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`.

6 files changed, 92 insertions, 1 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'])
diff --git a/testsuite/tests/rename/should_fail/T15957_Fail.hs b/testsuite/tests/rename/should_fail/T15957_Fail.hs
new file mode 100644
index 0000000000..77ed3ada15
--- /dev/null
+++ b/testsuite/tests/rename/should_fail/T15957_Fail.hs
@@ -0,0 +1,32 @@
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE NamedFieldPuns #-}
+module T15957_Fail where
+
+data P = P { x :: Int, y :: Int }
+
+f1 P{..} = 1 + 3 -- nothing bound is used
+f2 P{x, ..} = x + 3 -- y bound but not used
+f3 P{x, y, ..} = x + y -- no bindings left, i.e. no new useful bindings introduced
+
+g2 P{x=a, ..} = a + 3
+g3 P{x=a, y=b, ..} = a + b
+g4 P{x=0, y=0,..} = 0
+g4 _ = 0
+
+-- 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 $ 0
+
+let_in_example :: Int
+let_in_example =
+  let P{..} = P 1 2
+  in 0
+
+data Q = Q { a, b :: P }
+
+nested :: Q -> Int
+nested Q { a = P{..}, .. } = (case b of (P x1 _) -> x1)
+
diff --git a/testsuite/tests/rename/should_fail/T15957_Fail.stderr b/testsuite/tests/rename/should_fail/T15957_Fail.stderr
new file mode 100644
index 0000000000..54d77c189b
--- /dev/null
+++ b/testsuite/tests/rename/should_fail/T15957_Fail.stderr
@@ -0,0 +1,36 @@
+
+T15957_Fail.hs:7:6: error: [-Wunused-record-wildcards (in -Wall), -Werror=unused-record-wildcards]
+    No variables bound in the record wildcard match are used
+      Possible fix: omit the ‘..’
+
+T15957_Fail.hs:8:9: error: [-Wunused-record-wildcards (in -Wall), -Werror=unused-record-wildcards]
+    No variables bound in the record wildcard match are used
+      Possible fix: omit the ‘..’
+
+T15957_Fail.hs:9:12: error: [-Wredundant-record-wildcards (in -Wall), -Werror=redundant-record-wildcards]
+    Record wildcard does not bind any new variables
+      Possible fix: omit the ‘..’
+
+T15957_Fail.hs:11:11: error: [-Wunused-record-wildcards (in -Wall), -Werror=unused-record-wildcards]
+    No variables bound in the record wildcard match are used
+      Possible fix: omit the ‘..’
+
+T15957_Fail.hs:12:16: error: [-Wredundant-record-wildcards (in -Wall), -Werror=redundant-record-wildcards]
+    Record wildcard does not bind any new variables
+      Possible fix: omit the ‘..’
+
+T15957_Fail.hs:13:15: error: [-Wredundant-record-wildcards (in -Wall), -Werror=redundant-record-wildcards]
+    Record wildcard does not bind any new variables
+      Possible fix: omit the ‘..’
+
+T15957_Fail.hs:20:9: error: [-Wunused-record-wildcards (in -Wall), -Werror=unused-record-wildcards]
+    No variables bound in the record wildcard match are used
+      Possible fix: omit the ‘..’
+
+T15957_Fail.hs:25:9: error: [-Wunused-record-wildcards (in -Wall), -Werror=unused-record-wildcards]
+    No variables bound in the record wildcard match are used
+      Possible fix: omit the ‘..’
+
+T15957_Fail.hs:31:18: error: [-Wunused-record-wildcards (in -Wall), -Werror=unused-record-wildcards]
+    No variables bound in the record wildcard match are used
+      Possible fix: omit the ‘..’
diff --git a/testsuite/tests/rename/should_fail/T9437.stderr b/testsuite/tests/rename/should_fail/T9437.stderr
index 8c2222ef97..2b8ec84502 100644
--- a/testsuite/tests/rename/should_fail/T9437.stderr
+++ b/testsuite/tests/rename/should_fail/T9437.stderr
@@ -1,2 +1,2 @@
 
-T9437.hs:8:12: You cannot use `..' in a record update
+T9437.hs:8:18: You cannot use `..' in a record update
diff --git a/testsuite/tests/rename/should_fail/all.T b/testsuite/tests/rename/should_fail/all.T
index ce8c5c9a13..af382b1a0c 100644
--- a/testsuite/tests/rename/should_fail/all.T
+++ b/testsuite/tests/rename/should_fail/all.T
@@ -145,3 +145,4 @@ test('T16002', normal, compile_fail, [''])
 test('T16114', normal, compile_fail, [''])
 test('T16116b', normal, compile_fail, [''])
 test('ExplicitForAllRules2', normal, compile_fail, [''])
+test('T15957_Fail', normal, compile_fail, ['-Werror -Wall -Wno-missing-signatures'])