fixes #12964 (#13027)

compiler/sigmatch.nim

@@ -1863,11 +1863,11 @@ proc implicitConv(kind: TNodeKind, f: PType, arg: PNode, m: TCandidate,
   result = newNodeI(kind, arg.info)
   if containsGenericType(f):
     if not m.hasFauxMatch:
-      result.typ = getInstantiatedType(c, arg, m, f)
+      result.typ = getInstantiatedType(c, arg, m, f).skipTypes({tySink})
     else:
       result.typ = errorType(c)
   else:
-    result.typ = f
+    result.typ = f.skipTypes({tySink})
   if result.typ == nil: internalError(c.graph.config, arg.info, "implicitConv")
   result.add c.graph.emptyNode
   result.add arg

tests/destructor/tarc.nim

@@ -100,4 +100,18 @@ mkManyLeaks()
 tsimpleClosureIterator()
 tleakingNewStmt()
 leakObjConstr()
+
+# bug #12964
+
+type
+  Token* = ref object of RootObj
+  Li* = ref object of Token
+
+proc bug12964*() =
+  var token = Li()
+  var tokens = @[Token()]
+  tokens.add token
+
+bug12964()
+
 echo getOccupiedMem() - startMem