fixes #18059 (#18140)

* fixes #18059

tests/metatype/tcps.nim

@@ -0,0 +1,35 @@
+discard """
+  output: '''10
+string'''
+"""
+
+# bug #18059
+type
+  C = ref object of RootObj
+    fn: ContProc
+    ex: ref Exception
+
+  ContProc = proc (c: C): C {.nimcall.}
+
+proc noop(c: C): C = c
+
+type
+  Env[T] = ref object of C
+    x: T
+
+proc foo_cont[U](c: C): C =
+  proc afterCall[V](c: C): C =
+    echo Env[V](c).x
+
+  c.fn = afterCall[U]
+  return noop(c)
+
+proc foo[T](x: T): C =
+  return Env[T](fn: foo_cont[T], x: x)
+
+proc tramp(c: sink C) =
+  while c != nil and c.fn != nil:
+    c = c.fn(c)
+
+tramp foo(10)
+tramp foo("string")