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

40 files changed, 283 insertions, 182 deletions

diff --git a/compiler/coreSyn/CoreLint.hs b/compiler/coreSyn/CoreLint.hs
index 6dbcbe4ce9..c046e74089 100644
--- a/compiler/coreSyn/CoreLint.hs
+++ b/compiler/coreSyn/CoreLint.hs
@@ -284,7 +284,7 @@ displayLintResults :: DynFlags -> CoreToDo
                    -> IO ()
 displayLintResults dflags pass warns errs binds
   | not (isEmptyBag errs)
-  = do { log_action dflags dflags Err.SevDump noSrcSpan defaultDumpStyle
+  = do { log_action dflags dflags Nothing Err.SevDump noSrcSpan defaultDumpStyle
            (vcat [ lint_banner "errors" (ppr pass), Err.pprMessageBag errs
                  , text "*** Offending Program ***"
                  , pprCoreBindings binds
@@ -294,7 +294,7 @@ displayLintResults dflags pass warns errs binds
   | not (isEmptyBag warns)
   , not opt_NoDebugOutput
   , showLintWarnings pass
-  = log_action dflags dflags Err.SevDump noSrcSpan defaultDumpStyle
+  = log_action dflags dflags Nothing Err.SevDump noSrcSpan defaultDumpStyle
         (lint_banner "warnings" (ppr pass) $$ Err.pprMessageBag warns)
 
   | otherwise = return ()
@@ -324,7 +324,8 @@ lintInteractiveExpr what hsc_env expr
     dflags = hsc_dflags hsc_env
 
     display_lint_err err
-      = do { log_action dflags dflags Err.SevDump noSrcSpan defaultDumpStyle
+      = do { log_action dflags dflags Nothing Err.SevDump
+               noSrcSpan defaultDumpStyle
                (vcat [ lint_banner "errors" (text what)
                      , err
                      , text "*** Offending Program ***"
diff --git a/compiler/deSugar/Coverage.hs b/compiler/deSugar/Coverage.hs
index ef21f5c4d4..7acf258236 100644
--- a/compiler/deSugar/Coverage.hs
+++ b/compiler/deSugar/Coverage.hs
@@ -111,7 +111,7 @@ addTicksToBinds hsc_env mod mod_loc exports tyCons binds
      modBreaks <- mkModBreaks hsc_env mod tickCount entries
 
      when (dopt Opt_D_dump_ticked dflags) $
-         log_action dflags dflags SevDump noSrcSpan defaultDumpStyle
+         log_action dflags dflags Nothing SevDump noSrcSpan defaultDumpStyle
              (pprLHsBinds binds1)
 
      return (binds1, HpcInfo tickCount hashNo, Just modBreaks)
diff --git a/compiler/ghci/Debugger.hs b/compiler/ghci/Debugger.hs
index 81aab36ea9..64244729c4 100644
--- a/compiler/ghci/Debugger.hs
+++ b/compiler/ghci/Debugger.hs
@@ -170,7 +170,7 @@ showTerm term = do
                       -- XXX: this tries to disable logging of errors
                       -- does this still do what it is intended to do
                       -- with the changed error handling and logging?
-           let noop_log _ _ _ _ _ = return ()
+           let noop_log _ _ _ _ _ _ = return ()
                expr = "show " ++ showPpr dflags bname
            _ <- GHC.setSessionDynFlags dflags{log_action=noop_log}
            fhv <- liftIO $ mkFinalizedHValue hsc_env =<< mkRemoteRef val
diff --git a/compiler/ghci/Linker.hs b/compiler/ghci/Linker.hs
index 2b471ee0ee..a434d242b7 100644
--- a/compiler/ghci/Linker.hs
+++ b/compiler/ghci/Linker.hs
@@ -235,7 +235,7 @@ withExtendedLinkEnv new_env action
 showLinkerState :: DynFlags -> IO ()
 showLinkerState dflags
   = do pls <- readIORef v_PersistentLinkerState >>= readMVar
-       log_action dflags dflags SevDump noSrcSpan defaultDumpStyle
+       log_action dflags dflags Nothing SevDump noSrcSpan defaultDumpStyle
                  (vcat [text "----- Linker state -----",
                         text "Pkgs:" <+> ppr (pkgs_loaded pls),
                         text "Objs:" <+> ppr (objs_loaded pls),
@@ -374,7 +374,7 @@ classifyLdInput dflags f
   | isObjectFilename platform f = return (Just (Object f))
   | isDynLibFilename platform f = return (Just (DLLPath f))
   | otherwise          = do
-        log_action dflags dflags SevInfo noSrcSpan defaultUserStyle
+        log_action dflags dflags Nothing SevInfo noSrcSpan defaultUserStyle
             (text ("Warning: ignoring unrecognised input `" ++ f ++ "'"))
         return Nothing
     where platform = targetPlatform dflags
@@ -1397,7 +1397,8 @@ maybePutStr :: DynFlags -> String -> IO ()
 maybePutStr dflags s
     = when (verbosity dflags > 1) $
           do let act = log_action dflags
-             act dflags SevInteractive noSrcSpan defaultUserStyle (text s)
+             act dflags Nothing SevInteractive noSrcSpan defaultUserStyle
+                 (text s)
 
 maybePutStrLn :: DynFlags -> String -> IO ()
 maybePutStrLn dflags s = maybePutStr dflags (s ++ "\n")
diff --git a/compiler/iface/BinIface.hs b/compiler/iface/BinIface.hs
index c0926fc22e..470fe3a255 100644
--- a/compiler/iface/BinIface.hs
+++ b/compiler/iface/BinIface.hs
@@ -80,7 +80,9 @@ readBinIface_ :: DynFlags -> CheckHiWay -> TraceBinIFaceReading -> FilePath
 readBinIface_ dflags checkHiWay traceBinIFaceReading hi_path ncu = do
     let printer :: SDoc -> IO ()
         printer = case traceBinIFaceReading of
-                      TraceBinIFaceReading -> \sd -> log_action dflags dflags SevOutput noSrcSpan defaultDumpStyle sd
+                      TraceBinIFaceReading -> \sd ->
+                          log_action dflags dflags Nothing SevOutput
+                                     noSrcSpan defaultDumpStyle sd
                       QuietBinIFaceReading -> \_ -> return ()
         wantedGot :: Outputable a => String -> a -> a -> IO ()
         wantedGot what wanted got =
diff --git a/compiler/iface/LoadIface.hs b/compiler/iface/LoadIface.hs
index c044136b36..daf9f2ecbb 100644
--- a/compiler/iface/LoadIface.hs
+++ b/compiler/iface/LoadIface.hs
@@ -861,7 +861,8 @@ showIface hsc_env filename = do
    iface <- initTcRnIf 's' hsc_env () () $
        readBinIface IgnoreHiWay TraceBinIFaceReading filename
    let dflags = hsc_dflags hsc_env
-   log_action dflags dflags SevDump noSrcSpan defaultDumpStyle (pprModIface iface)
+   log_action dflags dflags Nothing SevDump noSrcSpan defaultDumpStyle
+              (pprModIface iface)
 
 pprModIface :: ModIface -> SDoc
 -- Show a ModIface
diff --git a/compiler/main/CodeOutput.hs b/compiler/main/CodeOutput.hs
index 00a0801c47..083133c70f 100644
--- a/compiler/main/CodeOutput.hs
+++ b/compiler/main/CodeOutput.hs
@@ -67,7 +67,7 @@ codeOutput dflags this_mod filenm location foreign_stubs pkg_deps cmm_stream
               do_lint cmm = do
                 { showPass dflags "CmmLint"
                 ; case cmmLint dflags cmm of
-                        Just err -> do { log_action dflags dflags SevDump noSrcSpan defaultDumpStyle err
+                        Just err -> do { log_action dflags dflags Nothing SevDump noSrcSpan defaultDumpStyle err
                                        ; ghcExit dflags 1
                                        }
                         Nothing  -> return ()
diff --git a/compiler/main/DriverPipeline.hs b/compiler/main/DriverPipeline.hs
index 3de94fd403..bbc190812e 100644
--- a/compiler/main/DriverPipeline.hs
+++ b/compiler/main/DriverPipeline.hs
@@ -1594,7 +1594,7 @@ mkExtraObj dflags extn xs
 mkExtraObjToLinkIntoBinary :: DynFlags -> IO FilePath
 mkExtraObjToLinkIntoBinary dflags = do
    when (gopt Opt_NoHsMain dflags && haveRtsOptsFlags dflags) $ do
-      log_action dflags dflags SevInfo noSrcSpan defaultUserStyle
+      log_action dflags dflags Nothing SevInfo noSrcSpan defaultUserStyle
           (text "Warning: -rtsopts and -with-rtsopts have no effect with -no-hs-main." $$
            text "    Call hs_init_ghc() from your main() function to set these options.")
 
