[commit: ghc] ghc-7.10: base: fix #10298 & #7695 (25b8478)

Fri May 29 15:35:50 UTC 2015

It depends on your locale, this explains the different behavior on your
local machine.

The build machine seems to be using an ASCII locale and GHC wants to print
some Unicode characters (the tick and back-tick surrounding types in error
messages). Before this patch, Iconv was used to do the conversion from
Unicode to ASCII. It seems that it replaces the Unicode ticks with ASCII
ticks (i.e. 0xE28098 in UTF-8 into 0x60 and 0xE28099 into 0x27).

If you enter:
cd ghc/testsuite/tests
grep -rn "match expected type" **/*.stderr

You can see that some .stderr have been generated with a ASCII locale and
some others with a UTF-8 locale by looking at the ticks. Are the tests
expecting ASCII output (e.g. driver/T2507) passing on platforms with UTF-8
locales? The output is not equal to the expected one except if it is
converted to ASCII before the comparison.

With this patch, we don't use Iconv to convert from Unicode to ASCII
because it may not be available in some contexts (docker containers,
initramdisk, etc.). Instead we use the UTF-8 encoder to encode ASCII (ASCII
characters are encoded in the same way in ASCII and in UTF-8) and we don't
try to match Unicode only characters to ASCII ones.

Solutions:
1) change our patch to use our method only when Iconv cannot be used.
2) implement the Unicode to ASCII conversion as performed by Iconv
3) change the locale to a UTF-8 one on the build machine ;-)

Sylvain

2015-05-29 3:23 GMT+02:00 Edward Z. Yang <ezyang at mit.edu>:

