Elaborate test for Trac #10403

testsuite/tests/partial-sigs/should_compile/T10403.hs

 {-# LANGUAGE PartialTypeSignatures #-}
+{-# OPTIONS_GHC -fdefer-type-errors #-}
 module T10403 where
 
 data I a = I a
@@ -11,9 +12,10 @@ instance Functor (B t) where
 
 newtype H f = H (f ())
 
-app :: H (B t)
-app = h (H . I) (B ())
-
 h :: _ => _
---h :: Functor m => (a -> b) -> m a -> H m
+-- h :: Functor m => (a -> b) -> m a -> H m
 h f b = (H . fmap (const ())) (fmap f b)
+
+h2 :: _
+-- h2 :: Functor m => (a -> b) -> m a -> H m
+h2 f b = (H . fmap (const ())) (fmap f b)

testsuite/tests/partial-sigs/should_compile/T10403.stderr

-
-T10403.hs:17:6: warning:
-    Found hole ‘_’ with inferred constraints: Functor f
-    In the type signature for ‘h’: _ => _
-
-T10403.hs:17:11: warning:
-    Found hole ‘_’ with type: (a -> b) -> f a -> H f
-    Where: ‘f’ is a rigid type variable bound by
-               the inferred type of h :: Functor f => (a -> b) -> f a -> H f
-               at T10403.hs:19:1
-           ‘b’ is a rigid type variable bound by
-               the inferred type of h :: Functor f => (a -> b) -> f a -> H f
-               at T10403.hs:19:1
-           ‘a’ is a rigid type variable bound by
-               the inferred type of h :: Functor f => (a -> b) -> f a -> H f
-               at T10403.hs:19:1
-    In the type signature for ‘h’: _ => _
+
+T10403.hs:15:6: warning:
+    Found hole ‘_’ with inferred constraints: Functor f
+    In the type signature for ‘h’: _ => _
+
+T10403.hs:15:11: warning:
+    Found hole ‘_’ with type: (a -> b) -> f a -> H f
+    Where: ‘f’ is a rigid type variable bound by
+               the inferred type of h :: Functor f => (a -> b) -> f a -> H f
+               at T10403.hs:17:1
+           ‘b’ is a rigid type variable bound by
+               the inferred type of h :: Functor f => (a -> b) -> f a -> H f
+               at T10403.hs:17:1
+           ‘a’ is a rigid type variable bound by
+               the inferred type of h :: Functor f => (a -> b) -> f a -> H f
+               at T10403.hs:17:1
+    In the type signature for ‘h’: _ => _
+
+T10403.hs:19:7: warning:
+    Found hole ‘_’ with type: (a -> b) -> f a -> H f
+    Where: ‘f’ is a rigid type variable bound by
+               the inferred type of h2 :: Functor f => (a -> b) -> f a -> H f
+               at T10403.hs:21:1
+           ‘b’ is a rigid type variable bound by
+               the inferred type of h2 :: Functor f => (a -> b) -> f a -> H f
+               at T10403.hs:21:1
+           ‘a’ is a rigid type variable bound by
+               the inferred type of h2 :: Functor f => (a -> b) -> f a -> H f
+               at T10403.hs:21:1
+    In the type signature for ‘h2’: _
+
+T10403.hs:21:1: warning:
+    No instance for (Functor f)
+    When checking that ‘h2’ has the inferred type
+      h2 :: forall (f :: * -> *) b a. (a -> b) -> f a -> H f
+    Probable cause: the inferred type is ambiguous