@@ -1969,7 +1969,7 @@ linkDynLibCheck :: DynFlags -> [String] -> [UnitId] -> IO ()
 linkDynLibCheck dflags o_files dep_packages
  = do
     when (haveRtsOptsFlags dflags) $ do
-      log_action dflags dflags SevInfo noSrcSpan defaultUserStyle
+      log_action dflags dflags Nothing SevInfo noSrcSpan defaultUserStyle
           (text "Warning: -rtsopts and -with-rtsopts have no effect with -shared." $$
            text "    Call hs_init_ghc() from your main() function to set these options.")
 
diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index 52da3005bf..df95312edc 100644
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -173,7 +173,7 @@ import FastString
 import Outputable
 import Foreign.C        ( CInt(..) )
 import System.IO.Unsafe ( unsafeDupablePerformIO )
-import {-# SOURCE #-} ErrUtils ( Severity(..), MsgDoc, mkLocMessage )
+import {-# SOURCE #-} ErrUtils ( Severity(..), MsgDoc, mkLocMessageAnn )
 
 import System.IO.Unsafe ( unsafePerformIO )
 import Data.IORef
@@ -1616,13 +1616,13 @@ interpreterDynamic dflags
 --------------------------------------------------------------------------
 
 type FatalMessager = String -> IO ()
-type LogAction = DynFlags -> Severity -> SrcSpan -> PprStyle -> MsgDoc -> IO ()
+type LogAction = DynFlags -> Maybe WarningFlag -> Severity -> SrcSpan -> PprStyle -> MsgDoc -> IO ()
 
 defaultFatalMessager :: FatalMessager
 defaultFatalMessager = hPutStrLn stderr
 
 defaultLogAction :: LogAction
-defaultLogAction dflags severity srcSpan style msg
+defaultLogAction dflags flag severity srcSpan style msg
     = case severity of
       SevOutput      -> printSDoc msg style
       SevDump        -> printSDoc (msg $$ blankLine) style
@@ -1630,7 +1630,7 @@ defaultLogAction dflags severity srcSpan style msg
       SevInfo        -> printErrs msg style
       SevFatal       -> printErrs msg style
       _              -> do hPutChar stderr '\n'
-                           printErrs (mkLocMessage severity srcSpan msg) style
+                           printErrs (mkLocMessageAnn flagMsg severity srcSpan msg) style
                            -- careful (#2302): printErrs prints in UTF-8,
                            -- whereas converting to string first and using
                            -- hPutStr would just emit the low 8 bits of
@@ -1638,6 +1638,9 @@ defaultLogAction dflags severity srcSpan style msg
     where printSDoc  = defaultLogActionHPrintDoc  dflags stdout
           printErrs  = defaultLogActionHPrintDoc  dflags stderr
           putStrSDoc = defaultLogActionHPutStrDoc dflags stdout
+          -- Pretty print the warning flag, if any (#10752)
+          flagMsg = (\wf -> '-':'W':flagSpecName wf) <$> (flag >>= \f ->
+            listToMaybe $ filter (\fs -> flagSpecFlag fs == f) wWarningFlags)
 
 defaultLogActionHPrintDoc :: DynFlags -> Handle -> SDoc -> PprStyle -> IO ()
 defaultLogActionHPrintDoc dflags h d sty
diff --git a/compiler/main/ErrUtils.hs b/compiler/main/ErrUtils.hs
index eafe4e802f..585cab5f22 100644
--- a/compiler/main/ErrUtils.hs
+++ b/compiler/main/ErrUtils.hs
@@ -23,7 +23,7 @@ module ErrUtils (
         pprLocErrMsg, printBagOfErrors,
 
         -- ** Construction
-        emptyMessages, mkLocMessage, makeIntoWarning,
+        emptyMessages, mkLocMessage, mkLocMessageAnn, makeIntoWarning,
         mkErrMsg, mkPlainErrMsg, mkErrDoc, mkLongErrMsg, mkWarnMsg,
         mkPlainWarnMsg,
         warnIsErrorMsg, mkLongWarnMsg,
@@ -110,7 +110,8 @@ data ErrMsg = ErrMsg {
         errMsgDoc         :: ErrDoc,
         -- | This has the same text as errDocImportant . errMsgDoc.
         errMsgShortString :: String,
-        errMsgSeverity    :: Severity
+        errMsgSeverity    :: Severity,
+        errMsgFlag        :: Maybe WarningFlag
         }
         -- The SrcSpan is used for sorting errors into line-number order
 
@@ -160,15 +161,18 @@ pprMessageBag :: Bag MsgDoc -> SDoc
 pprMessageBag msgs = vcat (punctuate blankLine (bagToList msgs))
 
 mkLocMessage :: Severity -> SrcSpan -> MsgDoc -> MsgDoc
+mkLocMessage = mkLocMessageAnn Nothing
+
+mkLocMessageAnn :: Maybe String -> Severity -> SrcSpan -> MsgDoc -> MsgDoc
   -- Always print the location, even if it is unhelpful.  Error messages
   -- are supposed to be in a standard format, and one without a location
   -- would look strange.  Better to say explicitly "<no location info>".
-mkLocMessage severity locn msg
+mkLocMessageAnn ann severity locn msg
     = sdocWithDynFlags $ \dflags ->
       let locn' = if gopt Opt_ErrorSpans dflags
                   then ppr locn
                   else ppr (srcSpanStart locn)
-      in hang (locn' <> colon <+> sev_info) 4 msg
+      in hang (locn' <> colon <+> sev_info <> opt_ann) 4 msg
   where
     -- Add prefixes, like    Foo.hs:34: warning:
     --                           <the warning message>
@@ -178,8 +182,13 @@ mkLocMessage severity locn msg
                  SevFatal -> text "fatal:"
                  _ -> empty
 
-makeIntoWarning :: ErrMsg -> ErrMsg
-makeIntoWarning err = err { errMsgSeverity = SevWarning }
+    -- Add optional information
+    opt_ann = text $ maybe "" (\i -> " ["++i++"]") ann
+
+makeIntoWarning :: Maybe WarningFlag -> ErrMsg -> ErrMsg
+makeIntoWarning flag err
+= err { errMsgSeverity = SevWarning
+      , errMsgFlag = flag }
 
 -- -----------------------------------------------------------------------------
 -- Collecting up messages for later ordering and printing.
@@ -190,7 +199,8 @@ mk_err_msg dflags sev locn print_unqual doc
           , errMsgContext = print_unqual
           , errMsgDoc = doc
           , errMsgShortString = showSDoc dflags (vcat (errDocImportant doc))
-          , errMsgSeverity = sev }
+          , errMsgSeverity = sev
+          , errMsgFlag = Nothing }
 
 mkErrDoc :: DynFlags -> SrcSpan -> PrintUnqualified -> ErrDoc -> ErrMsg
 mkErrDoc dflags = mk_err_msg dflags SevError
@@ -226,10 +236,11 @@ errorsFound _dflags (_warns, errs) = not (isEmptyBag errs)
 printBagOfErrors :: DynFlags -> Bag ErrMsg -> IO ()
 printBagOfErrors dflags bag_of_errors
   = sequence_ [ let style = mkErrStyle dflags unqual
-                in log_action dflags dflags sev s style (formatErrDoc dflags doc)
+                in log_action dflags dflags flag sev s style (formatErrDoc dflags doc)
               | ErrMsg { errMsgSpan      = s,
                          errMsgDoc       = doc,
                          errMsgSeverity  = sev,
+                         errMsgFlag      = flag,
                          errMsgContext   = unqual } <- sortMsgBag (Just dflags)
                                                                   bag_of_errors ]
 
@@ -283,7 +294,8 @@ doIfSet_dyn dflags flag action | gopt flag dflags = action
 dumpIfSet :: DynFlags -> Bool -> String -> SDoc -> IO ()
 dumpIfSet dflags flag hdr doc
   | not flag   = return ()
-  | otherwise  = log_action dflags dflags SevDump noSrcSpan defaultDumpStyle (mkDumpDoc hdr doc)
+  | otherwise  = log_action dflags dflags Nothing SevDump
+                            noSrcSpan defaultDumpStyle (mkDumpDoc hdr doc)
 
 -- | a wrapper around 'dumpSDoc'.
 -- First check whether the dump flag is set
@@ -359,7 +371,7 @@ dumpSDoc dflags print_unqual flag hdr doc
               let (doc', severity)
                     | null hdr  = (doc, SevOutput)
                     | otherwise = (mkDumpDoc hdr doc, SevDump)
-              log_action dflags dflags severity noSrcSpan dump_style doc'
+              log_action dflags dflags Nothing severity noSrcSpan dump_style doc'
 
 
 -- | Choose where to put a dump file based on DynFlags
@@ -416,18 +428,20 @@ ifVerbose dflags val act
 
 errorMsg :: DynFlags -> MsgDoc -> IO ()
 errorMsg dflags msg
-   = log_action dflags dflags SevError noSrcSpan (defaultErrStyle dflags) msg
+   = log_action dflags dflags Nothing SevError noSrcSpan
+                (defaultErrStyle dflags) msg
 
 warningMsg :: DynFlags -> MsgDoc -> IO ()
 warningMsg dflags msg
-   = log_action dflags dflags SevWarning noSrcSpan (defaultErrStyle dflags) msg
+   = log_action dflags dflags Nothing SevWarning noSrcSpan
+                (defaultErrStyle dflags) msg
 
 fatalErrorMsg :: DynFlags -> MsgDoc -> IO ()
 fatalErrorMsg dflags msg = fatalErrorMsg' (log_action dflags) dflags msg
 
 fatalErrorMsg' :: LogAction -> DynFlags -> MsgDoc -> IO ()
 fatalErrorMsg' la dflags msg =
-    la dflags SevFatal noSrcSpan (defaultErrStyle dflags) msg
+    la dflags Nothing SevFatal noSrcSpan (defaultErrStyle dflags) msg
 
 fatalErrorMsg'' :: FatalMessager -> String -> IO ()
 fatalErrorMsg'' fm msg = fm msg
@@ -458,11 +472,13 @@ printOutputForUser dflags print_unqual msg
   = logOutput dflags (mkUserStyle print_unqual AllTheWay) msg
 
 logInfo :: DynFlags -> PprStyle -> MsgDoc -> IO ()
-logInfo dflags sty msg = log_action dflags dflags SevInfo noSrcSpan sty msg
+logInfo dflags sty msg
+  = log_action dflags dflags Nothing SevInfo noSrcSpan sty msg
 
