Test Trac #2307

testsuite/tests/ghc-regress/typecheck/should_fail/T2307.hs

+{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies,
+              OverlappingInstances, UndecidableInstances,
+	      IncoherentInstances,
+              FlexibleInstances #-}
+
+-- Trac #2307
+
+module ShouldFail where
+
+ class C a b c | a -> b, a -> c
+ instance C Int (Maybe String) Float
+ instance C Int (Maybe Bool)   Double

testsuite/tests/ghc-regress/typecheck/should_fail/T2307.stderr

+
+T2307.hs:11:10:
+    Functional dependencies conflict between instance declarations:
+      instance [incoherent] C Int (Maybe String) Float
+        -- Defined at T2307.hs:11:10-35
+      instance [incoherent] C Int (Maybe Bool) Double
+        -- Defined at T2307.hs:12:10-36

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

@@ -193,3 +193,4 @@ test('tcfail201', normal, compile_fail, [''])
 
 test('T1899', normal, compile_fail, [''])
 test('T2126', normal, compile_fail, [''])
+test('T2307', normal, compile_fail, [''])