[Agda-dev] Unnecessary warning from cpphs on GHC 7.10.1 RC1

[Andrés Sicard-Ramírez]

Hi Malcolm,

While preparing Agda for supporting GHC 7.10.1, I found the following issue
on cpphs.

For example, using the file
https://github.com/simonmar/alex/blob/3.1.4/tests/tokens.x, Alex includes
the file ghcconfig.h which generates the following warning:

  $ ghc --version
  The Glorious Glasgow Haskell Compilation System, version 7.10.0.20141222

  $ alex --version
  Alex version 3.1.4, (c) 2003 Chris Dornan and Simon Marlow

​  ​$ alex Tokens.x

  $ ghc -pgmP cpphs -optP --cpp Tokens.hs
  Warning: Can't find file
"/usr/local/stow/ghc-7.10.0.20141222-bin/lib/ghc-7.10.0.20141222/include/ghcversion.h"
in   directories
    .

/usr/local/stow/ghc-7.10.0.20141222-bin/lib/ghc-7.10.0.20141222/base_469rOtLAqwTGFEOGWxSUiQ/include

/usr/local/stow/ghc-7.10.0.20141222-bin/lib/ghc-7.10.0.20141222/integ_21cuTlnn00eFNd4GMrxOMi/include
    /usr/local/stow/ghc-7.10.0.20141222-bin/lib/ghc-7.10.0.20141222/include
  Asked for by: Tokens.hs  at line 1 col 1

I think the above warning is unnecessary because cpphs found the file in a
different directory.

Notes:

1. The unnecessary warning doesn't show up when using GHC 7.8.4.

2. Note that cpphs (but not cpp) correctly generates the warning

  Warning: trailing characters after #if directive in file
/usr/local/stow/ghc-7.10.0.20141222-bin/lib/ghc-7.10.0.20141222/include/ghcautoconf.h
 at line 379 col 1:  AC_APPLE_UNIVERSAL_BUILD

(I reported this warning in https://ghc.haskell.org/trac/ghc/ticket/9213).

Best,

-- 
Andrés
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