Print which warning-flag controls an emitted warning.wip/D1934

Summary:
Both gcc and clang tell which warning flag a reported warning can be
controlled with, this patch makes ghc do the same. More generally, this
allows for annotated compiler output, where an optional annotation is
displayed in brackets after the severity.

Fixes T10752.

Reviewers: austin, hvr, goldfire, bgamari

Subscribers: goldfire, thomie

Differential Revision: https://phabricator.haskell.org/D1934

1 files changed, 12 insertions, 8 deletions

diff --git a/compiler/rename/RnEnv.hs b/compiler/rename/RnEnv.hs
index 5d74d7c94f..4f832f8443 100644
--- a/compiler/rename/RnEnv.hs
+++ b/compiler/rename/RnEnv.hs
@@ -743,7 +743,8 @@ lookup_demoted rdr_name dflags
            Just demoted_name
              | data_kinds ->
              do { whenWOptM Opt_WarnUntickedPromotedConstructors $
-                  addWarn (untickedPromConstrWarn demoted_name)
+                  addWarn Opt_WarnUntickedPromotedConstructors
+                          (untickedPromConstrWarn demoted_name)
                 ; return demoted_name }
              | otherwise  -> unboundNameX WL_Any rdr_name suggest_dk }
 
@@ -1068,7 +1069,8 @@ warnIfDeprecated gre@(GRE { gre_name = name, gre_imp = iss })
                    -- See Note [Handling of deprecations]
          do { iface <- loadInterfaceForName doc name
             ; case lookupImpDeprec iface gre of
-                Just txt -> addWarn (mk_msg imp_spec txt)
+                Just txt -> addWarn Opt_WarnWarningsDeprecations
+                           (mk_msg imp_spec txt)
                 Nothing  -> return () } }
   | otherwise
   = return ()
@@ -1738,7 +1740,8 @@ checkShadowedOccs (global_env,local_env) get_loc_occ ns
                 -- we don't find any GREs that are in scope qualified-only
 
           complain []      = return ()
-          complain pp_locs = addWarnAt loc (shadowedNameWarn occ pp_locs)
+          complain pp_locs = addWarnAt Opt_WarnNameShadowing
+                                 loc (shadowedNameWarn occ pp_locs)
 
     is_shadowed_gre :: GlobalRdrElt -> RnM Bool
         -- Returns False for record selectors that are shadowed, when
@@ -2118,7 +2121,8 @@ warnUnusedLocals names = do
 warnUnusedLocal :: NameEnv (FieldLabelString, Name) -> Name -> RnM ()
 warnUnusedLocal fld_env name
   = when (reportable name) $
-    addUnusedWarning occ (nameSrcSpan name)
+    addUnusedWarning Opt_WarnUnusedLocalBinds
+                     occ (nameSrcSpan name)
                      (text "Defined but not used")
   where
     occ = case lookupNameEnv fld_env name of
@@ -2132,7 +2136,7 @@ warnUnusedGRE gre@(GRE { gre_name = name, gre_lcl = lcl, gre_imp = is })
   | otherwise = when (reportable name) (mapM_ warn is)
   where
     occ = greOccName gre
-    warn spec = addUnusedWarning occ span msg
+    warn spec = addUnusedWarning Opt_WarnUnusedTopBinds occ span msg
         where
            span = importSpecLoc spec
            pp_mod = quotes (ppr (importSpecModule spec))
@@ -2154,9 +2158,9 @@ reportable name
                                   -- from Data.Tuple
   | otherwise = not (startsWithUnderscore (nameOccName name))
 
-addUnusedWarning :: OccName -> SrcSpan -> SDoc -> RnM ()
-addUnusedWarning occ span msg
-  = addWarnAt span $
+addUnusedWarning :: WarningFlag -> OccName -> SrcSpan -> SDoc -> RnM ()
+addUnusedWarning flag occ span msg
+  = addWarnAt flag span $
     sep [msg <> colon,
          nest 2 $ pprNonVarNameSpace (occNameSpace occ)
                         <+> quotes (ppr occ)]