 logOutput :: DynFlags -> PprStyle -> MsgDoc -> IO ()
 -- ^ Like 'logInfo' but with 'SevOutput' rather then 'SevInfo'
-logOutput dflags sty msg = log_action dflags dflags SevOutput noSrcSpan sty msg
+logOutput dflags sty msg
+  = log_action dflags dflags Nothing SevOutput noSrcSpan sty msg
 
 prettyPrintGhcErrors :: ExceptionMonad m => DynFlags -> m a -> m a
 prettyPrintGhcErrors dflags
diff --git a/compiler/main/ErrUtils.hs-boot b/compiler/main/ErrUtils.hs-boot
index 31edcc05ee..b991ec4958 100644
--- a/compiler/main/ErrUtils.hs-boot
+++ b/compiler/main/ErrUtils.hs-boot
@@ -16,3 +16,4 @@ data Severity
 type MsgDoc = SDoc
 
 mkLocMessage :: Severity -> SrcSpan -> MsgDoc -> MsgDoc
+mkLocMessageAnn :: Maybe String -> Severity -> SrcSpan -> MsgDoc -> MsgDoc
diff --git a/compiler/main/GhcMake.hs b/compiler/main/GhcMake.hs
index 7bbe4be495..3e62d8dea4 100644
--- a/compiler/main/GhcMake.hs
+++ b/compiler/main/GhcMake.hs
@@ -678,7 +678,7 @@ checkStability hpt sccs all_home_mods = foldl checkSCC ([],[]) sccs
 -- | Each module is given a unique 'LogQueue' to redirect compilation messages
 -- to. A 'Nothing' value contains the result of compilation, and denotes the
 -- end of the message queue.
-data LogQueue = LogQueue !(IORef [Maybe (Severity, SrcSpan, PprStyle, MsgDoc)])
+data LogQueue = LogQueue !(IORef [Maybe (Maybe WarningFlag, Severity, SrcSpan, PprStyle, MsgDoc)])
                          !(MVar ())
 
 -- | The graph of modules to compile and their corresponding result 'MVar' and
@@ -879,7 +879,7 @@ parUpsweep n_jobs old_hpt stable_mods cleanup sccs = do
             return (success_flag,ok_results)
 
   where
-    writeLogQueue :: LogQueue -> Maybe (Severity,SrcSpan,PprStyle,MsgDoc) -> IO ()
+    writeLogQueue :: LogQueue -> Maybe (Maybe WarningFlag,Severity,SrcSpan,PprStyle,MsgDoc) -> IO ()
     writeLogQueue (LogQueue ref sem) msg = do
         atomicModifyIORef' ref $ \msgs -> (msg:msgs,())
         _ <- tryPutMVar sem ()
@@ -888,8 +888,8 @@ parUpsweep n_jobs old_hpt stable_mods cleanup sccs = do
     -- The log_action callback that is used to synchronize messages from a
     -- worker thread.
     parLogAction :: LogQueue -> LogAction
-    parLogAction log_queue _dflags !severity !srcSpan !style !msg = do
-        writeLogQueue log_queue (Just (severity,srcSpan,style,msg))
+    parLogAction log_queue _dflags !flag !severity !srcSpan !style !msg = do
+        writeLogQueue log_queue (Just (flag,severity,srcSpan,style,msg))
 
     -- Print each message from the log_queue using the log_action from the
     -- session's DynFlags.
@@ -902,8 +902,8 @@ parUpsweep n_jobs old_hpt stable_mods cleanup sccs = do
 
             print_loop [] = read_msgs
             print_loop (x:xs) = case x of
-                Just (severity,srcSpan,style,msg) -> do
-                    log_action dflags dflags severity srcSpan style msg
+                Just (flag,severity,srcSpan,style,msg) -> do
+                    log_action dflags dflags flag severity srcSpan style msg
                     print_loop xs
                 -- Exit the loop once we encounter the end marker.
                 Nothing -> return ()
diff --git a/compiler/main/SysTools.hs b/compiler/main/SysTools.hs
index c3436edd9e..d7de69ae8d 100644
--- a/compiler/main/SysTools.hs
+++ b/compiler/main/SysTools.hs
@@ -1367,10 +1367,12 @@ builderMainLoop dflags filter_fn pgm real_args mb_env = do
               msg <- readChan chan
               case msg of
                 BuildMsg msg -> do
-                  log_action dflags dflags SevInfo noSrcSpan defaultUserStyle msg
+                  log_action dflags dflags Nothing SevInfo noSrcSpan
+                             defaultUserStyle msg
                   loop chan hProcess t p exitcode
                 BuildError loc msg -> do
-                  log_action dflags dflags SevError (mkSrcSpan loc loc) defaultUserStyle msg
+                  log_action dflags dflags Nothing SevError (mkSrcSpan loc loc)
+                             defaultUserStyle msg
                   loop chan hProcess t p exitcode
                 EOF ->
                   loop chan hProcess (t-1) p exitcode
diff --git a/compiler/main/TidyPgm.hs b/compiler/main/TidyPgm.hs
index df31fda16c..072fb840a4 100644
--- a/compiler/main/TidyPgm.hs
+++ b/compiler/main/TidyPgm.hs
@@ -390,7 +390,8 @@ tidyProgram hsc_env  (ModGuts { mg_module    = mod
           -- Print one-line size info
         ; let cs = coreBindsStats tidy_binds
         ; when (dopt Opt_D_dump_core_stats dflags)
-               (log_action dflags dflags SevDump noSrcSpan defaultDumpStyle
+               (log_action dflags dflags Nothing SevDump noSrcSpan
+                          defaultDumpStyle
                           (text "Tidy size (terms,types,coercions)"
                            <+> ppr (moduleName mod) <> colon
                            <+> int (cs_tm cs)
diff --git a/compiler/rename/RnBinds.hs b/compiler/rename/RnBinds.hs
index 33a1cb447b..be103e5b24 100644
--- a/compiler/rename/RnBinds.hs
+++ b/compiler/rename/RnBinds.hs
@@ -462,7 +462,7 @@ rnBind _ bind@(PatBind { pat_lhs = pat
         --           or an occurrence of, a variable on the RHS
         ; whenWOptM Opt_WarnUnusedPatternBinds $
           when (null bndrs && not is_wild_pat) $
-          addWarn $ unusedPatBindWarn bind'
+          addWarn Opt_WarnUnusedPatternBinds $ unusedPatBindWarn bind'
 
         ; fvs' `seq` -- See Note [Free-variable space leak]
           return (bind', bndrs, all_fvs) }
@@ -1104,7 +1104,7 @@ rnGRHS' ctxt rnBody (GRHS guards rhs)
                                     rnBody rhs
 
         ; unless (pattern_guards_allowed || is_standard_guard guards')
-                 (addWarn (nonStdGuardErr guards'))
+                 (addWarn' (nonStdGuardErr guards'))
 
         ; return (GRHS guards' rhs', fvs) }
   where
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)]
diff --git a/compiler/rename/RnNames.hs b/compiler/rename/RnNames.hs
index d8e08e20aa..33074dbde0 100644
--- a/compiler/rename/RnNames.hs
+++ b/compiler/rename/RnNames.hs
@@ -236,7 +236,8 @@ rnImportDecl this_mod
         _  | implicit   -> return () -- Do not bleat for implicit imports
            | qual_only  -> return ()
            | otherwise  -> whenWOptM Opt_WarnMissingImportList $
-                           addWarn (missingImportListWarn imp_mod_name)
+                           addWarn Opt_WarnMissingImportList
+                                   (missingImportListWarn imp_mod_name)
 
     iface <- loadSrcInterface doc imp_mod_name want_boot (fmap sl_fs mb_pkg)
 
@@ -253,8 +254,8 @@ rnImportDecl this_mod
     -- the non-boot module depends on the compilation order, which
     -- is not deterministic.  The hs-boot test can show this up.
     dflags <- getDynFlags
-    warnIf (want_boot && not (mi_boot iface) && isOneShot (ghcMode dflags))
-           (warnRedundantSourceImport imp_mod_name)
+    warnIf' (want_boot && not (mi_boot iface) && isOneShot (ghcMode dflags))
+            (warnRedundantSourceImport imp_mod_name)
     when (mod_safe && not (safeImportsOn dflags)) $
         addErr (text "safe import can't be used as Safe Haskell isn't on!"
                 $+$ ptext (sLit $ "please enable Safe Haskell through either "
@@ -297,7 +298,8 @@ rnImportDecl this_mod
     -- Complain if we import a deprecated module
     whenWOptM Opt_WarnWarningsDeprecations (
        case (mi_warns iface) of
-          WarnAll txt -> addWarn $ moduleWarn imp_mod_name txt
+          WarnAll txt -> addWarn Opt_WarnWarningsDeprecations
+                                (moduleWarn imp_mod_name txt)
           _           -> return ()
      )
 
@@ -814,11 +816,11 @@ filterImports iface decl_spec (Just (want_hiding, L l import_items))
         where
             -- Warn when importing T(..) if T was exported abstractly
             emit_warning (DodgyImport n) = whenWOptM Opt_WarnDodgyImports $
-              addWarn (dodgyImportWarn n)
+              addWarn Opt_WarnDodgyImports (dodgyImportWarn n)
             emit_warning MissingImportList = whenWOptM Opt_WarnMissingImportList $
-              addWarn (missingImportListItem ieRdr)
+              addWarn Opt_WarnMissingImportList (missingImportListItem ieRdr)
             emit_warning BadImportW = whenWOptM Opt_WarnDodgyImports $
-              addWarn (lookup_err_msg BadImport)
+              addWarn Opt_WarnDodgyImports (lookup_err_msg BadImport)
 
             run_lookup :: IELookupM a -> TcRn (Maybe a)
             run_lookup m = case m of
@@ -1262,7 +1264,8 @@ exports_from_avail (Just (L _ rdr_items)) rdr_env imports this_mod
                              | (L _ (IEModuleContents (L _ mod))) <- ie_names ]
         , mod `elem` earlier_mods    -- Duplicate export of M
         = do { warn_dup_exports <- woptM Opt_WarnDuplicateExports ;
-               warnIf warn_dup_exports (dupModuleExport mod) ;
+               warnIf Opt_WarnDuplicateExports warn_dup_exports
+                      (dupModuleExport mod) ;
                return acc }
 
         | otherwise
@@ -1276,7 +1279,8 @@ exports_from_avail (Just (L _ rdr_items)) rdr_env imports this_mod
                }
 
