Implement basic uniform warning set tower

This implements/completes the current basic warning sets to provide the
following tower of warning sets (i.e. each line subsumes the warnings
from the sets listed below):

- `-Weverything`
- `-Wall`
- `-Wextra` (alias of `-W`)
- `-Wdefault`

So for each of flags there's also a complement `-Wno-...` flag, which
subtracts the given set from the current enabled-warnings state.

Thus, we can now easily perform simple set subtraction operations, as
warning flags are evaluated from left-to-right on the command line.

So e.g.

- `-Weverything -Wno-all -Wno-compat` enables *all* warnings not enabled
  by `-Wall` and `-Wcompat`.

- `-Wextra -Wno-default` only warnings that `-Wextra` provides
  beyond the default warnings.

Reviewers: quchen, austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1850

1 files changed, 24 insertions, 4 deletions

diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index b86d1a7958..4b4eb77295 100644
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -2579,13 +2579,29 @@ dynamic_flags = [
   , defFlag "W"       (NoArg (mapM_ setWarningFlag minusWOpts))
   , defFlag "Werror"  (NoArg (setGeneralFlag           Opt_WarnIsError))
   , defFlag "Wwarn"   (NoArg (unSetGeneralFlag         Opt_WarnIsError))
-  , defFlag "Wcompat" (NoArg (mapM_ setWarningFlag minusWcompatOpts))
-  , defFlag "Wno-compat" (NoArg (mapM_ unSetWarningFlag minusWcompatOpts))
-  , defFlag "Wall"    (NoArg (mapM_ setWarningFlag minusWallOpts))
   , defFlag "Wnot"    (NoArg (do upd (\dfs -> dfs {warningFlags = IntSet.empty})
-                                 deprecate "Use -w instead"))
+                                 deprecate "Use -w or -Wno-everything instead"))
   , defFlag "w"       (NoArg (upd (\dfs -> dfs {warningFlags = IntSet.empty})))
 
+     -- New-style uniform warning sets
+     --
+     -- Note that -Weverything > -Wall > -Wextra > -Wdefault > -Wno-everything
+  , defFlag "Weverything"    (NoArg (mapM_ setWarningFlag minusWeverythingOpts))
+  , defFlag "Wno-everything"
+                      (NoArg (upd (\dfs -> dfs {warningFlags = IntSet.empty})))
+
+  , defFlag "Wall"           (NoArg (mapM_ setWarningFlag minusWallOpts))
+  , defFlag "Wno-all"        (NoArg (mapM_ unSetWarningFlag minusWallOpts))
+
+  , defFlag "Wextra"         (NoArg (mapM_ setWarningFlag minusWOpts))
+  , defFlag "Wno-extra"      (NoArg (mapM_ unSetWarningFlag minusWOpts))
+
+  , defFlag "Wdefault"       (NoArg (mapM_ setWarningFlag standardWarnings))
+  , defFlag "Wno-default"    (NoArg (mapM_ unSetWarningFlag standardWarnings))
+
+  , defFlag "Wcompat" (NoArg (mapM_ setWarningFlag minusWcompatOpts))
+  , defFlag "Wno-compat" (NoArg (mapM_ unSetWarningFlag minusWcompatOpts))
+
         ------ Plugin flags ------------------------------------------------
   , defGhcFlag "fplugin-opt" (hasArg addPluginModuleNameOption)
   , defGhcFlag "fplugin"     (hasArg addPluginModuleName)
@@ -3540,6 +3556,10 @@ minusWallOpts
         Opt_WarnMissingPatSynSigs
       ]
 
+-- | Things you get with -Weverything, i.e. *all* known warnings flags
+minusWeverythingOpts :: [WarningFlag]
+minusWeverythingOpts = [ toEnum 0 .. ]
+
 -- | Things you get with -Wcompat.
 --
 -- This is intended to group together warnings that will be enabled by default