cpphs: can't be used to build GHC 7.10.3. Bug?

[Alain O'Dea]

No worries. Thank you Malcolm. If there's anything else I can gather to
facilitate the fix let me know.
On Sun, Jan 10, 2016 at 5:40 PM Malcolm Wallace <malcolm.wallace at me.com>
wrote:

> Thanks for the bug report, and for the detailed analysis.  I will try to
> look at and fix this soon.
>
> Regards,
>     Malcolm
>
> On 10 Jan 2016, at 20:09, Alain O'Dea wrote:
>
> > Got a clear answer about the handling of if defined.
> >
> > Expanding macros within if defined is non-compliant if cpphs is trying
> to be a C99 preprocessor:
> > http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
> > 6.10.1/1 Conditional Inclusion pg 148 indicates that the token after
> defined or within defined ( ) is an identifier, not a macro to be expanded.
> >
> > I'm not sure what's involved in fixing this behavior in cpphs, but I'm
> happy to test fixes.
> >
> > On Sun, Jan 10, 2016 at 3:53 PM Alain O'Dea <alain.odea at gmail.com>
> wrote:
> > I've isolated the issue to the handling of if defined on multi-argument
> macros.
> >
> > I took a crack at interpreting the cpphs source for this and I think it
> may be a bug in the conversion of defined expressions here in
> Language.Preprocessor.CppIfdef here:
> >
> >     convert "defined" [arg] =
> >       case lookupST arg st of
> >         Nothing | all isDigit arg    -> return arg
> >         Nothing                      -> return "0"
> >         Just (a at AntiDefined{})       -> return "0"
> >         Just (a at SymbolReplacement{}) -> return "1"
> >         Just (a at MacroExpansion{})    -> return "1"
> >
> > It looks like it will macro expand the contents of a defined expression
> which isn't what GCC does.  I don't know if GCC is wrong or if using
> parameterized macros within
> >
> > if defined works on single-argument macros.
> >
> > working1.hs:
> >
> >     {-# LANGUAGE CPP #-}
> >
> >     #define EXAMPLE_MACRO(arg) (\
> >                                    arg)
> >
> >     #if defined(EXAMPLE_MACRO)
> >     #endif
> >
> > preprocess it (it works!):
> >
> >     $ cpphs --cpp working1.hs -o $tempfile
> >     $
> >
> > ifdef works on multiple-argument macros.
> >
> > working2.hs:
> >
> >     {-# LANGUAGE CPP #-}
> >
> >     #define EXAMPLE_MACRO(arg1,arg2) (\
> >                                    arg1 > arg2)
> >
> >     #ifdef EXAMPLE_MACRO
> >     #endif
> >
> > preprocess it (it works!):
> >
> >     $ cpphs --cpp working2.hs -o $tempfile
> >     $
> >
> > if defined fails on multi-argument macros.
> >
> > broken2.hs:
> >
> >     {-# LANGUAGE CPP #-}
> >
> >     #define EXAMPLE_MACRO(arg1,arg2) (\
> >                                    arg1 > arg2)
> >
> >     #if defined(EXAMPLE_MACRO)
> >     #endif
> >
> > preprocess it (it fails!):
> >
> >     $ cpphs --cpp broken2.hs -o $tempfile
> >     cpphs: macro EXAMPLE_MACRO expected 2 arguments, but was given 0
> >     $
> >
> > I've posted a StackOverflow question to see if any of them know if this
> is undefined behavior:
> >
> http://stackoverflow.com/questions/34709769/is-cpphs-wrong-or-is-the-behavior-of-macros-with-arguments-in-if-defined-express
> >
> > If it is undefined behavior we should stop relying on it in GHC
> sources.  Either way the behavior is inconsistent with GCC which
> complicates things.
> >
> > Best,
> > Alain
> >
> > On Sun, Jan 10, 2016 at 2:04 PM Alain O'Dea <alain.odea at gmail.com>
> wrote:
> > Hi Malcolm:
> >
> > cpphs is under consideration as a replacement for GCC's C preprocessor
> in the GHC toolchain:
> > https://ghc.haskell.org/trac/ghc/wiki/Proposal/NativeCpp
> >
> > GHC 7.10.3's build fails when cpphs is used as the C preprocessor
> (--with-hs-cpp=cpphs --with-hs-cpp-flags="--cpp").
> >
> > It runs into this error when preprocessing libraries/base/GHC/Natural.hs:
> >
> > cpphs: macro MIN_VERSION_integer_gmp expected 3 arguments, but was given
> 0
> >
> > I've reproduced this issue on Ubuntu 14.04 x86-64 and SmartOS 15.3.0
> x86-64.
> >
> > Interestingly the error seems to arise only when preprocessing
> Natural.hs while the autogenerated cabal-macros.h is present.  Removing
> that include from the cpphs flags leads to a clean preprocessing run.
> >
> > I have more details of this investigation here:
> > https://gist.github.com/AlainODea/bd5b3e0e6f7c4227f009
> >
> > Is this a bug?
> >
> > Best,
> > Alain
>
>
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