              ; checkErr exportValid (moduleNotImported mod)
-             ; warnIf (warnDodgyExports && exportValid && null gre_prs)
+             ; warnIf Opt_WarnDodgyExports
+                      (warnDodgyExports && exportValid && null gre_prs)
                       (nullModuleExport mod)
 
              ; traceRn (text "efa" <+> (ppr mod $$ ppr all_gres))
@@ -1373,7 +1377,8 @@ exports_from_avail (Just (L _ rdr_items)) rdr_env imports this_mod
              warnDodgyExports <- woptM Opt_WarnDodgyExports
              when (null gres) $
                   if isTyConName name
-                  then when warnDodgyExports $ addWarn (dodgyExportWarn name)
+                  then when warnDodgyExports $
+                           addWarn Opt_WarnDodgyExports (dodgyExportWarn name)
                   else -- This occurs when you export T(..), but
                        -- only import T abstractly, or T is a synonym.
                        addErr (exportItemErr ie)
@@ -1416,7 +1421,8 @@ check_occs ie occs names  -- 'names' are the entities specifed by 'ie'
             -- by two different module exports. See ticket #4478.
             -> do unless (dupExport_ok name ie ie') $ do
                       warn_dup_exports <- woptM Opt_WarnDuplicateExports
-                      warnIf warn_dup_exports (dupExportWarn name_occ ie ie')
+                      warnIf Opt_WarnDuplicateExports warn_dup_exports
+                             (dupExportWarn name_occ ie ie')
                   return occs
 
             | otherwise    -- Same occ name but different names: an error
@@ -1550,7 +1556,7 @@ warnUnusedImportDecls gbl_env
        ; traceRn (vcat [ text "Uses:" <+> ppr uses
                        , text "Import usage" <+> ppr usage])
        ; whenWOptM Opt_WarnUnusedImports $
-         mapM_ (warnUnusedImport fld_env) usage
+         mapM_ (warnUnusedImport Opt_WarnUnusedImports fld_env) usage
 
        ; whenGOptM Opt_D_dump_minimal_imports $
          printMinimalImports usage }
@@ -1570,9 +1576,14 @@ warnMissingSigs gbl_env
        ; warn_pat_syns      <- woptM Opt_WarnMissingPatSynSigs
 
        ; let sig_warn
-               | warn_only_exported = topSigWarnIfExported exports sig_ns
-               | warn_missing_sigs || warn_pat_syns = topSigWarn sig_ns
-               | otherwise          = noSigWarn
+               | warn_only_exported
+                   = topSigWarnIfExported Opt_WarnMissingExportedSigs exports sig_ns
+               | warn_missing_sigs
+                   = topSigWarn Opt_WarnMissingSigs sig_ns
+               | warn_pat_syns
+                   = topSigWarn Opt_WarnMissingPatSynSigs sig_ns
+               | otherwise
+                   = noSigWarn
 
 
        ; let binders = (if warn_pat_syns then ps_binders else [])
@@ -1591,35 +1602,36 @@ type SigWarn = [(Type, Name)] -> RnM ()
 noSigWarn :: SigWarn
 noSigWarn _ = return ()
 
-topSigWarnIfExported :: NameSet -> NameSet -> SigWarn
-topSigWarnIfExported exported sig_ns ids
-  = mapM_ (topSigWarnIdIfExported exported sig_ns) ids
+topSigWarnIfExported :: WarningFlag -> NameSet -> NameSet -> SigWarn
+topSigWarnIfExported flag exported sig_ns ids
+  = mapM_ (topSigWarnIdIfExported flag exported sig_ns) ids
 
-topSigWarnIdIfExported :: NameSet -> NameSet -> (Type, Name) -> RnM ()
-topSigWarnIdIfExported exported sig_ns (ty, name)
+topSigWarnIdIfExported :: WarningFlag -> NameSet -> NameSet -> (Type, Name)
+                       -> RnM ()
+topSigWarnIdIfExported flag exported sig_ns (ty, name)
   | name `elemNameSet` exported
-  = topSigWarnId sig_ns (ty, name)
+  = topSigWarnId flag sig_ns (ty, name)
   | otherwise
   = return ()
 
-topSigWarn :: NameSet -> SigWarn
-topSigWarn sig_ns ids = mapM_ (topSigWarnId sig_ns) ids
+topSigWarn :: WarningFlag -> NameSet -> SigWarn
+topSigWarn flag sig_ns ids = mapM_ (topSigWarnId flag sig_ns) ids
 
-topSigWarnId :: NameSet -> (Type, Name) -> RnM ()
+topSigWarnId :: WarningFlag -> NameSet -> (Type, Name) -> RnM ()
 -- The NameSet is the Ids that *lack* a signature
 -- We have to do it this way round because there are
 -- lots of top-level bindings that are generated by GHC
 -- and that don't have signatures
-topSigWarnId sig_ns (ty, name)
-  | name `elemNameSet` sig_ns      = warnMissingSig msg (ty, name)
+topSigWarnId flag sig_ns (ty, name)
+  | name `elemNameSet` sig_ns      = warnMissingSig flag msg (ty, name)
   | otherwise                      = return ()
   where
     msg = text "Top-level binding with no type signature:"
 
-warnMissingSig :: SDoc -> (Type, Name) -> RnM ()
-warnMissingSig msg (ty, name) = do
+warnMissingSig :: WarningFlag -> SDoc -> (Type, Name) -> RnM ()
+warnMissingSig flag msg (ty, name) = do
     tymsg <- getMsg ty
-    addWarnAt (getSrcSpan name) (mk_msg tymsg)
+    addWarnAt flag (getSrcSpan name) (mk_msg tymsg)
   where
     mk_msg endmsg = sep [ msg, nest 2 $ pprPrefixName name <+> endmsg ]
 
@@ -1723,9 +1735,9 @@ extendImportMap gre imp_map
                    -- For srcSpanEnd see Note [The ImportMap]
         avail    = availFromGRE gre
 
-warnUnusedImport :: NameEnv (FieldLabelString, Name) -> ImportDeclUsage
-                 -> RnM ()
-warnUnusedImport fld_env (L loc decl, used, unused)
+warnUnusedImport :: WarningFlag -> NameEnv (FieldLabelString, Name)
+                 -> ImportDeclUsage -> RnM ()
+warnUnusedImport flag fld_env (L loc decl, used, unused)
   | Just (False,L _ []) <- ideclHiding decl
                 = return ()            -- Do not warn for 'import M()'
 
@@ -1733,9 +1745,9 @@ warnUnusedImport fld_env (L loc decl, used, unused)
   , not (null hides)
   , pRELUDE_NAME == unLoc (ideclName decl)
                 = return ()            -- Note [Do not warn about Prelude hiding]
-  | null used   = addWarnAt loc msg1   -- Nothing used; drop entire decl
+  | null used   = addWarnAt flag loc msg1   -- Nothing used; drop entire decl
   | null unused = return ()            -- Everything imported is used; nop
-  | otherwise   = addWarnAt loc msg2   -- Some imports are unused
+  | otherwise   = addWarnAt flag loc msg2   -- Some imports are unused
   where
     msg1 = vcat [pp_herald <+> quotes pp_mod <+> pp_not_used,
                  nest 2 (text "except perhaps to import instances from"
diff --git a/compiler/rename/RnSource.hs b/compiler/rename/RnSource.hs
index 4f655090c6..5c5e1b1d3e 100644
--- a/compiler/rename/RnSource.hs
+++ b/compiler/rename/RnSource.hs
@@ -500,10 +500,12 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == pureAName, isAliasMG mg == Just returnMName
-                      -> addWarnNonCanonicalMethod1 "pure" "return"
+                      -> addWarnNonCanonicalMethod1
+                            Opt_WarnNonCanonicalMonadInstances "pure" "return"
 
                       | name == thenAName, isAliasMG mg == Just thenMName
-                      -> addWarnNonCanonicalMethod1 "(*>)" "(>>)"
+                      -> addWarnNonCanonicalMethod1
+                            Opt_WarnNonCanonicalMonadInstances "(*>)" "(>>)"
 
                   _ -> return ()
 
@@ -512,10 +514,12 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == returnMName, isAliasMG mg /= Just pureAName
-                      -> addWarnNonCanonicalMethod2 "return" "pure"
+                      -> addWarnNonCanonicalMethod2
+                            Opt_WarnNonCanonicalMonadInstances "return" "pure"
 
                       | name == thenMName, isAliasMG mg /= Just thenAName
-                      -> addWarnNonCanonicalMethod2 "(>>)" "(*>)"
+                      -> addWarnNonCanonicalMethod2
+                            Opt_WarnNonCanonicalMonadInstances "(>>)" "(*>)"
 
                   _ -> return ()
 
@@ -540,7 +544,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == failMName, isAliasMG mg == Just failMName_preMFP
-                      -> addWarnNonCanonicalMethod1 "fail" "Control.Monad.fail"
+                      -> addWarnNonCanonicalMethod1
+                            Opt_WarnNonCanonicalMonadFailInstances "fail"
+                            "Control.Monad.fail"
 
