Add -Werror=compat

Add a flag `-Werror=compat` to GHC which has the effect of `-Werror=x
-Werror=y ...`, where `x, y, ...` are warnings from the `-Wcompat`
option group.

Test Plan: ./validate

Reviewers: bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: #15278

Differential Revision: https://phabricator.haskell.org/D4860

2 files changed, 18 insertions, 4 deletions

diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index 485eb72942..fa210dcce9 100644
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -3522,10 +3522,7 @@ dynamic_flags_deps = [
  ++ map (mkFlag turnOff "fno-"      unSetGeneralFlag  ) fFlagsDeps
  ++ map (mkFlag turnOn  "W"         setWarningFlag    ) wWarningFlagsDeps
  ++ map (mkFlag turnOff "Wno-"      unSetWarningFlag  ) wWarningFlagsDeps
- ++ map (mkFlag turnOn  "Werror="   (\flag -> do {
-                                       ; setWarningFlag flag
-                                       ; setFatalWarningFlag flag }))
-                                                        wWarningFlagsDeps
+ ++ map (mkFlag turnOn  "Werror="   setWErrorFlag )     wWarningFlagsDeps
  ++ map (mkFlag turnOn  "Wwarn="     unSetFatalWarningFlag )
                                                         wWarningFlagsDeps
  ++ map (mkFlag turnOn  "Wno-error=" unSetFatalWarningFlag )
@@ -3537,6 +3534,12 @@ dynamic_flags_deps = [
  ++ [ (NotDeprecated, unrecognisedWarning "W"),
       (Deprecated,    unrecognisedWarning "fwarn-"),
       (Deprecated,    unrecognisedWarning "fno-warn-") ]
+ ++ [ make_ord_flag defFlag "Werror=compat"
+        (NoArg (mapM_ setWErrorFlag minusWcompatOpts))
+    , make_ord_flag defFlag "Wno-error=compat"
+        (NoArg (mapM_ unSetFatalWarningFlag minusWcompatOpts))
+    , make_ord_flag defFlag "Wwarn=compat"
+        (NoArg (mapM_ unSetFatalWarningFlag minusWcompatOpts)) ]
  ++ map (mkFlag turnOn  "f"         setExtensionFlag  ) fLangFlagsDeps
  ++ map (mkFlag turnOff "fno-"      unSetExtensionFlag) fLangFlagsDeps
  ++ map (mkFlag turnOn  "X"         setExtensionFlag  ) xFlagsDeps
@@ -4802,6 +4805,11 @@ setFatalWarningFlag, unSetFatalWarningFlag :: WarningFlag -> DynP ()
 setFatalWarningFlag   f = upd (\dfs -> wopt_set_fatal dfs f)
 unSetFatalWarningFlag f = upd (\dfs -> wopt_unset_fatal dfs f)
 
+setWErrorFlag :: WarningFlag -> DynP ()
+setWErrorFlag flag =
+  do { setWarningFlag flag
+     ; setFatalWarningFlag flag }
+
 --------------------------
 setExtensionFlag, unSetExtensionFlag :: LangExt.Extension -> DynP ()
 setExtensionFlag f = upd (setExtensionFlag' f)
diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst
index 7dc4a3b048..510b56ad80 100644
--- a/docs/users_guide/using-warnings.rst
+++ b/docs/users_guide/using-warnings.rst
@@ -151,6 +151,9 @@ to abort.
     Makes a specific warning into a fatal error. The warning will be enabled if
     it hasn't been enabled yet.
 
+    ``-Werror=compat`` has the same effect as ``-Werror=...`` for each warning
+    flag in the :ghc-flag:`-Wcompat` option group.
+
 .. ghc-flag:: -Wwarn
     :shortdesc: make warnings non-fatal
     :type: dynamic
@@ -172,6 +175,9 @@ to abort.
     Note that it doesn't fully negate the effects of ``-Werror=<wflag>`` - the
     warning will still be enabled.
 
+    ``-Wwarn=compat`` has the same effect as ``-Wwarn=...`` for each warning
+    flag in the :ghc-flag:`-Wcompat` option group.
+
 When a warning is emitted, the specific warning flag which controls
 it is shown.