Using separate keyword 'nonew' as reverse abstract; nonew is inherited, and nonew class can only be created from the first nonew class in the hierarchy

src/dobject.h

@@ -205,7 +205,8 @@ 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 new() function
+	OF_Abstract			= 1 << 14,		// Marks a class that cannot be created with new() function at all
+	OF_NoNew			= 1 << 15,		// Marks a class that can only be created with new() in the exact class that has this keyword
 };
 
 template<class T> class TObjPtr;

src/sc_man_scanner.re

@@ -170,6 +170,7 @@ std2:
 		'virtual'					{ RET(TK_Virtual); }
 		'override'					{ RET(TK_Override); }
 		'vararg'					{ RET(TK_VarArg); }
+		'nonew'						{ RET(TK_NoNew); }
 		'super'						{ RET(TK_Super); }
 		'global'					{ RET(TK_Global); }
 		'stop'						{ RET(TK_Stop); }

src/sc_man_tokens.h

@@ -112,6 +112,7 @@ xx(TK_Optional,				"'optional'")
 xx(TK_Export,				"'expert'")
 xx(TK_Virtual,				"'virtual'")
 xx(TK_VarArg,               "'vararg'")
+xx(TK_NoNew, 				"'nonew'")
 xx(TK_Override,				"'override'")
 xx(TK_Super,				"'super'")
 xx(TK_Null,					"'null'")

src/scripting/backend/codegen.cpp

@@ -5058,13 +5058,26 @@ FxExpression *FxNew::Resolve(FCompileContext &ctx)
 	if (val->isConstant())
 	{
 		auto cls = static_cast<PClass *>(static_cast<FxConstant*>(val)->GetValue().GetPointer());
-		if ((cls->ObjectFlags & OF_Abstract) && cls != ctx.Class)
+		if (cls->ObjectFlags & OF_Abstract)
 		{
-			ScriptPosition.Message(MSG_ERROR, "Cannot instantiate abstract class %s outside of that class", cls->TypeName.GetChars());
+			ScriptPosition.Message(MSG_ERROR, "Cannot instantiate abstract class %s", cls->TypeName.GetChars());
 			delete this;
 			return nullptr;
 		}
 
+		if (cls->ObjectFlags & OF_NoNew)
+		{
+			PClass* pcls = cls;
+			while (pcls && pcls->ParentClass && (pcls->ParentClass->ObjectFlags & OF_NoNew))
+				pcls = pcls->ParentClass;
+			if (pcls != ctx.Class)
+			{
+				ScriptPosition.Message(MSG_ERROR, "Cannot instantiate class %s directly", cls->TypeName.GetChars());
+				delete this;
+				return nullptr;
+			}
+		}
+
 		ValueType = NewPointer(cls);
 	}
 

src/scripting/vm/vmexec.h

@@ -788,7 +788,19 @@ begin:
 		b = B;
 		PClass *cls = (PClass*)(pc->op == OP_NEW ? reg.a[b] : konsta[b].v);
 		PFunction *callingfunc = (PFunction*)konsta[C].o; // [ZZ] due to how this is set, it's always const
-		if ((cls->ObjectFlags & OF_Abstract) && (!callingfunc || callingfunc->OwningClass != cls)) ThrowAbortException(X_OTHER, "Cannot instantiate abstract class %s outside of that class", cls->TypeName.GetChars());
+		if (cls->ObjectFlags & OF_Abstract) ThrowAbortException(X_OTHER, "Cannot instantiate abstract class %s", cls->TypeName.GetChars());
+		if (cls->ObjectFlags & OF_NoNew)
+		{
+			// trace to the first nonew class in the hierarchy.
+			// compare that class to the context class.
+			// if not matching, disallow creation.
+			// this ensures that only the root class can have a static factory method that can also create instances of subclasses via new().
+			PClass* pcls = cls;
+			while (pcls && pcls->ParentClass && (pcls->ParentClass->ObjectFlags & OF_NoNew))
+				pcls = pcls->ParentClass;
+			if (!callingfunc || pcls != callingfunc->OwningClass)
+				ThrowAbortException(X_OTHER, "Cannot instantiate class %s directly", cls->TypeName.GetChars());
+		}
 		reg.a[a] = cls->CreateNew();
 		reg.atag[a] = ATAG_OBJECT;
 		NEXTOP;

src/scripting/zscript/zcc-parse.lemon

@@ -212,6 +212,7 @@ class_ancestry(X) ::= COLON dottable_id(A).	{ X = A; /*X-overwrites-A*/ }
 %type class_flags{ClassFlagsBlock}
 class_flags(X) ::= .										{ X.Flags = 0; X.Replaces = NULL; }
 class_flags(X) ::= class_flags(A) ABSTRACT.					{ X.Flags = A.Flags | ZCC_Abstract; X.Replaces = A.Replaces; }
+class_flags(X) ::= class_flags(A) NONEW.					{ X.Flags = A.Flags | ZCC_NoNew; X.Replaces = A.Replaces; }
 class_flags(X) ::= class_flags(A) NATIVE.					{ X.Flags = A.Flags | ZCC_Native; X.Replaces = A.Replaces; }
 class_flags(X) ::= class_flags(A) REPLACES dottable_id(B).	{ X.Flags = A.Flags; X.Replaces = B; }
 

src/scripting/zscript/zcc_compile.cpp

@@ -599,9 +599,11 @@ void ZCCCompiler::CreateClassTypes()
 					}
 				}
 				if (c->Type() == nullptr) c->cls->Type = parent->FindClassTentative(c->NodeName());
-				// [ZZ] if parent class is abstract, this one should be abstract as well - otherwise we can subclass Actor and be able to new() our subclass
-				if ((c->cls->Flags & ZCC_Abstract) || (parent && parent->ObjectFlags & OF_Abstract))
+				if (c->cls->Flags & ZCC_Abstract)
 					c->Type()->ObjectFlags |= OF_Abstract;
+				// [ZZ] inherit nonew keyword
+				if (c->cls->Flags & ZCC_NoNew || (parent && parent->ObjectFlags & OF_NoNew))
+					c->Type()->ObjectFlags |= OF_NoNew;
 				c->Type()->bExported = true;	// this class is accessible to script side type casts. (The reason for this flag is that types like PInt need to be skipped.)
 				c->cls->Symbol = new PSymbolType(c->NodeName(), c->Type());
 				OutNamespace->Symbols.AddSymbol(c->cls->Symbol);

src/scripting/zscript/zcc_parser.cpp

@@ -137,6 +137,7 @@ static void InitTokenMap()
 	TOKENDEF (TK_Latent,		ZCC_LATENT);
 	TOKENDEF (TK_Virtual,		ZCC_VIRTUAL);
 	TOKENDEF (TK_VarArg,        ZCC_VARARG);
+	TOKENDEF (TK_NoNew, 		ZCC_NONEW);
 	TOKENDEF (TK_Override,		ZCC_OVERRIDE);
 	TOKENDEF (TK_Final,			ZCC_FINAL);
 	TOKENDEF (TK_Meta,			ZCC_META);

src/scripting/zscript/zcc_parser.h

@@ -36,7 +36,8 @@ enum
 	ZCC_Virtual			= 1 << 13,
 	ZCC_Override		= 1 << 14,
 	ZCC_Transient		= 1 << 15,
-	ZCC_VarArg			= 1 << 16
+	ZCC_VarArg			= 1 << 16,
+	ZCC_NoNew			= 1 << 17,
 };
 
 // Function parameter modifiers