attempt to fix #5621 #5615 generic ref object typeRel (#5633)

compiler/semtypinst.nim

@@ -472,7 +472,7 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
           var r = replaceTypeVarsT(cl, result.sons[i])
           if result.kind == tyObject:
             # carefully coded to not skip the precious tyGenericInst:
-            let r2 = r.skipTypes({tyGenericInst, tyAlias})
+            let r2 = r.skipTypes({tyAlias})
             if r2.kind in {tyPtr, tyRef}:
               r = skipTypes(r2, {tyPtr, tyRef})
           result.sons[i] = r

tests/generics/tobjecttyperel2.nim

@@ -0,0 +1,42 @@
+discard """
+  output: '''1
+a
+13'''
+"""
+
+# bug #5621 #5615
+type
+  Obj5[T] = ref object of RootObj
+    x_impl: T
+
+proc x[T](v476205: Obj5[T]): T {.used.} =
+  v476205.x_impl
+
+type
+  Obj6[T, U] = ref object of Obj5[T]
+    y_impl: U
+
+proc newObj6[T, U](x: T; y: U): Obj6[T, U] =
+  new(result)
+  result.x_impl = x
+  result.y_impl = y
+
+proc x[T, U](v477606: Obj6[T, U]): T {.used.} =
+  v477606.x_impl
+
+proc y[T, U](v477608: Obj6[T, U]): U {.used.} =
+  v477608.y_impl
+
+let e = newObj6(1, "a")
+echo e.x
+echo e.y
+
+type
+  Fruit[T] = ref object of RootObj
+  Apple[T] = ref object of Fruit[T]
+
+proc getColor[T](v: Fruit[T]): T = 13
+
+var w: Apple[int]
+let r = getColor(w)
+echo r