Fix #14990 (#14991)

* Fix #14990

* Add testcase

compiler/semtypes.nim

@@ -1402,8 +1402,8 @@ proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType =
                [s.name.s, s.kind.toHumanStr])
     return newOrPrevType(tyError, prev, c)
 
-  var t = s.typ
-  if t.kind in {tyCompositeTypeClass, tyAlias} and t.base.kind == tyGenericBody:
+  var t = s.typ.skipTypes({tyAlias})
+  if t.kind == tyCompositeTypeClass and t.base.kind == tyGenericBody:
     t = t.base
 
   result = newOrPrevType(tyGenericInvocation, prev, c)

tests/generics/tgenerics_issues.nim

@@ -849,3 +849,14 @@ discard getBar(fakeReadLine()) # no error
 discard getBar("hello, world") # no error
 
 echo intoFoos(fakeReadLine().split(' ')) # no error, works as expected
+
+
+# bug #14990
+type
+  Tile3 = Tile2
+  Tile2 = Tile
+  Tile[n] = object
+    a: n
+
+var a: Tile3[int]
+