path: root/compiler/main/ErrUtils.hs

{-
(c) The AQUA Project, Glasgow University, 1994-1998

\section[ErrsUtils]{Utilities for error reporting}
-}

{-# LANGUAGE CPP #-}
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE RecordWildCards #-}

module ErrUtils (
        -- * Basic types
        Validity(..), andValid, allValid, isValid, getInvalids,
        Severity(..),

        -- * Messages
        ErrMsg, errMsgDoc,
        ErrDoc, errDoc, errDocImportant, errDocContext, errDocSupplementary,
        WarnMsg, MsgDoc,
        Messages, ErrorMessages, WarningMessages,
        unionMessages,
        errMsgSpan, errMsgContext,
        errorsFound, isEmptyMessages,
        isWarnMsgFatal,

        -- ** Formatting
        pprMessageBag, pprErrMsgBagWithLoc,
        pprLocErrMsg, printBagOfErrors,
        formatErrDoc,

        -- ** Construction
        emptyMessages, mkLocMessage, mkLocMessageAnn, makeIntoWarning,
        mkErrMsg, mkPlainErrMsg, mkErrDoc, mkLongErrMsg, mkWarnMsg,
        mkPlainWarnMsg,
        warnIsErrorMsg, mkLongWarnMsg,

        -- * Utilities
        doIfSet, doIfSet_dyn,
        getCaretDiagnostic,

        -- * Dump files
        dumpIfSet, dumpIfSet_dyn, dumpIfSet_dyn_printer,
        mkDumpDoc, dumpSDoc,

        -- * Issuing messages during compilation
        putMsg, printInfoForUser, printOutputForUser,
        logInfo, logOutput,
        errorMsg, warningMsg,
        fatalErrorMsg, fatalErrorMsg'',
        compilationProgressMsg,
        showPass, withTiming,
        debugTraceMsg,
        ghcExit,
        prettyPrintGhcErrors,
    ) where

#include "HsVersions.h"

import Bag
import Exception
import Outputable
import Panic
import qualified PprColour as Col
import SrcLoc
import DynFlags
import FastString (unpackFS)
import StringBuffer (hGetStringBuffer, len, lexemeToString)
import Json

import System.Directory
import System.Exit      ( ExitCode(..), exitWith )
import System.FilePath  ( takeDirectory, (</>) )
import Data.List
import qualified Data.Set as Set
import Data.IORef
import Data.Maybe       ( fromMaybe )
import Data.Ord
import Data.Time
import Control.Monad
import Control.Monad.IO.Class
import System.IO
import System.IO.Error  ( catchIOError )
import GHC.Conc         ( getAllocationCounter )
import System.CPUTime

-------------------------
type MsgDoc  = SDoc

-------------------------
data Validity
  = IsValid            -- ^ Everything is fine
  | NotValid MsgDoc    -- ^ A problem, and some indication of why

isValid :: Validity -> Bool
isValid IsValid       = True
isValid (NotValid {}) = False

andValid :: Validity -> Validity -> Validity
andValid IsValid v = v
andValid v _       = v

-- | If they aren't all valid, return the first
allValid :: [Validity] -> Validity
allValid []       = IsValid
allValid (v : vs) = v `andValid` allValid vs

getInvalids :: [Validity] -> [MsgDoc]
getInvalids vs = [d | NotValid d <- vs]

-- -----------------------------------------------------------------------------
-- Basic error messages: just render a message with a source location.

type Messages        = (WarningMessages, ErrorMessages)
type WarningMessages = Bag WarnMsg
type ErrorMessages   = Bag ErrMsg

unionMessages :: Messages -> Messages -> Messages
unionMessages (warns1, errs1) (warns2, errs2) =
  (warns1 `unionBags` warns2, errs1 `unionBags` errs2)

data ErrMsg = ErrMsg {
        errMsgSpan        :: SrcSpan,
        errMsgContext     :: PrintUnqualified,
        errMsgDoc         :: ErrDoc,
        -- | This has the same text as errDocImportant . errMsgDoc.
        errMsgShortString :: String,
        errMsgSeverity    :: Severity,
        errMsgReason      :: WarnReason
        }
        -- The SrcSpan is used for sorting errors into line-number order