> This commit broke the HM builds: https://phabricator.haskell.org/B4147
>
> When I validate locally, though, it works fine.
>
> Edward
>
> Excerpts from git's message of 2015-05-28 18:11:07 -0700:
> > Repository : ssh://git@git.haskell.org/ghc
> >
> > On branch  : ghc-7.10
> > Link       :
> http://ghc.haskell.org/trac/ghc/changeset/25b84781ed950d59c7bffb77a576d3c43a883ca9/ghc
> >
> > >---------------------------------------------------------------
> >
> > commit 25b84781ed950d59c7bffb77a576d3c43a883ca9
> > Author: Austin Seipp <austin at well-typed.com>
> > Date:   Tue May 19 04:56:40 2015 -0500
> >
> >     base: fix #10298 & #7695
> >
> >     Summary:
> >     This applies a patch from Reid Barton and Sylvain Henry, which fix a
> >     disasterous infinite loop when iconv fails to load locale files, as
> >     specified in #10298.
> >
> >     The fix is a bit of a hack but should be fine - for the actual
> reasoning
> >     behind it, see `Note [Disaster and iconv]` for more info.
> >
> >     In addition to this fix, we also patch up the IO Encoding utilities
> to
> >     recognize several variations of the 'ASCII' encoding (including its
> >     aliases) directly so that GHC can do conversions without iconv. This
> >     allows a static binary to sit in an initramfs.
> >
> >     Authored-by: Reid Barton <rwbarton at gmail.com>
> >     Authored-by: Sylvain Henry <hsyl20 at gmail.com>
> >     Signed-off-by: Austin Seipp <austin at well-typed.com>
> >
> >     Test Plan: Eyeballed it.
> >
> >     Reviewers: rwbarton, hvr
> >
> >     Subscribers: bgamari, thomie
> >
> >     Differential Revision: https://phabricator.haskell.org/D898
> >
> >     GHC Trac Issues: #10298, #7695
> >
> >     (cherry picked from commit e28462de700240288519a016d0fe44d4360d9ffd)
> >
> > >---------------------------------------------------------------
> >
> > 25b84781ed950d59c7bffb77a576d3c43a883ca9
> >  libraries/base/GHC/IO/Encoding.hs | 14 +++++++++++++-
> >  libraries/base/GHC/TopHandler.hs  | 29 ++++++++++++++++++++++++++++-
> >  2 files changed, 41 insertions(+), 2 deletions(-)
> >
> > diff --git a/libraries/base/GHC/IO/Encoding.hs
> b/libraries/base/GHC/IO/Encoding.hs
> > index 31683b4..014b61b 100644
> > --- a/libraries/base/GHC/IO/Encoding.hs
> > +++ b/libraries/base/GHC/IO/Encoding.hs
> > @@ -235,7 +235,14 @@ mkTextEncoding e = case mb_coding_failure_mode of
> >          _             -> Nothing
> >
> >  mkTextEncoding' :: CodingFailureMode -> String -> IO TextEncoding
> > -mkTextEncoding' cfm enc = case [toUpper c | c <- enc, c /= '-'] of
> > +mkTextEncoding' cfm enc
> > +  -- First, specifically match on ASCII encodings directly using
> > +  -- several possible aliases (specified by RFC 1345 & co), which
> > +  -- allows us to handle ASCII conversions without iconv at all (see
> > +  -- trac #10298).
> > +  | any (== enc) ansiEncNames = return (UTF8.mkUTF8 cfm)
> > +  -- Otherwise, handle other encoding needs via iconv.
> > +  | otherwise = case [toUpper c | c <- enc, c /= '-'] of
> >      "UTF8"    -> return $ UTF8.mkUTF8 cfm
> >      "UTF16"   -> return $ UTF16.mkUTF16 cfm
> >      "UTF16LE" -> return $ UTF16.mkUTF16le cfm
> > @@ -249,6 +256,11 @@ mkTextEncoding' cfm enc = case [toUpper c | c <-
> enc, c /= '-'] of
> >  #else
> >      _ -> Iconv.mkIconvEncoding cfm enc
> >  #endif
> > +  where
> > +    ansiEncNames = -- ASCII aliases
> > +      [ "ANSI_X3.4-1968", "iso-ir-6", "ANSI_X3.4-1986",
> "ISO_646.irv:1991"
> > +      , "US-ASCII", "us", "IBM367", "cp367", "csASCII", "ASCII",
> "ISO646-US"
> > +      ]
> >
> >  latin1_encode :: CharBuffer -> Buffer Word8 -> IO (CharBuffer, Buffer
> Word8)
> >  latin1_encode input output = fmap (\(_why,input',output') ->
> (input',output')) $ Latin1.latin1_encode input output -- unchecked, used
> for char8
> > diff --git a/libraries/base/GHC/TopHandler.hs
> b/libraries/base/GHC/TopHandler.hs
> > index d7c0038..e725196 100644
> > --- a/libraries/base/GHC/TopHandler.hs
> > +++ b/libraries/base/GHC/TopHandler.hs
> > @@ -157,13 +157,40 @@ real_handler exit se = do
> >             Just (ExitFailure n) -> exit n
> >
> >             -- EPIPE errors received for stdout are ignored (#2699)
> > -           _ -> case fromException se of
> > +           _ -> catch (case fromException se of
> >                  Just IOError{ ioe_type = ResourceVanished,
> >                                ioe_errno = Just ioe,
> >                                ioe_handle = Just hdl }
> >                     | Errno ioe == ePIPE, hdl == stdout -> exit 0
> >                  _ -> do reportError se
> >                          exit 1
> > +                ) (disasterHandler exit) -- See Note [Disaster with
> iconv]
> > +
> > +-- don't use errorBelch() directly, because we cannot call varargs
> functions
> > +-- using the FFI.
> > +foreign import ccall unsafe "HsBase.h errorBelch2"
> > +   errorBelch :: CString -> CString -> IO ()
> > +
> > +disasterHandler :: (Int -> IO a) -> IOError -> IO a
> > +disasterHandler exit _ =
> > +  withCAString "%s" $ \fmt ->
> > +    withCAString msgStr $ \msg ->
> > +      errorBelch fmt msg >> exit 1
> > +  where msgStr = "encountered an exception while trying to report an
> exception"
> > +
> > +{- Note [Disaster with iconv]
> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +When using iconv, it's possible for things like iconv_open to fail in
> > +restricted environments (like an initram or restricted container), but
> > +when this happens the error raised inevitably calls `peekCString`,
> > +which depends on the users locale, which depends on using
> > +`iconv_open`... which causes an infinite loop.
> > +
> > +This occurrence is also known as tickets #10298 and #7695. So to work
> > +around it we just set _another_ error handler and bail directly by
> > +calling the RTS, without iconv at all.
> > +-}
> >
> >
> >  -- try to flush stdout/stderr, but don't worry if we fail
> >
> --- End forwarded message ---
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