                   _ -> return ()
 
@@ -549,8 +555,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == failMName_preMFP, isAliasMG mg /= Just failMName
-                      -> addWarnNonCanonicalMethod2 "fail"
-                                                    "Control.Monad.Fail.fail"
+                      -> addWarnNonCanonicalMethod2
+                            Opt_WarnNonCanonicalMonadFailInstances "fail"
+                            "Control.Monad.Fail.fail"
                   _ -> return ()
 
       | otherwise = return ()
@@ -574,7 +581,8 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == sappendName, isAliasMG mg == Just mappendName
-                      -> addWarnNonCanonicalMethod1 "(<>)" "mappend"
+                      -> addWarnNonCanonicalMethod1
+                            Opt_WarnNonCanonicalMonoidInstances "(<>)" "mappend"
 
                   _ -> return ()
 
@@ -583,7 +591,8 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == mappendName, isAliasMG mg /= Just sappendName
-                      -> addWarnNonCanonicalMethod2NoDefault "mappend" "(<>)"
+                      -> addWarnNonCanonicalMethod2NoDefault
+                            Opt_WarnNonCanonicalMonoidInstances "mappend" "(<>)"
 
                   _ -> return ()
 
@@ -599,8 +608,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
     isAliasMG _ = Nothing
 
     -- got "lhs = rhs" but expected something different
-    addWarnNonCanonicalMethod1 lhs rhs = do
-        addWarn $ vcat [ text "Noncanonical" <+>
+    addWarnNonCanonicalMethod1 flag lhs rhs = do
+        addWarn flag $ vcat
+                       [ text "Noncanonical" <+>
                          quotes (text (lhs ++ " = " ++ rhs)) <+>
                          text "definition detected"
                        , instDeclCtxt1 poly_ty
@@ -610,8 +620,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
                        ]
 
     -- expected "lhs = rhs" but got something else
-    addWarnNonCanonicalMethod2 lhs rhs = do
-        addWarn $ vcat [ text "Noncanonical" <+>
+    addWarnNonCanonicalMethod2 flag lhs rhs = do
+        addWarn flag $ vcat
+                       [ text "Noncanonical" <+>
                          quotes (text lhs) <+>
                          text "definition detected"
                        , instDeclCtxt1 poly_ty
@@ -621,8 +632,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
                        ]
 
     -- like above, but method has no default impl
-    addWarnNonCanonicalMethod2NoDefault lhs rhs = do
-        addWarn $ vcat [ text "Noncanonical" <+>
+    addWarnNonCanonicalMethod2NoDefault flag lhs rhs = do
+        addWarn flag $ vcat
+                       [ text "Noncanonical" <+>
                          quotes (text lhs) <+>
                          text "definition detected"
                        , instDeclCtxt1 poly_ty
diff --git a/compiler/rename/RnTypes.hs b/compiler/rename/RnTypes.hs
index 118a32b392..b729e3befc 100644
--- a/compiler/rename/RnTypes.hs
+++ b/compiler/rename/RnTypes.hs
@@ -1409,7 +1409,7 @@ warnUnusedForAll :: SDoc -> LHsTyVarBndr Name -> FreeVars -> TcM ()
 warnUnusedForAll in_doc (L loc tv) used_names
   = whenWOptM Opt_WarnUnusedForalls $
     unless (hsTyVarName tv `elemNameSet` used_names) $
-    addWarnAt loc $
+    addWarnAt Opt_WarnUnusedForalls loc $
     vcat [ text "Unused quantified type variable" <+> quotes (ppr tv)
          , in_doc ]
 
diff --git a/compiler/simplCore/CoreMonad.hs b/compiler/simplCore/CoreMonad.hs
index 13a7512ffa..36c6d87db1 100644
--- a/compiler/simplCore/CoreMonad.hs
+++ b/compiler/simplCore/CoreMonad.hs
@@ -825,7 +825,7 @@ msg sev doc
              user_sty = mkUserStyle unqual AllTheWay
              dump_sty = mkDumpStyle unqual
        ; liftIO $
-         (log_action dflags) dflags sev loc sty doc }
+         (log_action dflags) dflags Nothing sev loc sty doc }
 
 -- | Output a String message to the screen
 putMsgS :: String -> CoreM ()
diff --git a/compiler/simplCore/SimplCore.hs b/compiler/simplCore/SimplCore.hs
index 6badbf83db..61c0491bf5 100644
--- a/compiler/simplCore/SimplCore.hs
+++ b/compiler/simplCore/SimplCore.hs
@@ -428,7 +428,8 @@ ruleCheckPass current_phase pat guts = do
     dflags <- getDynFlags
     vis_orphs <- getVisibleOrphanMods
     liftIO $ Err.showPass dflags "RuleCheck"
-    liftIO $ log_action dflags dflags Err.SevDump noSrcSpan defaultDumpStyle
+    liftIO $ log_action dflags dflags Nothing Err.SevDump noSrcSpan
+                 defaultDumpStyle
                  (ruleCheckProgram current_phase pat
                     (RuleEnv rb vis_orphs) (mg_binds guts))
     return guts
diff --git a/compiler/simplStg/SimplStg.hs b/compiler/simplStg/SimplStg.hs
index b8491fcbbe..8ea661d5f2 100644
--- a/compiler/simplStg/SimplStg.hs
+++ b/compiler/simplStg/SimplStg.hs
@@ -37,7 +37,8 @@ stg2stg dflags module_name binds
         ; us <- mkSplitUniqSupply 'g'
 
         ; when (dopt Opt_D_verbose_stg2stg dflags)
-               (log_action dflags dflags SevDump noSrcSpan defaultDumpStyle (text "VERBOSE STG-TO-STG:"))
+               (log_action dflags dflags Nothing SevDump noSrcSpan
+                           defaultDumpStyle (text "VERBOSE STG-TO-STG:"))
 
         ; (binds', us', ccs) <- end_pass us "Stg2Stg" ([],[],[]) binds
 
diff --git a/compiler/typecheck/Inst.hs b/compiler/typecheck/Inst.hs
index b3da5ef5ea..03dad405a0 100644
--- a/compiler/typecheck/Inst.hs
+++ b/compiler/typecheck/Inst.hs
@@ -520,7 +520,9 @@ newClsInst overlap_mode dfun_name tvs theta clas tys
        ; oflag <- getOverlapFlag overlap_mode
        ; let inst = mkLocalInstance dfun oflag tvs' clas tys'
        ; dflags <- getDynFlags
-       ; warnIf (isOrphan (is_orphan inst) && wopt Opt_WarnOrphans dflags) (instOrphWarn inst)
+       ; warnIf Opt_WarnOrphans
+             (isOrphan (is_orphan inst) && wopt Opt_WarnOrphans dflags)
+             (instOrphWarn inst)
        ; return inst }
 
 instOrphWarn :: ClsInst -> SDoc
diff --git a/compiler/typecheck/TcAnnotations.hs b/compiler/typecheck/TcAnnotations.hs
index b80d5bd236..e1bb975abf 100644
--- a/compiler/typecheck/TcAnnotations.hs
+++ b/compiler/typecheck/TcAnnotations.hs
@@ -29,7 +29,7 @@ tcAnnotations :: [LAnnDecl Name] -> TcM [Annotation]
 -- No GHCI; emit a warning (not an error) and ignore. cf Trac #4268
 tcAnnotations [] = return []
 tcAnnotations anns@(L loc _ : _)
-  = do { setSrcSpan loc $ addWarnTc $
+  = do { setSrcSpan loc $ addWarnTc' $
              (text "Ignoring ANN annotation" <> plural anns <> comma
              <+> text "because this is a stage-1 compiler or doesn't support GHCi")
        ; return [] }
diff --git a/compiler/typecheck/TcBinds.hs b/compiler/typecheck/TcBinds.hs
index 43f933b70d..3835bf185c 100644
--- a/compiler/typecheck/TcBinds.hs
+++ b/compiler/typecheck/TcBinds.hs
@@ -707,7 +707,8 @@ mkExport prag_fn qtvs theta
                        tcSubType_NC sig_ctxt sel_poly_ty (mkCheckExpType poly_ty)
 
         ; warn_missing_sigs <- woptM Opt_WarnMissingLocalSigs
-        ; when warn_missing_sigs $ localSigWarn poly_id mb_sig
+        ; when warn_missing_sigs $
+              localSigWarn Opt_WarnMissingLocalSigs poly_id mb_sig
 
         ; return (ABE { abe_wrap = wrap
                         -- abe_wrap :: idType poly_id ~ (forall qtvs. theta => mono_ty)
@@ -797,7 +798,8 @@ chooseInferredQuantifiers inferred_theta tau_tvs qtvs
                  , ppr annotated_theta, ppr inferred_theta
                  , ppr inferred_diff ]
        ; case partial_sigs of
-           True | warn_partial_sigs -> reportWarning msg
+           True | warn_partial_sigs ->
+                      reportWarning (Just Opt_WarnPartialTypeSignatures) msg
                 | otherwise         -> return ()
            False                    -> reportError msg
 
@@ -851,19 +853,19 @@ mk_inf_msg poly_name poly_ty tidy_env
 
 
 -- | Warn the user about polymorphic local binders that lack type signatures.
-localSigWarn :: Id -> Maybe TcIdSigInfo -> TcM ()
-localSigWarn id mb_sig
+localSigWarn :: WarningFlag -> Id -> Maybe TcIdSigInfo -> TcM ()
+localSigWarn flag id mb_sig
   | Just _ <- mb_sig               = return ()
   | not (isSigmaTy (idType id))    = return ()
-  | otherwise                      = warnMissingSig msg id
+  | otherwise                      = warnMissingSig flag msg id
   where
     msg = text "Polymorphic local binding with no type signature:"
 
