Re-allow indexes as state parameter in sequences

src/namedef.h

@@ -654,6 +654,7 @@ xx(DecoCallLineSpecial)
 xx(DecoNameToClass)
 xx(DecoFindMultiNameState)
 xx(DecoFindSingleNameState)
+xx(DecoHandleRuntimeState)
 xx(Damage)
 
 // basic type names

src/thingdef/thingdef_exp.h

@@ -1058,6 +1058,24 @@ public:
 	FxExpression *Resolve(FCompileContext&);
 };
 
+//==========================================================================
+//
+// Same as above except for expressions which means it will have to be
+// evaluated at runtime
+//
+//==========================================================================
+
+class FxRuntimeStateIndex : public FxExpression
+{
+	FxExpression *Index;
+
+public:
+	FxRuntimeStateIndex(FxExpression *index);
+	~FxRuntimeStateIndex();
+	FxExpression *Resolve(FCompileContext&);
+	ExpEmit Emit(VMFunctionBuilder *build);
+};
+
 //==========================================================================
 //
 //

src/thingdef/thingdef_expression.cpp

@@ -4429,6 +4429,89 @@ FxExpression *FxStateByIndex::Resolve(FCompileContext &ctx)
 	return x;
 }
 
+//==========================================================================
+//
+//
+//
+//==========================================================================
+
+FxRuntimeStateIndex::FxRuntimeStateIndex(FxExpression *index)
+: FxExpression(index->ScriptPosition), Index(index)
+{
+	ValueType = TypeState;
+}
+
+FxRuntimeStateIndex::~FxRuntimeStateIndex()
+{
+	SAFE_DELETE(Index);
+}
+
+FxExpression *FxRuntimeStateIndex::Resolve(FCompileContext &ctx)
+{
+	CHECKRESOLVED();
+	SAFE_RESOLVE(Index, ctx);
+
+	if (!Index->IsNumeric())
+	{
+		ScriptPosition.Message(MSG_ERROR, "Numeric type expected");
+		delete this;
+		return nullptr;
+	}
+	else if (Index->ValueType->GetRegType() != REGT_INT)
+	{ // Float.
+		Index = new FxIntCast(Index);
+		SAFE_RESOLVE(Index, ctx);
+	}
+
+	return this;
+}
+
+static int DecoHandleRuntimeState(VMFrameStack *stack, VMValue *param, int numparam, VMReturn *ret, int numret)
+{
+	PARAM_PROLOGUE;
+	PARAM_OBJECT(stateowner, AActor);
+	PARAM_POINTER(stateinfo, FStateParamInfo);
+	PARAM_INT(index);
+
+	if (index == 0 || !stateowner->GetClass()->OwnsState(stateinfo->mCallingState + index))
+	{
+		// Null is returned if the location was invalid which means that no jump will be performed
+		// if used as return value
+		// 0 always meant the same thing so we handle it here for compatibility
+		ret->SetPointer(nullptr, ATAG_STATE);
+	}
+	else
+	{
+		ret->SetPointer(stateinfo->mCallingState + index, ATAG_STATE);
+	}
+
+	return 1;
+}
+
+ExpEmit FxRuntimeStateIndex::Emit(VMFunctionBuilder *build)
+{
+	assert(build->Registers[REGT_POINTER].GetMostUsed() >= 3);
+
+	ExpEmit out(build, REGT_POINTER);
+
+	build->Emit(OP_PARAM, 0, REGT_POINTER, 1); // stateowner
+	build->Emit(OP_PARAM, 0, REGT_POINTER, 2); // stateinfo
+	ExpEmit id = Index->Emit(build);
+	build->Emit(OP_PARAM, 0, REGT_INT | (id.Konst ? REGT_KONST : 0), id.RegNum); // index
+
+	VMFunction *callfunc;
+	PSymbol *sym;
+	
+	sym = FindDecorateBuiltinFunction(NAME_DecoHandleRuntimeState, DecoHandleRuntimeState);
+	assert(sym->IsKindOf(RUNTIME_CLASS(PSymbolVMFunction)));
+	assert(((PSymbolVMFunction *)sym)->Function != nullptr);
+	callfunc = ((PSymbolVMFunction *)sym)->Function;
+
+	build->Emit(OP_CALL_K, build->GetConstantAddress(callfunc, ATAG_OBJECT), 3, 1);
+	build->Emit(OP_RESULT, 0, REGT_POINTER, out.RegNum);
+
+	return out;
+}
 
 //==========================================================================
 //

src/thingdef/thingdef_parse.cpp

@@ -138,7 +138,8 @@ FxExpression *ParseParameter(FScanner &sc, PClassActor *cls, PType *type, bool c
 	else if (type == TypeState)
 	{
 		// This forces quotation marks around the state name.
-		sc.MustGetToken(TK_StringConst);
+		if (sc.CheckToken(TK_StringConst))
+		{
 			if (sc.String[0] == 0 || sc.Compare("None"))
 			{
 				x = new FxConstant((FState*)NULL, sc);
@@ -156,6 +157,12 @@ FxExpression *ParseParameter(FScanner &sc, PClassActor *cls, PType *type, bool c
 				x = new FxMultiNameState(sc.String, sc);
 			}
 		}
+		else if (!constant)
+		{
+			x = new FxRuntimeStateIndex(ParseExpression(sc, cls));
+		}
+		else sc.MustGetToken(TK_StringConst); // This is for the error.
+	}
 	else if (type->GetClass() == RUNTIME_CLASS(PClassPointer))
 	{	// Actor name
 		sc.SetEscape(true);