Add -Wcompat warning flag group

Reviewers: hvr, austin, thomie, bgamari

Reviewed By: hvr, austin, thomie, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1495

GHC Trac Issues: #11000

6 files changed, 73 insertions, 0 deletions

diff --git a/testsuite/tests/wcompat-warnings/WCompatWarningsNotOn.hs b/testsuite/tests/wcompat-warnings/WCompatWarningsNotOn.hs
new file mode 100644
index 0000000000..2f86d46bc2
--- /dev/null
+++ b/testsuite/tests/wcompat-warnings/WCompatWarningsNotOn.hs
@@ -0,0 +1,12 @@
+-- Test purpose:
+-- Ensure that not using -Wcompat does not enable its warnings
+
+-- {-# OPTIONS_GHC -Wcompat #-}
+-- {-# OPTIONS_GHC -Wno-compat #-}
+
+module WCompatWarningsNotOn where
+
+monadFail :: Monad m => m a
+monadFail = do
+    Just _ <- undefined
+    undefined
diff --git a/testsuite/tests/wcompat-warnings/WCompatWarningsOff.hs b/testsuite/tests/wcompat-warnings/WCompatWarningsOff.hs
new file mode 100644
index 0000000000..727a4e7600
--- /dev/null
+++ b/testsuite/tests/wcompat-warnings/WCompatWarningsOff.hs
@@ -0,0 +1,12 @@
+-- Test purpose:
+-- Ensure that using -Wno-compat does not switch on warnings
+
+-- {-# OPTIONS_GHC -Wcompat #-}
+{-# OPTIONS_GHC -Wno-compat #-}
+
+module WCompatWarningsOff where
+
+monadFail :: Monad m => m a
+monadFail = do
+    Just _ <- undefined
+    undefined
diff --git a/testsuite/tests/wcompat-warnings/WCompatWarningsOn.hs b/testsuite/tests/wcompat-warnings/WCompatWarningsOn.hs
new file mode 100644
index 0000000000..29fcc9eeb3
--- /dev/null
+++ b/testsuite/tests/wcompat-warnings/WCompatWarningsOn.hs
@@ -0,0 +1,12 @@
+-- Test purpose:
+-- Ensure that -Wcompat switches on the right warnings
+
+{-# OPTIONS_GHC -Wcompat #-}
+-- {-# OPTIONS_GHC -Wno-compat #-}
+
+module WCompatWarningsOn where
+
+monadFail :: Monad m => m a
+monadFail = do
+    Just _ <- undefined
+    undefined
diff --git a/testsuite/tests/wcompat-warnings/WCompatWarningsOn.stderr b/testsuite/tests/wcompat-warnings/WCompatWarningsOn.stderr
new file mode 100644
index 0000000000..03fc4e26c1
--- /dev/null
+++ b/testsuite/tests/wcompat-warnings/WCompatWarningsOn.stderr
@@ -0,0 +1,21 @@
+
+WCompatWarningsOn.hs:11:5: warning:
+    Could not deduce (MonadFail m)
+      arising from the failable pattern ‘Just _’
+      (this will become an error a future GHC release)
+    from the context: Monad m
+      bound by the type signature for:
+                 monadFail :: Monad m => m a
+      at WCompatWarningsOn.hs:9:14-27
+    Possible fix:
+      add (MonadFail m) to the context of
+        the type signature for:
+          monadFail :: Monad m => m a
+    In a stmt of a 'do' block: Just _ <- undefined
+    In the expression:
+      do { Just _ <- undefined;
+           undefined }
+    In an equation for ‘monadFail’:
+        monadFail
+          = do { Just _ <- undefined;
+                 undefined }
diff --git a/testsuite/tests/wcompat-warnings/WCompatWarningsOnOff.hs b/testsuite/tests/wcompat-warnings/WCompatWarningsOnOff.hs
new file mode 100644
index 0000000000..26d3973702
--- /dev/null
+++ b/testsuite/tests/wcompat-warnings/WCompatWarningsOnOff.hs
@@ -0,0 +1,12 @@
+-- Test purpose:
+-- Ensure that -Wno-compat disables a previously set -Wcompat
+
+{-# OPTIONS_GHC -Wcompat #-}
+{-# OPTIONS_GHC -Wno-compat #-}
+
+module WCompatWarningsOnOff where
+
+monadFail :: Monad m => m a
+monadFail = do
+    Just _ <- undefined
+    undefined
diff --git a/testsuite/tests/wcompat-warnings/all.T b/testsuite/tests/wcompat-warnings/all.T
new file mode 100644
index 0000000000..4447f994cb
--- /dev/null
+++ b/testsuite/tests/wcompat-warnings/all.T
@@ -0,0 +1,4 @@
+test('WCompatWarningsOn',    normal, compile, [''])
+test('WCompatWarningsOff',   normal, compile, [''])
+test('WCompatWarningsNotOn', normal, compile, [''])
+test('WCompatWarningsOnOff', normal, compile, [''])