-warnMissingSig :: SDoc -> Id -> TcM ()
-warnMissingSig msg id
+warnMissingSig :: WarningFlag -> SDoc -> Id -> TcM ()
+warnMissingSig flag msg id
   = do  { env0 <- tcInitTidyEnv
         ; let (env1, tidy_ty) = tidyOpenType env0 (idType id)
-        ; addWarnTcM (env1, mk_msg tidy_ty) }
+        ; addWarnTcM flag (env1, mk_msg tidy_ty) }
   where
     mk_msg ty = sep [ msg, nest 2 $ pprPrefixName (idName id) <+> dcolon <+> ppr ty ]
 
@@ -1126,7 +1128,7 @@ tcSpecPrags poly_id prag_sigs
     is_bad_sig s = not (isSpecLSig s || isInlineLSig s)
 
     warn_discarded_sigs
-      = addWarnTc (hang (text "Discarding unexpected pragmas for" <+> ppr poly_id)
+      = addWarnTc' (hang (text "Discarding unexpected pragmas for" <+> ppr poly_id)
                       2 (vcat (map (ppr . getLoc) bad_sigs)))
 
 --------------
@@ -1140,7 +1142,7 @@ tcSpecPrag poly_id prag@(SpecSig fun_name hs_tys inl)
 -- However we want to use fun_name in the error message, since that is
 -- what the user wrote (Trac #8537)
   = addErrCtxt (spec_ctxt prag) $
-    do  { warnIf (not (isOverloadedTy poly_ty || isInlinePragma inl))
+    do  { warnIf' (not (isOverloadedTy poly_ty || isInlinePragma inl))
                  (text "SPECIALISE pragma for non-overloaded function"
                   <+> quotes (ppr fun_name))
                   -- Note [SPECIALISE pragmas]
@@ -1206,7 +1208,7 @@ tcImpSpec :: (Name, Sig Name) -> TcM [TcSpecPrag]
 tcImpSpec (name, prag)
  = do { id <- tcLookupId name
       ; unless (isAnyInlinePragma (idInlinePragma id))
-               (addWarnTc (impSpecErr name))
+               (addWarnTc' (impSpecErr name))
       ; tcSpecPrag id prag }
 
 impSpecErr :: Name -> SDoc
diff --git a/compiler/typecheck/TcClassDcl.hs b/compiler/typecheck/TcClassDcl.hs
index b1baabb963..3ccebeff0c 100644
--- a/compiler/typecheck/TcClassDcl.hs
+++ b/compiler/typecheck/TcClassDcl.hs
@@ -210,9 +210,9 @@ tcDefMeth clas tyvars this_dict binds_in hs_sig_fn prag_fn
 
        ; spec_prags <- discardConstraints $
                        tcSpecPrags global_dm_id prags
-       ; warnTc (not (null spec_prags))
-                (text "Ignoring SPECIALISE pragmas on default method"
-                 <+> quotes (ppr sel_name))
+       ; warnTc' (not (null spec_prags))
+                 (text "Ignoring SPECIALISE pragmas on default method"
+                  <+> quotes (ppr sel_name))
 
        ; let hs_ty = lookupHsSig hs_sig_fn sel_name
                      `orElse` pprPanic "tc_dm" (ppr sel_name)
@@ -280,7 +280,7 @@ tcClassMinimalDef _clas sigs op_info
         -- class ops without default methods are required, since we
         -- have no way to fill them in otherwise
         whenIsJust (isUnsatisfied (mindef `impliesAtom`) defMindef) $
-                   (\bf -> addWarnTc (warningMinimalDefIncomplete bf))
+                   (\bf -> addWarnTc' (warningMinimalDefIncomplete bf))
         return mindef
   where
     -- By default require all methods without a default
@@ -487,7 +487,7 @@ warnMissingAT :: Name -> TcM ()
 warnMissingAT name
   = do { warn <- woptM Opt_WarnMissingMethods
        ; traceTc "warn" (ppr name <+> ppr warn)
-       ; warnTc warn  -- Warn only if -Wmissing-methods
+       ; warnTc Opt_WarnMissingMethods warn  -- Warn only if -Wmissing-methods
                 (text "No explicit" <+> text "associated type"
                     <+> text "or default declaration for     "
                     <+> quotes (ppr name)) }
diff --git a/compiler/typecheck/TcDeriv.hs b/compiler/typecheck/TcDeriv.hs
index 56772f2b1a..2c205069da 100644
--- a/compiler/typecheck/TcDeriv.hs
+++ b/compiler/typecheck/TcDeriv.hs
@@ -559,7 +559,7 @@ deriveStandalone (L loc (DerivDecl deriv_ty overlap_mode))
 warnUselessTypeable :: TcM ()
 warnUselessTypeable
   = do { warn <- woptM Opt_WarnDerivingTypeable
-       ; when warn $ addWarnTc
+       ; when warn $ addWarnTc Opt_WarnDerivingTypeable
                    $ text "Deriving" <+> quotes (ppr typeableClassName) <+>
                      text "has no effect: all types now auto-derive Typeable" }
 
@@ -1499,8 +1499,8 @@ mkNewTypeEqn dflags overlap_mode tvs
 
       -- CanDerive/DerivableViaInstance
       _ -> do when (newtype_deriving && deriveAnyClass) $
-                addWarnTc (sep [ text "Both DeriveAnyClass and GeneralizedNewtypeDeriving are enabled"
-                               , text "Defaulting to the DeriveAnyClass strategy for instantiating" <+> ppr cls ])
+                addWarnTc' (sep [ text "Both DeriveAnyClass and GeneralizedNewtypeDeriving are enabled"
+                                , text "Defaulting to the DeriveAnyClass strategy for instantiating" <+> ppr cls ])
               go_for_it
   where
         newtype_deriving  = xopt LangExt.GeneralizedNewtypeDeriving dflags
diff --git a/compiler/typecheck/TcErrors.hs b/compiler/typecheck/TcErrors.hs
index 2140a797ff..75a3b5cbb7 100644
--- a/compiler/typecheck/TcErrors.hs
+++ b/compiler/typecheck/TcErrors.hs
@@ -342,13 +342,13 @@ warnRedundantConstraints ctxt env info ev_vars
    addErrCtxt (text "In" <+> ppr info) $
    do { env <- getLclEnv
       ; msg <- mkErrorReport ctxt env (important doc)
-      ; reportWarning msg }
+      ; reportWarning Nothing msg }
 
  | otherwise  -- But for InstSkol there already *is* a surrounding
               -- "In the instance declaration for Eq [a]" context
               -- and we don't want to say it twice. Seems a bit ad-hoc
  = do { msg <- mkErrorReport ctxt env (important doc)
-      ; reportWarning msg }
+      ; reportWarning Nothing msg }
  where
    doc = text "Redundant constraint" <> plural redundant_evs <> colon
          <+> pprEvVarTheta redundant_evs
@@ -573,7 +573,7 @@ reportGroup mk_err ctxt cts =
         -- Only warn about missing MonadFail constraint when
         -- there are no other missing contstraints!
         (monadFailCts, []) -> do { err <- mk_err ctxt monadFailCts
-                                 ; reportWarning err }
+                                 ; reportWarning Nothing err }
 
         (_, cts') -> do { err <- mk_err ctxt cts'
                         ; maybeReportError ctxt err
@@ -597,7 +597,7 @@ maybeReportHoleError ctxt ct err
     -- only if -fwarn_partial_type_signatures is on
     case cec_type_holes ctxt of
        HoleError -> reportError err
-       HoleWarn  -> reportWarning err
+       HoleWarn  -> reportWarning (Just Opt_WarnPartialTypeSignatures) err
        HoleDefer -> return ()
 
   -- Otherwise this is a typed hole in an expression
@@ -605,7 +605,7 @@ maybeReportHoleError ctxt ct err
   = -- If deferring, report a warning only if -Wtyped-holds is on
     case cec_expr_holes ctxt of
        HoleError -> reportError err
-       HoleWarn  -> reportWarning err
+       HoleWarn  -> reportWarning (Just Opt_WarnTypedHoles) err
        HoleDefer -> return ()
 
 maybeReportError :: ReportErrCtxt -> ErrMsg -> TcM ()
@@ -615,12 +615,12 @@ maybeReportError ctxt err
   = return ()            -- so suppress this error/warning
 
   | cec_errors_as_warns ctxt
-  = reportWarning err
+  = reportWarning Nothing err
 
   | otherwise
   = case cec_defer_type_errors ctxt of
       TypeDefer -> return ()
-      TypeWarn  -> reportWarning err
+      TypeWarn  -> reportWarning Nothing err
       TypeError -> reportError err
 
 addDeferredBinding :: ReportErrCtxt -> ErrMsg -> Ct -> TcM ()
@@ -2328,7 +2328,7 @@ warnDefaulting wanteds default_ty
                            , quotes (ppr default_ty) ])
                      2
                      ppr_wanteds
-       ; setCtLocM loc $ warnTc warn_default warn_msg }
+       ; setCtLocM loc $ warnTc Opt_WarnTypeDefaults warn_default warn_msg }
 