-- | Categorise error msgs by their importance.  This is so each section can
-- be rendered visually distinct.  See Note [Error report] for where these come
-- from.
data ErrDoc = ErrDoc {
        -- | Primary error msg.
        errDocImportant     :: [MsgDoc],
        -- | Context e.g. \"In the second argument of ...\".
        errDocContext       :: [MsgDoc],
        -- | Supplementary information, e.g. \"Relevant bindings include ...\".
        errDocSupplementary :: [MsgDoc]
        }

errDoc :: [MsgDoc] -> [MsgDoc] -> [MsgDoc] -> ErrDoc
errDoc = ErrDoc

type WarnMsg = ErrMsg

data Severity
  = SevOutput
  | SevFatal
  | SevInteractive

  | SevDump
    -- ^ Log messagse intended for compiler developers
    -- No file/line/column stuff

  | SevInfo
    -- ^ Log messages intended for end users.
    -- No file/line/column stuff.

  | SevWarning
  | SevError
    -- ^ SevWarning and SevError are used for warnings and errors
    --   o The message has a file/line/column heading,
    --     plus "warning:" or "error:",
    --     added by mkLocMessags
    --   o Output is intended for end users
  deriving Show


instance ToJson Severity where
  json s = JSString (show s)


instance Show ErrMsg where
    show em = errMsgShortString em

pprMessageBag :: Bag MsgDoc -> SDoc
pprMessageBag msgs = vcat (punctuate blankLine (bagToList msgs))

-- | Make an unannotated error message with location info.
mkLocMessage :: Severity -> SrcSpan -> MsgDoc -> MsgDoc
mkLocMessage = mkLocMessageAnn Nothing

-- | Make a possibly annotated error message with location info.
mkLocMessageAnn
  :: Maybe String                       -- ^ optional annotation
  -> Severity                           -- ^ severity
  -> SrcSpan                            -- ^ location
  -> MsgDoc                             -- ^ message
  -> 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>".
mkLocMessageAnn ann severity locn msg
    = sdocWithDynFlags $ \dflags ->
      let locn' = if gopt Opt_ErrorSpans dflags
                  then ppr locn
                  else ppr (srcSpanStart locn)

          sevColour = getSeverityColour severity (colScheme dflags)

          -- Add optional information
          optAnn = case ann of
            Nothing -> text ""
            Just i  -> text " [" <> coloured sevColour (text i) <> text "]"

          -- Add prefixes, like    Foo.hs:34: warning:
          --                           <the warning message>
          prefix = locn' <> colon <+>
                   coloured sevColour sevText <> optAnn

      in coloured (Col.sMessage (colScheme dflags)) (hang prefix 4 msg)

  where
    sevText =
      case severity of
        SevWarning -> text "warning:"
        SevError   -> text "error:"
        SevFatal   -> text "fatal:"
        _          -> empty

getSeverityColour :: Severity -> Col.Scheme -> Col.PprColour
getSeverityColour SevWarning = Col.sWarning
getSeverityColour SevError   = Col.sError
getSeverityColour SevFatal   = Col.sFatal
getSeverityColour _          = const mempty

getCaretDiagnostic :: Severity -> SrcSpan -> IO MsgDoc
getCaretDiagnostic _ (UnhelpfulSpan _) = pure empty
getCaretDiagnostic severity (RealSrcSpan span) = do
  caretDiagnostic <$> getSrcLine (srcSpanFile span) (row - 1)

  where

    getSrcLine fn i = do
      (getLine i <$> readFile' (unpackFS fn))
        `catchIOError` \ _ ->
          pure Nothing

    getLine i contents =
      case drop i (lines contents) of
        srcLine : _ -> Just srcLine
        [] -> Nothing

    readFile' fn = do
      -- StringBuffer has advantages over readFile:
      -- (a) no lazy IO, otherwise IO exceptions may occur in pure code
      -- (b) always UTF-8, rather than some system-dependent encoding
      --     (Haskell source code must be UTF-8 anyway)
      buf <- hGetStringBuffer fn
      pure (fix <$> lexemeToString buf (len buf))

