Add tests for incomplete-pattern warnings

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

@@ -62,3 +62,4 @@ test('ds055', only_compiler_types(['ghc']), compile, [''])
 test('ds056', normal, compile, ['-Wall'])
 test('ds057', normal, compile, [''])
 test('ds058', normal, compile, ['-W'])
+test('ds059', normal, compile, ['-W'])

testsuite/tests/ghc-regress/deSugar/should_compile/ds059.hs

+{-# OPTIONS -fwarn-incomplete-patterns #-}
+
+-- Test for incomplete-pattern warnings
+-- None should cause a warning
+
+module ShouldCompile where
+
+-- These ones gave bogus warnings in 6.2
+
+data D = D1 { f1 :: Int } | D2
+
+-- Use pattern matching in the argument
+f :: D -> D
+f  d1@(D1 {f1 = n}) = d1 { f1 = f1 d1 + n } -- Warning here
+f  d = d
+
+-- Use case pattern matching
+g :: D -> D
+g  d1 = case d1 of
+           D1 { f1 = n } -> d1 { f1 = n + 1 } -- Warning here also
+           D2            -> d1
+
+-- These ones were from Neil Mitchell
+-- no warning
+ex1 x = ss
+    where (_s:ss) = x
+
+-- no warning
+ex2 x = let (_s:ss) = x in ss
+
+--    Warning: Pattern match(es) are non-exhaustive
+--             In a case alternative: Patterns not matched: []
+ex3 x = case x of ~(_s:ss) -> ss