Test Trac #12081

testsuite/tests/dependent/should_fail/T12081.hs

+{-# LANGUAGE TypeInType #-}
+
+module T12081 where
+
+data Nat = Z | S Nat
+
+class C (n :: Nat) where
+  type T n :: Nat
+  f :: (a :: T n)

testsuite/tests/dependent/should_fail/T12081.stderr

+
+T12081.hs:9:14: error:
+    • Type constructor ‘T’ cannot be used here
+        (it is defined and used in the same recursive group)
+    • In the kind ‘T n’
+      In the type signature: f :: (a :: T n)
+      In the class declaration for ‘C’

testsuite/tests/dependent/should_fail/all.T

@@ -15,3 +15,4 @@ test('KindLevelsB', normal, compile_fail, [''])
 test('T11473', normal, compile_fail, [''])
 test('T11471', normal, compile_fail, [''])
 test('T12174', normal, compile_fail, [''])
+test('T12081', normal, compile_fail, [''])