    -- allow user to visibly see that their code is incorrectly encoded
    -- (StringBuffer.nextChar uses \0 to represent undecodable characters)
    fix '\0' = '\xfffd'
    fix c    = c

    row = srcSpanStartLine span
    rowStr = show row
    multiline = row /= srcSpanEndLine span

    stripNewlines = filter (/= '\n')

    caretDiagnostic Nothing = empty
    caretDiagnostic (Just srcLineWithNewline) =
      sdocWithDynFlags $ \ dflags ->
      let sevColour = getSeverityColour severity (colScheme dflags)
          marginColour = Col.sMargin (colScheme dflags)
      in
      coloured marginColour (text marginSpace) <>
      text ("\n") <>
      coloured marginColour (text marginRow) <>
      text (" " ++ srcLinePre) <>
      coloured sevColour (text srcLineSpan) <>
      text (srcLinePost ++ "\n") <>
      coloured marginColour (text marginSpace) <>
      coloured sevColour (text (" " ++ caretLine))

      where

        srcLine = stripNewlines srcLineWithNewline

        start = srcSpanStartCol span - 1
        end | multiline = length srcLine
            | otherwise = srcSpanEndCol span - 1
        width = max 1 (end - start)

        marginWidth = length rowStr
        marginSpace = replicate marginWidth ' ' ++ " |"
        marginRow   = rowStr ++ " |"

        (srcLinePre,  srcLineRest) = splitAt start srcLine
        (srcLineSpan, srcLinePost) = splitAt width srcLineRest

        caretEllipsis | multiline = "..."
                      | otherwise = ""
        caretLine = replicate start ' ' ++ replicate width '^' ++ caretEllipsis

makeIntoWarning :: WarnReason -> ErrMsg -> ErrMsg
makeIntoWarning reason err = err
    { errMsgSeverity = SevWarning
    , errMsgReason = reason }

-- -----------------------------------------------------------------------------
-- Collecting up messages for later ordering and printing.

mk_err_msg :: DynFlags -> Severity -> SrcSpan -> PrintUnqualified -> ErrDoc -> ErrMsg
mk_err_msg dflags sev locn print_unqual doc
 = ErrMsg { errMsgSpan = locn
          , errMsgContext = print_unqual
          , errMsgDoc = doc
          , errMsgShortString = showSDoc dflags (vcat (errDocImportant doc))
          , errMsgSeverity = sev
          , errMsgReason = NoReason }

mkErrDoc :: DynFlags -> SrcSpan -> PrintUnqualified -> ErrDoc -> ErrMsg
mkErrDoc dflags = mk_err_msg dflags SevError

mkLongErrMsg, mkLongWarnMsg   :: DynFlags -> SrcSpan -> PrintUnqualified -> MsgDoc -> MsgDoc -> ErrMsg
-- ^ A long (multi-line) error message
mkErrMsg, mkWarnMsg           :: DynFlags -> SrcSpan -> PrintUnqualified -> MsgDoc            -> ErrMsg
-- ^ A short (one-line) error message
mkPlainErrMsg, mkPlainWarnMsg :: DynFlags -> SrcSpan ->                     MsgDoc            -> ErrMsg
-- ^ Variant that doesn't care about qualified/unqualified names

mkLongErrMsg   dflags locn unqual msg extra = mk_err_msg dflags SevError   locn unqual        (ErrDoc [msg] [] [extra])
mkErrMsg       dflags locn unqual msg       = mk_err_msg dflags SevError   locn unqual        (ErrDoc [msg] [] [])
mkPlainErrMsg  dflags locn        msg       = mk_err_msg dflags SevError   locn alwaysQualify (ErrDoc [msg] [] [])
mkLongWarnMsg  dflags locn unqual msg extra = mk_err_msg dflags SevWarning locn unqual        (ErrDoc [msg] [] [extra])
mkWarnMsg      dflags locn unqual msg       = mk_err_msg dflags SevWarning locn unqual        (ErrDoc [msg] [] [])
mkPlainWarnMsg dflags locn        msg       = mk_err_msg dflags SevWarning locn alwaysQualify (ErrDoc [msg] [] [])

----------------
emptyMessages :: Messages
emptyMessages = (emptyBag, emptyBag)

isEmptyMessages :: Messages -> Bool
isEmptyMessages (warns, errs) = isEmptyBag warns && isEmptyBag errs

warnIsErrorMsg :: DynFlags -> ErrMsg
warnIsErrorMsg dflags
    = mkPlainErrMsg dflags noSrcSpan (text "\nFailing due to -Werror.")

errorsFound :: DynFlags -> Messages -> Bool
errorsFound _dflags (_warns, errs) = not (isEmptyBag errs)

printBagOfErrors :: DynFlags -> Bag ErrMsg -> IO ()
printBagOfErrors dflags bag_of_errors
  = sequence_ [ let style = mkErrStyle dflags unqual
                in putLogMsg dflags reason sev s style (formatErrDoc dflags doc)
              | ErrMsg { errMsgSpan      = s,
                         errMsgDoc       = doc,
                         errMsgSeverity  = sev,
                         errMsgReason    = reason,
                         errMsgContext   = unqual } <- sortMsgBag (Just dflags)
                                                                  bag_of_errors ]

formatErrDoc :: DynFlags -> ErrDoc -> SDoc
formatErrDoc dflags (ErrDoc important context supplementary)
  = case msgs of
        [msg] -> vcat msg
        _ -> vcat $ map starred msgs
    where
    msgs = filter (not . null) $ map (filter (not . Outputable.isEmpty dflags))
        [important, context, supplementary]
    starred = (bullet<+>) . vcat

pprErrMsgBagWithLoc :: Bag ErrMsg -> [SDoc]
pprErrMsgBagWithLoc bag = [ pprLocErrMsg item | item <- sortMsgBag Nothing bag ]

pprLocErrMsg :: ErrMsg -> SDoc
pprLocErrMsg (ErrMsg { errMsgSpan      = s
                     , errMsgDoc       = doc
                     , errMsgSeverity  = sev
                     , errMsgContext   = unqual })
  = sdocWithDynFlags $ \dflags ->
    withPprStyle (mkErrStyle dflags unqual) $
    mkLocMessage sev s (formatErrDoc dflags doc)

sortMsgBag :: Maybe DynFlags -> Bag ErrMsg -> [ErrMsg]
sortMsgBag dflags = maybeLimit . sortBy (maybeFlip cmp) . bagToList
  where maybeFlip :: (a -> a -> b) -> (a -> a -> b)
        maybeFlip
          | fromMaybe False (fmap reverseErrors dflags) = flip
          | otherwise                                   = id
        cmp = comparing errMsgSpan
        maybeLimit = case join (fmap maxErrors dflags) of
          Nothing        -> id
          Just err_limit -> take err_limit

ghcExit :: DynFlags -> Int -> IO ()
ghcExit dflags val
  | val == 0  = exitWith ExitSuccess
  | otherwise = do errorMsg dflags (text "\nCompilation had errors\n\n")
                   exitWith (ExitFailure val)

doIfSet :: Bool -> IO () -> IO ()
doIfSet flag action | flag      = action
                    | otherwise = return ()

doIfSet_dyn :: DynFlags -> GeneralFlag -> IO () -> IO()
doIfSet_dyn dflags flag action | gopt flag dflags = action
                               | otherwise        = return ()

-- -----------------------------------------------------------------------------
-- Dumping

dumpIfSet :: DynFlags -> Bool -> String -> SDoc -> IO ()
dumpIfSet dflags flag hdr doc
  | not flag   = return ()
  | otherwise  = putLogMsg  dflags
                            NoReason
                            SevDump
                            noSrcSpan
                            (defaultDumpStyle dflags)
                            (mkDumpDoc hdr doc)

-- | a wrapper around 'dumpSDoc'.
-- First check whether the dump flag is set
-- Do nothing if it is unset
dumpIfSet_dyn :: DynFlags -> DumpFlag -> String -> SDoc -> IO ()
dumpIfSet_dyn dflags flag hdr doc
  = when (dopt flag dflags) $ dumpSDoc dflags alwaysQualify flag hdr doc

-- | a wrapper around 'dumpSDoc'.
-- First check whether the dump flag is set
-- Do nothing if it is unset
--
-- Unlike 'dumpIfSet_dyn',
-- has a printer argument but no header argument
dumpIfSet_dyn_printer :: PrintUnqualified
                      -> DynFlags -> DumpFlag -> SDoc -> IO ()
dumpIfSet_dyn_printer printer dflags flag doc
  = when (dopt flag dflags) $ dumpSDoc dflags printer flag "" doc

mkDumpDoc :: String -> SDoc -> SDoc
mkDumpDoc hdr doc
   = vcat [blankLine,
           line <+> text hdr <+> line,
           doc,
           blankLine]
     where
        line = text (replicate 20 '=')


-- | Write out a dump.
-- If --dump-to-file is set then this goes to a file.
-- otherwise emit to stdout.
--
-- When @hdr@ is empty, we print in a more compact format (no separators and
-- blank lines)
--
-- The 'DumpFlag' is used only to choose the filename to use if @--dump-to-file@
-- is used; it is not used to decide whether to dump the output
dumpSDoc :: DynFlags -> PrintUnqualified -> DumpFlag -> String -> SDoc -> IO ()
dumpSDoc dflags print_unqual flag hdr doc
 = do let mFile = chooseDumpFile dflags flag
          dump_style = mkDumpStyle dflags print_unqual
      case mFile of
            Just fileName
                 -> do
                        let gdref = generatedDumps dflags
                        gd <- readIORef gdref
                        let append = Set.member fileName gd
                            mode = if append then AppendMode else WriteMode
                        unless append $
                            writeIORef gdref (Set.insert fileName gd)
                        createDirectoryIfMissing True (takeDirectory fileName)
                        handle <- openFile fileName mode

                        -- We do not want the dump file to be affected by
                        -- environment variables, but instead to always use
                        -- UTF8. See:
                        -- https://ghc.haskell.org/trac/ghc/ticket/10762
                        hSetEncoding handle utf8

                        doc' <- if null hdr
                                then return doc
                                else do t <- getCurrentTime
                                        let d = text (show t)
                                             $$ blankLine
                                             $$ doc
                                        return $ mkDumpDoc hdr d
                        defaultLogActionHPrintDoc dflags handle doc' dump_style
                        hClose handle

            -- write the dump to stdout
            Nothing -> do
              let (doc', severity)
                    | null hdr  = (doc, SevOutput)
                    | otherwise = (mkDumpDoc hdr doc, SevDump)
              putLogMsg dflags NoReason severity noSrcSpan dump_style doc'


-- | Choose where to put a dump file based on DynFlags
--
chooseDumpFile :: DynFlags -> DumpFlag -> Maybe FilePath
chooseDumpFile dflags flag

        | gopt Opt_DumpToFile dflags || flag == Opt_D_th_dec_file
        , Just prefix <- getPrefix
        = Just $ setDir (prefix ++ (beautifyDumpName flag))

        | otherwise
        = Nothing

        where getPrefix
                 -- dump file location is being forced
                 --      by the --ddump-file-prefix flag.
               | Just prefix <- dumpPrefixForce dflags
                  = Just prefix
                 -- dump file location chosen by DriverPipeline.runPipeline
               | Just prefix <- dumpPrefix dflags
                  = Just prefix
                 -- we haven't got a place to put a dump file.
               | otherwise
                  = Nothing
              setDir f = case dumpDir dflags of
                         Just d  -> d </> f
                         Nothing ->       f

-- | Build a nice file name from name of a 'DumpFlag' constructor
beautifyDumpName :: DumpFlag -> String
beautifyDumpName Opt_D_th_dec_file = "th.hs"
beautifyDumpName flag
 = let str = show flag
       suff = case stripPrefix "Opt_D_" str of
              Just x -> x
              Nothing -> panic ("Bad flag name: " ++ str)
       dash = map (\c -> if c == '_' then '-' else c) suff
   in dash


-- -----------------------------------------------------------------------------
-- Outputting messages from the compiler

-- We want all messages to go through one place, so that we can
-- redirect them if necessary.  For example, when GHC is used as a
-- library we might want to catch all messages that GHC tries to
-- output and do something else with them.

ifVerbose :: DynFlags -> Int -> IO () -> IO ()
ifVerbose dflags val act
  | verbosity dflags >= val = act
  | otherwise               = return ()

errorMsg :: DynFlags -> MsgDoc -> IO ()
errorMsg dflags msg
   = putLogMsg dflags NoReason SevError noSrcSpan (defaultErrStyle dflags) msg

warningMsg :: DynFlags -> MsgDoc -> IO ()
warningMsg dflags msg
   = putLogMsg dflags NoReason SevWarning noSrcSpan (defaultErrStyle dflags) msg

fatalErrorMsg :: DynFlags -> MsgDoc -> IO ()
fatalErrorMsg dflags msg =
    putLogMsg dflags NoReason SevFatal noSrcSpan (defaultErrStyle dflags) msg

fatalErrorMsg'' :: FatalMessager -> String -> IO ()
fatalErrorMsg'' fm msg = fm msg

compilationProgressMsg :: DynFlags -> String -> IO ()
compilationProgressMsg dflags msg
  = ifVerbose dflags 1 $
    logOutput dflags (defaultUserStyle dflags) (text msg)

showPass :: DynFlags -> String -> IO ()
showPass dflags what
  = ifVerbose dflags 2 $
    logInfo dflags (defaultUserStyle dflags) (text "***" <+> text what <> colon)