 {-
 Note [Runtime skolems]
diff --git a/compiler/typecheck/TcExpr.hs b/compiler/typecheck/TcExpr.hs
index d54fbc7644..025d376e77 100644
--- a/compiler/typecheck/TcExpr.hs
+++ b/compiler/typecheck/TcExpr.hs
@@ -2221,7 +2221,8 @@ checkMissingFields con_like rbinds
 
     warn <- woptM Opt_WarnMissingFields
     unless (not (warn && notNull missing_ns_fields))
-           (warnTc True (missingFields con_like missing_ns_fields))
+           (warnTc Opt_WarnMissingFields True
+               (missingFields con_like missing_ns_fields))
 
   where
     missing_s_fields
diff --git a/compiler/typecheck/TcForeign.hs b/compiler/typecheck/TcForeign.hs
index bc3a9283c6..bca9a5603d 100644
--- a/compiler/typecheck/TcForeign.hs
+++ b/compiler/typecheck/TcForeign.hs
@@ -349,7 +349,8 @@ checkMissingAmpersand :: DynFlags -> [Type] -> Type -> TcM ()
 checkMissingAmpersand dflags arg_tys res_ty
   | null arg_tys && isFunPtrTy res_ty &&
     wopt Opt_WarnDodgyForeignImports dflags
-  = addWarn (text "possible missing & in foreign import of FunPtr")
+  = addWarn Opt_WarnDodgyForeignImports
+        (text "possible missing & in foreign import of FunPtr")
   | otherwise
   = return ()
 
@@ -522,7 +523,8 @@ checkCConv StdCallConv  = do dflags <- getDynFlags
                                  then return StdCallConv
                                  else do -- This is a warning, not an error. see #3336
                                          when (wopt Opt_WarnUnsupportedCallingConventions dflags) $
-                                             addWarnTc (text "the 'stdcall' calling convention is unsupported on this platform," $$ text "treating as ccall")
+                                             addWarnTc Opt_WarnUnsupportedCallingConventions
+                                                 (text "the 'stdcall' calling convention is unsupported on this platform," $$ text "treating as ccall")
                                          return CCallConv
 checkCConv PrimCallConv = do addErrTc (text "The `prim' calling convention can only be used with `foreign import'")
                              return PrimCallConv
diff --git a/compiler/typecheck/TcInstDcls.hs b/compiler/typecheck/TcInstDcls.hs
index 82c66cc953..5b433860bd 100644
--- a/compiler/typecheck/TcInstDcls.hs
+++ b/compiler/typecheck/TcInstDcls.hs
@@ -447,7 +447,7 @@ tcInstDecls1 tycl_decls inst_decls deriv_decls
            if isHsBootOrSig (tcg_src env)
              then
                do warn <- woptM Opt_WarnDerivingTypeable
-                  when warn $ addWarnTc $ vcat
+                  when warn $ addWarnTc Opt_WarnDerivingTypeable $ vcat
                     [ ppTypeable <+> text "instances in .hs-boot files are ignored"
                     , text "This warning will become an error in future versions of the compiler"
                     ]
@@ -1570,7 +1570,7 @@ derivBindCtxt sel_id clas tys
 warnUnsatisfiedMinimalDefinition :: ClassMinimalDef -> TcM ()
 warnUnsatisfiedMinimalDefinition mindef
   = do { warn <- woptM Opt_WarnMissingMethods
-       ; warnTc warn message
+       ; warnTc Opt_WarnMissingMethods warn message
        }
   where
     message = vcat [text "No explicit implementation for"
diff --git a/compiler/typecheck/TcMatches.hs b/compiler/typecheck/TcMatches.hs
index 5f3bc5b73a..0070cb79c6 100644
--- a/compiler/typecheck/TcMatches.hs
+++ b/compiler/typecheck/TcMatches.hs
@@ -975,7 +975,8 @@ emitMonadFailConstraint pat res_ty
        ; return () }
 
 warnRebindableClash :: LPat TcId -> TcRn ()
-warnRebindableClash pattern = addWarnAt (getLoc pattern)
+warnRebindableClash pattern = addWarnAt Opt_WarnMissingMonadFailInstances
+    (getLoc pattern)
     (text "The failable pattern" <+> quotes (ppr pattern)
      $$
      nest 2 (text "is used together with -XRebindableSyntax."
diff --git a/compiler/typecheck/TcPat.hs b/compiler/typecheck/TcPat.hs
index 4d1d09a32f..4eaaa58fc9 100644
--- a/compiler/typecheck/TcPat.hs
+++ b/compiler/typecheck/TcPat.hs
@@ -219,7 +219,7 @@ addInlinePrags poly_id prags
          warn_multiple_inlines inl2 inls
        | otherwise
        = setSrcSpan loc $
-         addWarnTc (hang (text "Multiple INLINE pragmas for" <+> ppr poly_id)
+         addWarnTc' (hang (text "Multiple INLINE pragmas for" <+> ppr poly_id)
                        2 (vcat (text "Ignoring all but the first"
                                 : map pp_inl (inl1:inl2:inls))))
 
diff --git a/compiler/typecheck/TcRnDriver.hs b/compiler/typecheck/TcRnDriver.hs
index fdc6e5e638..385405f6a7 100644
--- a/compiler/typecheck/TcRnDriver.hs
+++ b/compiler/typecheck/TcRnDriver.hs
@@ -310,7 +310,8 @@ tcRnModuleTcRnM hsc_env hsc_src
                                          implicit_prelude import_decls } ;
 
         whenWOptM Opt_WarnImplicitPrelude $
-             when (notNull prel_imports) $ addWarn (implicitPreludeWarn) ;
+             when (notNull prel_imports) $
+                  addWarn Opt_WarnImplicitPrelude (implicitPreludeWarn) ;
 
         tcg_env <- {-# SCC "tcRnImports" #-}
                    tcRnImports hsc_env (prel_imports ++ import_decls) ;
@@ -1286,7 +1287,7 @@ tcPreludeClashWarn warnFlag name = do
     ; traceTc "tcPreludeClashWarn/prelude_functions"
                 (hang (ppr name) 4 (sep [ppr clashingElts]))
 
-    ; let warn_msg x = addWarnAt (nameSrcSpan (gre_name x)) (hsep
+    ; let warn_msg x = addWarnAt warnFlag (nameSrcSpan (gre_name x)) (hsep
               [ text "Local definition of"
               , (quotes . ppr . nameOccName . gre_name) x
               , text "clashes with a future Prelude name." ]
@@ -1397,7 +1398,7 @@ tcMissingParentClassWarn warnFlag isName shouldName
            -- <should>" e.g. "Foo is an instance of Monad but not Applicative"
            ; let instLoc = srcLocSpan . nameSrcLoc $ getName isInst
                  warnMsg (Just name:_) =
-                      addWarnAt instLoc $
+                      addWarnAt warnFlag instLoc $
                            hsep [ (quotes . ppr . nameOccName) name
                                 , text "is an instance of"
                                 , (ppr . nameOccName . className) isClass
diff --git a/compiler/typecheck/TcRnMonad.hs b/compiler/typecheck/TcRnMonad.hs
index 8cf0d748e3..1db87e4602 100644
--- a/compiler/typecheck/TcRnMonad.hs
+++ b/compiler/typecheck/TcRnMonad.hs
@@ -719,9 +719,13 @@ checkErr :: Bool -> MsgDoc -> TcRn ()
 -- Add the error if the bool is False
 checkErr ok msg = unless ok (addErr msg)
 
-warnIf :: Bool -> MsgDoc -> TcRn ()
-warnIf True  msg = addWarn msg
-warnIf False _   = return ()
+warnIf :: WarningFlag -> Bool -> MsgDoc -> TcRn ()
+warnIf flag True  msg = addWarn flag msg
+warnIf _    False _   = return ()
+
+warnIf' :: Bool -> MsgDoc -> TcRn ()
+warnIf' True  msg = addWarn' msg
+warnIf' False _   = return ()
 
 addMessages :: Messages -> TcRn ()
 addMessages msgs1
@@ -777,9 +781,9 @@ reportError err
          (warns, errs) <- readTcRef errs_var ;
          writeTcRef errs_var (warns, errs `snocBag` err) }
 
-reportWarning :: ErrMsg -> TcRn ()
-reportWarning err
-  = do { let warn = makeIntoWarning err
+reportWarning :: Maybe WarningFlag -> ErrMsg -> TcRn ()
+reportWarning flag err
+  = do { let warn = makeIntoWarning flag err
                     -- 'err' was built by mkLongErrMsg or something like that,
                     -- so it's of error severity.  For a warning we downgrade
                     -- its severity to SevWarning
@@ -1081,44 +1085,70 @@ failIfTcM True  err = failWithTcM err
 
 --         Warnings have no 'M' variant, nor failure
 
-warnTc :: Bool -> MsgDoc -> TcM ()
-warnTc warn_if_true warn_msg
-  | warn_if_true = addWarnTc warn_msg
+warnTc :: WarningFlag -> Bool -> MsgDoc -> TcM ()
+warnTc flag warn_if_true warn_msg
+  | warn_if_true = addWarnTc flag warn_msg
+  | otherwise    = return ()
+
+warnTc' :: Bool -> MsgDoc -> TcM ()
+warnTc' warn_if_true warn_msg
+  | warn_if_true = addWarnTc' warn_msg
   | otherwise    = return ()
 
-warnTcM :: Bool -> (TidyEnv, MsgDoc) -> TcM ()
-warnTcM warn_if_true warn_msg
-  | warn_if_true = addWarnTcM warn_msg
+warnTcM :: WarningFlag -> Bool -> (TidyEnv, MsgDoc) -> TcM ()
+warnTcM flag warn_if_true warn_msg
+  | warn_if_true = addWarnTcM flag warn_msg
   | otherwise    = return ()
 
