From 7d3663500f5f9f47aebacb3dc3be274a99263bc3 Mon Sep 17 00:00:00 2001
From: ZZYZX <zzyzx@virtual>
Date: Thu, 16 Feb 2017 02:39:49 +0200
Subject: [PATCH] Disallow creation of abstract classes outside of their own
 class (this is so that modders can create their own factory methods, not just
 for native)

---
 src/dobject.h                     |  2 +-
 src/scripting/backend/codegen.cpp | 17 +++++++++++++++--
 src/scripting/backend/codegen.h   |  1 +
 src/scripting/vm/vmexec.h         |  3 ++-
 4 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/dobject.h b/src/dobject.h
index ce4714010e..01ee76fb2a 100644
--- a/src/dobject.h
+++ b/src/dobject.h
@@ -205,7 +205,7 @@ enum EObjectFlags
 	OF_Transient		= 1 << 11,		// Object should not be archived (references to it will be nulled on disk)
 	OF_Spawned			= 1 << 12,      // Thinker was spawned at all (some thinkers get deleted before spawning)
 	OF_Released			= 1 << 13,		// Object was released from the GC system and should not be processed by GC function
-	OF_Abstract			= 1 << 14,		// Marks a class that cannot be created with CreateNew
+	OF_Abstract			= 1 << 14,		// Marks a class that cannot be created with new() function
 };
 
 template<class T> class TObjPtr;
diff --git a/src/scripting/backend/codegen.cpp b/src/scripting/backend/codegen.cpp
index db7d7425fe..551378d8bc 100644
--- a/src/scripting/backend/codegen.cpp
+++ b/src/scripting/backend/codegen.cpp
@@ -5023,6 +5023,7 @@ FxNew::FxNew(FxExpression *v)
 {
 	val = new FxClassTypeCast(NewClassPointer(RUNTIME_CLASS(DObject)), v, false);
 	ValueType = NewPointer(RUNTIME_CLASS(DObject));
+	CallingClass = nullptr;
 }
 
 //==========================================================================
@@ -5047,6 +5048,7 @@ FxExpression *FxNew::Resolve(FCompileContext &ctx)
 	CHECKRESOLVED();
 	SAFE_RESOLVE(val, ctx);
 
+	CallingClass = (PClass*)ctx.Class;
 	if (!val->ValueType->IsKindOf(RUNTIME_CLASS(PClassPointer)))
 	{
 		ScriptPosition.Message(MSG_ERROR, "Class type expected");
@@ -5058,6 +5060,7 @@ FxExpression *FxNew::Resolve(FCompileContext &ctx)
 		auto cls = static_cast<PClass *>(static_cast<FxConstant*>(val)->GetValue().GetPointer());
 		ValueType = NewPointer(cls);
 	}
+
 	return this;
 }
 
@@ -5072,7 +5075,7 @@ ExpEmit FxNew::Emit(VMFunctionBuilder *build)
 	ExpEmit from = val->Emit(build);
 	from.Free(build);
 	ExpEmit to(build, REGT_POINTER);
-	build->Emit(from.Konst ? OP_NEW_K : OP_NEW, to.RegNum, from.RegNum);
+	build->Emit(from.Konst ? OP_NEW_K : OP_NEW, to.RegNum, from.RegNum, build->GetConstantAddress(CallingClass, ATAG_OBJECT));
 	return to;
 }
 
@@ -7527,8 +7530,18 @@ FxExpression *FxFunctionCall::Resolve(FCompileContext& ctx)
 		break;
 
 	case NAME_New:
-		if (CheckArgSize(MethodName, ArgList, 1, 1, ScriptPosition))
+		if (CheckArgSize(MethodName, ArgList, 0, 1, ScriptPosition))
 		{
+			// [ZZ] allow implicit new() call to mean "create current class instance"
+			if (!ArgList.Size() && !ctx.Class->IsKindOf(RUNTIME_CLASS(PClass)))
+			{
+				ScriptPosition.Message(MSG_ERROR, "Cannot use implicit new() in a struct");
+				delete this;
+				return nullptr;
+			}
+			else if (!ArgList.Size())
+				ArgList.Push(new FxConstant((PClass*)ctx.Class, NewClassPointer((PClass*)ctx.Class), ScriptPosition));
+
 			func = new FxNew(ArgList[0]);
 			ArgList[0] = nullptr;
 		}
diff --git a/src/scripting/backend/codegen.h b/src/scripting/backend/codegen.h
index abbcbd54e3..90c4741706 100644
--- a/src/scripting/backend/codegen.h
+++ b/src/scripting/backend/codegen.h
@@ -1208,6 +1208,7 @@ private:
 class FxNew : public FxExpression
 {
 	FxExpression *val;
+	PClass *CallingClass;
 
 public:
 
diff --git a/src/scripting/vm/vmexec.h b/src/scripting/vm/vmexec.h
index 8da2c4d8d0..9f93af802e 100644
--- a/src/scripting/vm/vmexec.h
+++ b/src/scripting/vm/vmexec.h
@@ -787,7 +787,8 @@ begin:
 	{
 		b = B;
 		PClass *cls = (PClass*)(pc->op == OP_NEW ? reg.a[b] : konsta[b].v);
-		if (cls->ObjectFlags & OF_Abstract) ThrowAbortException(X_OTHER, "Cannot instantiate abstract class %s", cls->TypeName.GetChars());
+		PClass *callingcls = (PClass*)konsta[C].o; // [ZZ] due to how this is set, it's always const
+		if ((cls->ObjectFlags & OF_Abstract) && callingcls != cls) ThrowAbortException(X_OTHER, "Cannot instantiate abstract class %s outside of that class", cls->TypeName.GetChars());
 		reg.a[a] = cls->CreateNew();
 		reg.atag[a] = ATAG_OBJECT;
 		NEXTOP;