-- | Time a compilation phase.
--
-- When timings are enabled (e.g. with the @-v2@ flag), the allocations
-- and CPU time used by the phase will be reported to stderr. Consider
-- a typical usage: @withTiming getDynFlags (text "simplify") force pass@.
-- When timings are enabled the following costs are included in the
-- produced accounting,
--
--  - The cost of executing @pass@ to a result @r@ in WHNF
--  - The cost of evaluating @force r@ to WHNF (e.g. @()@)
--
-- The choice of the @force@ function depends upon the amount of forcing
-- desired; the goal here is to ensure that the cost of evaluating the result
-- is, to the greatest extent possible, included in the accounting provided by
-- 'withTiming'. Often the pass already sufficiently forces its result during
-- construction; in this case @const ()@ is a reasonable choice.
-- In other cases, it is necessary to evaluate the result to normal form, in
-- which case something like @Control.DeepSeq.rnf@ is appropriate.
--
-- To avoid adversely affecting compiler performance when timings are not
-- requested, the result is only forced when timings are enabled.
withTiming :: MonadIO m
           => m DynFlags  -- ^ A means of getting a 'DynFlags' (often
                          -- 'getDynFlags' will work here)
           -> SDoc        -- ^ The name of the phase
           -> (a -> ())   -- ^ A function to force the result
                          -- (often either @const ()@ or 'rnf')
           -> m a         -- ^ The body of the phase to be timed
           -> m a
withTiming getDFlags what force_result action
  = do dflags <- getDFlags
       if verbosity dflags >= 2
          then do liftIO $ logInfo dflags (defaultUserStyle dflags)
                         $ text "***" <+> what <> colon
                  alloc0 <- liftIO getAllocationCounter
                  start <- liftIO getCPUTime
                  !r <- action
                  () <- pure $ force_result r
                  end <- liftIO getCPUTime
                  alloc1 <- liftIO getAllocationCounter
                  -- recall that allocation counter counts down
                  let alloc = alloc0 - alloc1
                  liftIO $ logInfo dflags (defaultUserStyle dflags)
                      (text "!!!" <+> what <> colon <+> text "finished in"
                       <+> doublePrec 2 (realToFrac (end - start) * 1e-9)
                       <+> text "milliseconds"
                       <> comma
                       <+> text "allocated"
                       <+> doublePrec 3 (realToFrac alloc / 1024 / 1024)
                       <+> text "megabytes")
                  pure r
           else action

debugTraceMsg :: DynFlags -> Int -> MsgDoc -> IO ()
debugTraceMsg dflags val msg = ifVerbose dflags val $
                               logInfo dflags (defaultDumpStyle dflags) msg
putMsg :: DynFlags -> MsgDoc -> IO ()
putMsg dflags msg = logInfo dflags (defaultUserStyle dflags) msg

printInfoForUser :: DynFlags -> PrintUnqualified -> MsgDoc -> IO ()
printInfoForUser dflags print_unqual msg
  = logInfo dflags (mkUserStyle dflags print_unqual AllTheWay) msg

printOutputForUser :: DynFlags -> PrintUnqualified -> MsgDoc -> IO ()
printOutputForUser dflags print_unqual msg
  = logOutput dflags (mkUserStyle dflags print_unqual AllTheWay) msg

logInfo :: DynFlags -> PprStyle -> MsgDoc -> IO ()
logInfo dflags sty msg
  = putLogMsg dflags NoReason SevInfo noSrcSpan sty msg

logOutput :: DynFlags -> PprStyle -> MsgDoc -> IO ()
-- ^ Like 'logInfo' but with 'SevOutput' rather then 'SevInfo'
logOutput dflags sty msg
  = putLogMsg dflags NoReason SevOutput noSrcSpan sty msg

prettyPrintGhcErrors :: ExceptionMonad m => DynFlags -> m a -> m a
prettyPrintGhcErrors dflags
    = ghandle $ \e -> case e of
                      PprPanic str doc ->
                          pprDebugAndThen dflags panic (text str) doc
                      PprSorry str doc ->
                          pprDebugAndThen dflags sorry (text str) doc
                      PprProgramError str doc ->
                          pprDebugAndThen dflags pgmError (text str) doc
                      _ ->
                          liftIO $ throwIO e

-- | Checks if given 'WarnMsg' is a fatal warning.
isWarnMsgFatal :: DynFlags -> WarnMsg -> Bool
isWarnMsgFatal dflags ErrMsg{errMsgReason = Reason wflag}
  = wopt_fatal wflag dflags
isWarnMsgFatal dflags _ = gopt Opt_WarnIsError dflags