objects with no ancestor are not implicitely final

compiler/ast.nim

@@ -305,7 +305,7 @@ type
     tyBigNum, 
     tyConst, tyMutable, tyVarargs, 
     tyIter, # unused
-    tyProxy # currently unused
+    tyProxy # used as errornous type (for idetools)
     tyTypeClass,
 
 const
@@ -328,10 +328,11 @@ type
     nfSem       # node has been checked for semantics
 
   TNodeFlags* = set[TNodeFlag]
-  TTypeFlag* = enum   # keep below 15 for efficiency reasons (now: 13)
+  TTypeFlag* = enum   # keep below 15 for efficiency reasons (now: 14)
     tfVarargs,        # procedure has C styled varargs
     tfNoSideEffect,   # procedure type does not allow side effects
     tfFinal,          # is the object final?
+    tfInheritable,    # is the object inheritable?
     tfAcyclic,        # type is acyclic (for GC optimization)
     tfEnumHasHoles,   # enum cannot be mapped into a range
     tfShallow,        # type can be shallow copied on assignment

compiler/condsyms.nim

@@ -57,6 +57,7 @@ proc InitDefines*() =
   DefineSymbol("nimrod") # 'nimrod' is always defined
   # for bootstrapping purposes and old code:
   DefineSymbol("nimhygiene")
+  DefineSymbol("niminheritable")
   
   # add platform specific symbols:
   case targetCPU

compiler/pragmas.nim

@@ -48,7 +48,7 @@ const
   typePragmas* = {wImportc, wExportc, wDeprecated, wMagic, wAcyclic, wNodecl, 
     wPure, wHeader, wCompilerProc, wFinal, wSize, wExtern, wShallow, 
     wImportcpp, wImportobjc, wError, wIncompleteStruct, wByCopy, wByRef,
-    wGenSym, wInject}
+    wInheritable, wGenSym, wInject}
   fieldPragmas* = {wImportc, wExportc, wDeprecated, wExtern, 
     wImportcpp, wImportobjc, wError}
   varPragmas* = {wImportc, wExportc, wVolatile, wRegister, wThreadVar, wNodecl, 
@@ -584,7 +584,11 @@ proc pragma(c: PContext, sym: PSym, n: PNode, validPragmas: TSpecialWords) =
             noVal(it)
             if sym.typ == nil: invalidPragma(it)
             else: incl(sym.typ.flags, tfFinal)
-          of wAcyclic: 
+          of wInheritable:
+            noVal(it)
+            if sym.typ == nil or tfFinal in sym.typ.flags: invalidPragma(it)
+            else: incl(sym.typ.flags, tfInheritable)
+          of wAcyclic:
             noVal(it)
             if sym.typ == nil: invalidPragma(it)
             else: incl(sym.typ.flags, tfAcyclic)

compiler/semtypes.nim

@@ -545,6 +545,8 @@ proc semObjectNode(c: PContext, n: PNode, prev: PType): PType =
     var s = newSymS(skType, newIdentNode(getIdent("dummy"), n.info), c)
     s.typ = result
     pragma(c, s, n.sons[0], typePragmas)
+  if base == nil and tfInheritable notin result.flags:
+    incl(result.flags, tfFinal)
   
 proc addParamOrResult(c: PContext, param: PSym, kind: TSymKind) =
   if kind == skMacro and param.typ.kind in {tyTypeDesc, tyExpr, tyStmt}: