Test Trac #5300

tests/ghc-regress/typecheck/should_fail/T5300.hs

@@ -0,0 +1,15 @@
+{-# LANGUAGE FunctionalDependencies, MultiParamTypeClasses #-}
+module T5300 where
+
+import Control.Monad.State (StateT)
+
+class C1 a b c | a -> b
+class C2 a b c
+
+data T b = T
+
+f1 :: (Monad m, C1 a b c) => a -> StateT (T b) m a
+f1 f = undefined
+
+f2 :: (Monad m, C1 a1 b1 c1, C2 a2 b2 c2) => a1 -> StateT (T b2) m a2
+f2 fm = f1 fm >>= return . undefined

tests/ghc-regress/typecheck/should_fail/T5300.stderr

@@ -0,0 +1,8 @@
+
+T5300.hs:15:9:
+    Ambiguous type variable `c0' in the constraint:
+      (C1 a1 b2 c0) arising from a use of `f1'
+    Probable fix: add a type signature that fixes these type variable(s)
+    In the first argument of `(>>=)', namely `f1 fm'
+    In the expression: f1 fm >>= return . undefined
+    In an equation for `f2': f2 fm = f1 fm >>= return . undefined

tests/ghc-regress/typecheck/should_fail/all.T

@@ -242,3 +242,4 @@ test('FailDueToGivenOverlapping', normal, compile_fail, [''])
 test('LongWayOverlapping', normal, compile_fail, [''])
 test('T5236',normal,compile_fail,[''])
 test('T5246',normal,compile_fail,[''])
+test('T5300',normal,compile_fail,[''])