc_compile.cpp

@@ -2694,7 +2694,9 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 
 			if (forclass)
 			{
-				int vindex = clstype->FindVirtualIndex(sym->SymbolName, sym->Variants[0].Proto);
+				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);
 				// specifying 'override' is necessary to prevent one of the biggest problem spots with virtual inheritance: Mismatching argument types.
 				if (varflags & VARF_Override)
 				{
@@ -2705,7 +2707,6 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 					else
 					{
 						auto oldfunc = clstype->Virtuals[vindex];
-						auto parentfunc = dyn_cast<PFunction>(clstype->ParentClass->VMType->Symbols.FindSymbol(sym->SymbolName, true));
 						if (parentfunc && parentfunc->mVersion > mVersion)
 						{
 							Error(f, "Attempt to override function %s which is incompatible with version %d.%d.%d", FName(f->Name).GetChars(), mVersion.major, mVersion.minor, mVersion.revision);
@@ -2765,7 +2766,7 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 		}
 		else if (forclass)
 		{
-			int vindex = clstype->FindVirtualIndex(sym->SymbolName, sym->Variants[0].Proto);
+			int vindex = clstype->FindVirtualIndex(sym->SymbolName, &sym->Variants[0], nullptr);
 			if (vindex != -1)
 			{
 				Error(f, "Function %s attempts to override parent function without 'override' qualifier", FName(f->Name).GetChars());