fixes #12051

compiler/liftdestructors.nim

@@ -182,8 +182,16 @@ proc considerAsgnOrSink(c: var TLiftCtx; t: PType; body, x, y: PNode;
     body.add newAsgnCall(c.g, op, x, y)
     result = true
 
-proc addDestructorCall(c: var TLiftCtx; t: PType; body, x: PNode) =
+proc addDestructorCall(c: var TLiftCtx; orig: PType; body, x: PNode) =
+  let t = orig.skipTypes(abstractInst)
   var op = t.destructor
+
+  if op != nil and sfOverriden in op.flags:
+    if op.ast[genericParamsPos].kind != nkEmpty:
+      # patch generic destructor:
+      op = instantiateGeneric(c, op, t, t.typeInst)
+      t.attachedOps[attachedDestructor] = op
+
   if op == nil and useNoGc(c, t):
     op = produceSym(c.g, c.c, t, attachedDestructor, c.info)
     doAssert op != nil

compiler/seminst.nim

@@ -387,7 +387,7 @@ proc generateInstance(c: PContext, fn: PSym, pt: TIdTable,
     if c.inGenericContext == 0:
       instantiateBody(c, n, fn.typ.n, result, fn)
     sideEffectsCheck(c, result)
-    if result.magic != mSlice:
+    if result.magic notin {mSlice, mTypeOf}:
       # 'toOpenArray' is special and it is allowed to return 'openArray':
       paramsTypeCheck(c, result.typ)
   else:

tests/destructor/tnewruntime_misc.nim

@@ -4,7 +4,10 @@ discard """
 Indeed
 axc
 (v: 10)
-0  new: 0'''
+0  new: 0
+...
+destroying GenericObj[T] GenericObj[system.int]
+'''
 """
 
 import core / allocators
@@ -98,3 +101,19 @@ proc toTable[A,B](p: sink openArray[(A, B)]): Table[A, B] =
 
 
 let table = {"a": new(int)}.toTable()
+
+# bug # #12051
+
+type
+  GenericObj[T] = object
+    val: T
+  Generic[T] = owned ref GenericObj[T]
+
+proc `=destroy`[T](x: var GenericObj[T]) =
+  echo "destroying GenericObj[T] ", x.typeof # to know when its being destroyed
+
+proc main12() =
+  let gnrc = Generic[int](val: 42)
+  echo "..."
+
+main12()