Implement -Wredundant-record-wildcards and -Wunused-record-wildcards

-Wredundant-record-wildcards warns when a .. pattern binds no variables.

-Wunused-record-wildcards warns when none of the variables bound by a ..
pattern are used.

These flags are enabled by `-Wall`.

2 files changed, 22 insertions, 0 deletions

diff --git a/testsuite/tests/rename/should_compile/T15957.hs b/testsuite/tests/rename/should_compile/T15957.hs
new file mode 100644
index 0000000000..d684e57495
--- /dev/null
+++ b/testsuite/tests/rename/should_compile/T15957.hs
@@ -0,0 +1,21 @@
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE NamedFieldPuns #-}
+module T15957 where
+
+data P = P { x :: Int, y :: Int }
+
+g1 P{..} = x + 3 -- x from .. is used
+g2 P{x, ..} = x + y -- y from .. is used, even if it's in a weird style
+
+old P{..} | x < 5 = 10
+
+-- Record wildcards in lets have different scoping rules.. they bring
+-- all the identifiers into scope
+do_example :: IO Int
+do_example = do
+  let P{..} = P 1 2
+  return $ x + y
+
+let_in_example =
+  let P{..} = P 1 2
+  in x + 4
diff --git a/testsuite/tests/rename/should_compile/all.T b/testsuite/tests/rename/should_compile/all.T
index 0c60360e17..4d427de44f 100644
--- a/testsuite/tests/rename/should_compile/all.T
+++ b/testsuite/tests/rename/should_compile/all.T
@@ -166,3 +166,4 @@ test('T15798a', normal, compile, [''])
 test('T15798b', normal, compile, [''])
 test('T15798c', normal, compile, [''])
 test('T16116a', normal, compile, [''])
+test('T15957', normal, compile, ['-Werror -Wredundant-record-wildcards -Wunused-record-wildcards'])