Test for Trac #1759

testsuite/tests/ghc-regress/deSugar/should_compile/all.T

@@ -65,3 +65,4 @@ test('ds058', normal, compile, ['-W'])
 test('ds059', normal, compile, ['-W'])
 test('ds060', expect_broken(322), compile, [''])
 test('ds061', expect_broken(851), compile, [''])
+test('ds062', normal, compile, [''])

testsuite/tests/ghc-regress/deSugar/should_compile/ds062.hs

+{-# OPTIONS_GHC -Wall #-}
+
+module ShouldCompile where
+
+f :: String -> Int
+f x | null x    = 1
+    | otherwise = 2
+
+-- Should not give a non-exhaustive-patterns error
+-- See Trac #1759
+