-addWarnTc :: MsgDoc -> TcM ()
-addWarnTc msg = do { env0 <- tcInitTidyEnv
-                   ; addWarnTcM (env0, msg) }
+warnTcM' :: Bool -> (TidyEnv, MsgDoc) -> TcM ()
+warnTcM' warn_if_true warn_msg
+  | warn_if_true = addWarnTcM' warn_msg
+  | otherwise    = return ()
+
+addWarnTc :: WarningFlag -> MsgDoc -> TcM ()
+addWarnTc flag msg = do { env0 <- tcInitTidyEnv
+                   ; addWarnTcM flag (env0, msg) }
+
+addWarnTc' :: MsgDoc -> TcM ()
+addWarnTc' msg = do { env0 <- tcInitTidyEnv
+                   ; addWarnTcM' (env0, msg) }
 
-addWarnTcM :: (TidyEnv, MsgDoc) -> TcM ()
-addWarnTcM (env0, msg)
+addWarnTcM :: WarningFlag -> (TidyEnv, MsgDoc) -> TcM ()
+addWarnTcM flag (env0, msg)
  = do { ctxt <- getErrCtxt ;
         err_info <- mkErrInfo env0 ctxt ;
-        add_warn msg err_info }
+        add_warn (Just flag) msg err_info }
+
+addWarnTcM' :: (TidyEnv, MsgDoc) -> TcM ()
+addWarnTcM' (env0, msg)
+ = do { ctxt <- getErrCtxt ;
+        err_info <- mkErrInfo env0 ctxt ;
+        add_warn Nothing msg err_info }
+
+addWarn :: WarningFlag -> MsgDoc -> TcRn ()
+addWarn flag msg = add_warn (Just flag) msg Outputable.empty
+
+addWarn' :: MsgDoc -> TcRn ()
+addWarn' msg = add_warn Nothing msg Outputable.empty
 
-addWarn :: MsgDoc -> TcRn ()
-addWarn msg = add_warn msg Outputable.empty
+addWarnAt :: WarningFlag -> SrcSpan -> MsgDoc -> TcRn ()
+addWarnAt flag loc msg = add_warn_at (Just flag) loc msg Outputable.empty
 
-addWarnAt :: SrcSpan -> MsgDoc -> TcRn ()
-addWarnAt loc msg = add_warn_at loc msg Outputable.empty
+addWarnAt' :: SrcSpan -> MsgDoc -> TcRn ()
+addWarnAt' loc msg = add_warn_at Nothing loc msg Outputable.empty
 
-add_warn :: MsgDoc -> MsgDoc -> TcRn ()
-add_warn msg extra_info
+add_warn :: Maybe WarningFlag -> MsgDoc -> MsgDoc -> TcRn ()
+add_warn flag msg extra_info
   = do { loc <- getSrcSpanM
-       ; add_warn_at loc msg extra_info }
+       ; add_warn_at flag loc msg extra_info }
 
-add_warn_at :: SrcSpan -> MsgDoc -> MsgDoc -> TcRn ()
-add_warn_at loc msg extra_info
+add_warn_at :: Maybe WarningFlag -> SrcSpan -> MsgDoc -> MsgDoc -> TcRn ()
+add_warn_at flag loc msg extra_info
   = do { dflags <- getDynFlags ;
          printer <- getPrintUnqualified dflags ;
          let { warn = mkLongWarnMsg dflags loc printer
                                     msg extra_info } ;
-         reportWarning warn }
+         reportWarning flag warn }
 
 tcInitTidyEnv :: TcM TidyEnv
 tcInitTidyEnv
@@ -1486,7 +1516,8 @@ failIfM msg
   = do  { env <- getLclEnv
         ; let full_msg = (if_loc env <> colon) $$ nest 2 msg
         ; dflags <- getDynFlags
-        ; liftIO (log_action dflags dflags SevFatal noSrcSpan (defaultErrStyle dflags) full_msg)
+        ; liftIO (log_action dflags dflags Nothing SevFatal
+                   noSrcSpan (defaultErrStyle dflags) full_msg)
         ; failM }
 
 --------------------
@@ -1522,7 +1553,8 @@ forkM_maybe doc thing_inside
                           dflags <- getDynFlags
                           let msg = hang (text "forkM failed:" <+> doc)
                                        2 (text (show exn))
-                          liftIO $ log_action dflags dflags SevFatal noSrcSpan (defaultErrStyle dflags) msg
+                          liftIO $ log_action dflags dflags Nothing SevFatal
+                                     noSrcSpan (defaultErrStyle dflags) msg
 
                     ; traceIf (text "} ending fork (badly)" <+> doc)
                     ; return Nothing }
diff --git a/compiler/typecheck/TcSMonad.hs b/compiler/typecheck/TcSMonad.hs
index 053c53b86a..08a0bd87dc 100644
--- a/compiler/typecheck/TcSMonad.hs
+++ b/compiler/typecheck/TcSMonad.hs
@@ -2351,9 +2351,10 @@ wrapWarnTcS :: TcM a -> TcS a
 wrapWarnTcS = wrapTcS
 
 failTcS, panicTcS  :: SDoc -> TcS a
-warnTcS, addErrTcS :: SDoc -> TcS ()
+warnTcS   :: WarningFlag -> SDoc -> TcS ()
+addErrTcS :: SDoc -> TcS ()
 failTcS      = wrapTcS . TcM.failWith
-warnTcS      = wrapTcS . TcM.addWarn
+warnTcS flag = wrapTcS . TcM.addWarn flag
 addErrTcS    = wrapTcS . TcM.addErr
 panicTcS doc = pprPanic "TcCanonical" doc
 
diff --git a/compiler/typecheck/TcSimplify.hs b/compiler/typecheck/TcSimplify.hs
index be0735816b..bb86482590 100644
--- a/compiler/typecheck/TcSimplify.hs
+++ b/compiler/typecheck/TcSimplify.hs
@@ -742,7 +742,7 @@ decideQuantification apply_mr sigs name_taus constraints
            -- Warn about the monomorphism restriction
        ; warn_mono <- woptM Opt_WarnMonomorphism
        ; let mr_bites = constrained_tvs `intersectsVarSet` zonked_tkvs
-       ; warnTc (warn_mono && mr_bites) $
+       ; warnTc Opt_WarnMonomorphism (warn_mono && mr_bites) $
          hang (text "The Monomorphism Restriction applies to the binding"
                <> plural bndrs <+> text "for" <+> pp_bndrs)
              2 (text "Consider giving a type signature for"
diff --git a/compiler/typecheck/TcSplice.hs b/compiler/typecheck/TcSplice.hs
index 921da07d2d..6ea4fa3bc5 100644
--- a/compiler/typecheck/TcSplice.hs
+++ b/compiler/typecheck/TcSplice.hs
@@ -806,8 +806,8 @@ instance TH.Quasi TcM where
 
   -- 'msg' is forced to ensure exceptions don't escape,
   -- see Note [Exceptions in TH]
-  qReport True msg  = seqList msg $ addErr  (text msg)
-  qReport False msg = seqList msg $ addWarn (text msg)
+  qReport True msg  = seqList msg $ addErr   (text msg)
+  qReport False msg = seqList msg $ addWarn' (text msg)
 
   qLocation = do { m <- getModule
                  ; l <- getSrcSpanM
diff --git a/compiler/typecheck/TcTyClsDecls.hs b/compiler/typecheck/TcTyClsDecls.hs
index e68efd09f9..e550fe0eb4 100644
--- a/compiler/typecheck/TcTyClsDecls.hs
+++ b/compiler/typecheck/TcTyClsDecls.hs
@@ -2125,13 +2125,13 @@ checkValidDataCon dflags existential_ok tc con
           (bad_bang n (text "Lazy annotation (~) without StrictData"))
     check_bang (HsSrcBang _ want_unpack strict_mark) rep_bang n
       | isSrcUnpacked want_unpack, not is_strict
-      = addWarnTc (bad_bang n (text "UNPACK pragma lacks '!'"))
+      = addWarnTc' (bad_bang n (text "UNPACK pragma lacks '!'"))
       | isSrcUnpacked want_unpack
       , case rep_bang of { HsUnpack {} -> False; _ -> True }
       , not (gopt Opt_OmitInterfacePragmas dflags)
            -- If not optimising, se don't unpack, so don't complain!
            -- See MkId.dataConArgRep, the (HsBang True) case
-      = addWarnTc (bad_bang n (text "Ignoring unusable UNPACK pragma"))
+      = addWarnTc' (bad_bang n (text "Ignoring unusable UNPACK pragma"))
       where
         is_strict = case strict_mark of
                       NoSrcStrict -> xopt LangExt.StrictData dflags
diff --git a/compiler/typecheck/TcValidity.hs b/compiler/typecheck/TcValidity.hs
index 56cb348669..b018b52994 100644
--- a/compiler/typecheck/TcValidity.hs
+++ b/compiler/typecheck/TcValidity.hs
@@ -684,7 +684,8 @@ check_valid_theta _ _ []
   = return ()
 check_valid_theta env ctxt theta
   = do { dflags <- getDynFlags
-       ; warnTcM (wopt Opt_WarnDuplicateConstraints dflags &&
+       ; warnTcM Opt_WarnDuplicateConstraints
+                 (wopt Opt_WarnDuplicateConstraints dflags &&
                   notNull dups) (dupPredWarn env dups)
        ; traceTc "check_valid_theta" (ppr theta)
        ; mapM_ (check_pred_ty env dflags ctxt) theta }
@@ -1455,7 +1456,7 @@ checkValidCoAxiom ax@(CoAxiom { co_ax_tc = fam_tc, co_ax_branches = branches })
     --   (b) failure of injectivity
     check_branch_compat prev_branches cur_branch
       | cur_branch `isDominatedBy` prev_branches
-      = do { addWarnAt (coAxBranchSpan cur_branch) $
+      = do { addWarnAt' (coAxBranchSpan cur_branch) $
              inaccessibleCoAxBranch ax cur_branch
            ; return prev_branches }
       | otherwise