Added warning for uninitialized variables in ZScript

https://forum.zdoom.org/viewtopic.php?t=57868

src/scripting/backend/codegen.cpp

@@ -2692,6 +2692,7 @@ FxExpression *FxMultiAssign::Resolve(FCompileContext &ctx)
 	for (unsigned i = 0; i < Base.Size(); i++)
 	{
 		auto singlevar = new FxLocalVariableDeclaration(rets[i], NAME_None, nullptr, 0, ScriptPosition);
+		singlevar->IsInitialized = true;
 		LocalVarContainer->Add(singlevar);
 		Base[i] = Base[i]->Resolve(ctx);
 		ABORT(Base[i]);
@@ -6031,7 +6032,7 @@ FxExpression *FxIdentifier::Resolve(FCompileContext& ctx)
 		}
 		else
 		{
-			auto x = new FxStackVariable(local->ValueType, local->StackOffset, ScriptPosition);
+			auto x = new FxStackVariable(local, ScriptPosition);
 			delete this;
 			return x->Resolve(ctx);
 		}
@@ -6520,6 +6521,7 @@ FxLocalVariable::FxLocalVariable(FxLocalVariableDeclaration *var, const FScriptP
 FxExpression *FxLocalVariable::Resolve(FCompileContext &ctx)
 {
 	CHECKRESOLVED();
+	IsLocalVariable = ctx.FunctionArgs.Find(Variable) == ctx.FunctionArgs.Size();
 	return this;
 }
 
@@ -6553,7 +6555,16 @@ ExpEmit FxLocalVariable::Emit(VMFunctionBuilder *build)
 	{
 		ExpEmit ret(Variable->RegNum + RegOffset, Variable->ValueType->GetRegType(), false, true);
 		ret.RegCount = ValueType->GetRegCount();
-		if (AddressRequested) ret.Target = true;
+		if (AddressRequested)
+		{
+			Variable->IsInitialized = true;
+			ret.Target = true;
+		}
+		else if (IsLocalVariable)
+		{
+			Variable->WarnIfUninitialized(ScriptPosition);
+		}
+
 		return ret;
 	}
 }
@@ -6895,8 +6906,9 @@ ExpEmit FxCVar::Emit(VMFunctionBuilder *build)
 //
 //==========================================================================
 
-FxStackVariable::FxStackVariable(PType *type, int offset, const FScriptPosition &pos)
+FxStackVariable::FxStackVariable(FxLocalVariableDeclaration *var, const FScriptPosition &pos)
-	: FxMemberBase(EFX_StackVariable, Create<PField>(NAME_None, type, 0, offset), pos)
+	: FxMemberBase(EFX_StackVariable, Create<PField>(NAME_None, var->ValueType, 0, var->StackOffset), pos)
+	, Variable(var)
 {
 }
 
@@ -6947,6 +6959,8 @@ ExpEmit FxStackVariable::Emit(VMFunctionBuilder *build)
 
 	if (AddressRequested)
 	{
+		Variable->IsInitialized = true;
+
 		if (offsetreg >= 0)
 		{
 			ExpEmit obj(build, REGT_POINTER);
@@ -6958,6 +6972,10 @@ ExpEmit FxStackVariable::Emit(VMFunctionBuilder *build)
 			return build->FramePointer;
 		}
 	}
+	else
+	{
+		Variable->WarnIfUninitialized(ScriptPosition);
+	}
 	ExpEmit loc(build, membervar->Type->GetRegType(), membervar->Type->GetRegCount());
 
 	if (membervar->BitValue == -1)
@@ -11403,6 +11421,16 @@ void FxLocalVariableDeclaration::Release(VMFunctionBuilder *build)
 	// For that all local stack variables need to live for the entire execution of a function.
 }
 
+void FxLocalVariableDeclaration::WarnIfUninitialized(const FScriptPosition &varPos) const
+{
+	if (!IsInitialized && nullptr == Init)
+	{
+		varPos.Message(MSG_WARNING,
+			"Usage of uninitialized variable '%s' defined at line %i",
+			Name.GetChars(), ScriptPosition.ScriptLine);
+	}
+}
+
 
 FxStaticArray::FxStaticArray(PType *type, FName name, FArgumentList &args, const FScriptPosition &pos)
 	: FxLocalVariableDeclaration(NewArray(type, args.Size()), name, nullptr, VARF_Static|VARF_ReadOnly, pos)

src/scripting/backend/codegen.h

@@ -1425,6 +1425,7 @@ class FxLocalVariable : public FxExpression
 public:
 	FxLocalVariableDeclaration *Variable;
 	bool AddressRequested;
+	bool IsLocalVariable; // false for function parameter and true otherwise
 	int RegOffset;
 
 	FxLocalVariable(FxLocalVariableDeclaration*, const FScriptPosition&);
@@ -1442,7 +1443,9 @@ public:
 class FxStackVariable : public FxMemberBase
 {
 public:
-	FxStackVariable(PType *type, int offset, const FScriptPosition&);
+	FxLocalVariableDeclaration *Variable;
+
+	FxStackVariable(FxLocalVariableDeclaration*, const FScriptPosition&);
 	~FxStackVariable();
 	FxExpression *Resolve(FCompileContext&);
 	bool RequestAddress(FCompileContext &ctx, bool *writable);
@@ -2121,6 +2124,7 @@ class FxLocalVariableDeclaration : public FxExpression
 {
 	friend class FxCompoundStatement;
 	friend class FxLocalVariable;
+	friend class FxStackVariable;
 	friend class FxStaticArrayVariable;
 
 	FName Name;
@@ -2130,6 +2134,7 @@ class FxLocalVariableDeclaration : public FxExpression
 public:
 	int StackOffset = -1;
 	int RegNum = -1;
+	bool IsInitialized = false;
 
 	FxLocalVariableDeclaration(PType *type, FName name, FxExpression *initval, int varflags, const FScriptPosition &p);
 	~FxLocalVariableDeclaration();
@@ -2137,7 +2142,7 @@ public:
 	ExpEmit Emit(VMFunctionBuilder *build);
 	void Release(VMFunctionBuilder *build);
 	void SetReg(ExpEmit reginfo);
-
+	void WarnIfUninitialized(const FScriptPosition &varPos) const;
 };
 
 //==========================================================================