Test Trac #8889

(cherry picked from commit 0e2155dd)

testsuite/tests/indexed-types/should_compile/T8889.hs

+{-# LANGUAGE TypeFamilies, ConstraintKinds #-}
+{-# OPTIONS_GHC -fwarn-missing-signatures #-}  -- Report f's inferred type
+
+module T8889 where
+
+import GHC.Exts
+
+class C f where
+  type C_fmap f a :: Constraint
+  foo :: C_fmap f a => (a -> b) -> f a -> f b
+
+f x = foo x

testsuite/tests/indexed-types/should_compile/T8889.stderr

+
+T8889.hs:12:1: Warning:
+    Top-level binding with no type signature:
+      f :: forall (f :: * -> *) a b.
+           (C_fmap f a, C f) =>
+           (a -> b) -> f a -> f b

testsuite/tests/indexed-types/should_compile/all.T

@@ -239,3 +239,4 @@ test('ClosedFam1', extra_clean(['ClosedFam1.o-boot', 'ClosedFam1.hi-boot']),
 test('ClosedFam2', extra_clean(['ClosedFam2.o-boot', 'ClosedFam2.hi-boot']),
      multimod_compile, ['ClosedFam2', '-v0'])
 test('T8651', normal, compile, [''])
+test('T8889', normal, compile, [''])