Test Trac #8392

5 files changed, 34 insertions, 0 deletions

diff --git a/testsuite/tests/typecheck/should_compile/T8392.hs b/testsuite/tests/typecheck/should_compile/T8392.hs
new file mode 100644
index 0000000000..d86d29b8bc
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T8392.hs
@@ -0,0 +1,17 @@
+{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, ScopedTypeVariables, TypeFamilies, UndecidableInstances, AllowAmbiguousTypes #-}
+
+module T8392 where
+
+class Fun f a b where
+    fun :: f -> a -> b
+
+instance (b ~ Int, a ~ Int) => Fun F a b
+    where fun _ = (+1)
+
+data F = F
+
+data Compose a b = Compose a b
+
+-- ghc-7.6 version
+instance (Fun f b c, Fun g a b) => Fun (Compose f g) a c where
+    fun (Compose f g) a = fun f (fun g a :: b)
\ No newline at end of file
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index eb0e934220..0ccd90a35e 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -410,3 +410,4 @@ test('T7891', normal, compile, [''])
 test('T7903', normal, compile, [''])
 test('TcTypeNatSimple', normal, compile, [''])
 test('TcCoercibleCompile', when(compiler_lt('ghc', '7.7'), skip), compile, [''])
+test('T8392', normal, compile, [''])
diff --git a/testsuite/tests/typecheck/should_fail/T8392a.hs b/testsuite/tests/typecheck/should_fail/T8392a.hs
new file mode 100644
index 0000000000..6f47b4e331
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T8392a.hs
@@ -0,0 +1,7 @@
+{-# LANGUAGE GADTs, AllowAmbiguousTypes #-}
+module T8392a where
+
+-- Should complain even with AllowAmbiguousTypes
+
+foo :: (Int ~ Bool) => a -> a
+foo x = x
diff --git a/testsuite/tests/typecheck/should_fail/T8392a.stderr b/testsuite/tests/typecheck/should_fail/T8392a.stderr
new file mode 100644
index 0000000000..6e102227cf
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T8392a.stderr
@@ -0,0 +1,7 @@
+
+T8392a.hs:6:8:
+    Couldn't match type ‛Int’ with ‛Bool’
+    Inaccessible code in
+      the type signature for foo :: Int ~ Bool => a -> a
+    In the ambiguity check for: forall a. Int ~ Bool => a -> a
+    In the type signature for ‛foo’: foo :: Int ~ Bool => a -> a
diff --git a/testsuite/tests/typecheck/should_fail/all.T b/testsuite/tests/typecheck/should_fail/all.T
index cac7d92a13..bf11f6c94b 100644
--- a/testsuite/tests/typecheck/should_fail/all.T
+++ b/testsuite/tests/typecheck/should_fail/all.T
@@ -320,3 +320,5 @@ test('TcCoercibleFail', when(compiler_lt('ghc', '7.7'), skip), compile_fail, [''
 test('TcCoercibleFailSafe', when(compiler_lt('ghc', '7.7'), skip), compile_fail, [''])
 test('TcCoercibleFail2', when(compiler_lt('ghc', '7.7'), skip), compile_fail, [''])
 test('T8306', normal, compile_fail, [''])
+test('T8392a', normal, compile_fail, [''])
+