bug#23034: AC_CHECK_HEADERS after GUILE_FLAGS loses $CPP

bug#23034: AC_CHECK_HEADERS after GUILE_FLAGS loses $CPP

[Bernd Jendrissek]

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I have a reduced test case where adding GUILE_FLAGS in shell dead code
before a call to AC_CHECK_HEADERS causes configure to lose $CPP, which
results in warnings like this one:

checking stdarg.h usability... yes
checking stdarg.h presence... no
configure: WARNING: stdarg.h: accepted by the compiler, rejected by
the preprocessor!
configure: WARNING: stdarg.h: proceeding with the compiler's result
checking for stdarg.h... yes

Versions:

/usr/share/aclocal/guile.m4: guile-2.0-dev from Debian jessie (2.0.11+1-9)
autoconf: 2.69

Attached:

configure.ac
guile.m4

To reproduce:

Find a config.rpath somewhere (perhaps steal it from gettext).
autoreconf -fi
./configure

I noticed that a random recent git HEAD of autoconf avoids this
problem; it turns out that in commit
11f520c61d8b21f1522968d6e6afb899070f0a6f autoconf transitions to
compilation-only header checks.

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AC_INIT([guileflags], [1.5.0], [foo@example.com])
AC_PREREQ(2.54)

# Checks for programs.
AC_PROG_CC

if false
then
   GUILE_FLAGS
fi
AC_CHECK_HEADERS([stdarg.h])
echo "ac_cpp=$ac_cpp CPP=$CPP" >&6

AC_OUTPUT

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bug#23034: AC_CHECK_HEADERS after GUILE_FLAGS loses $CPP

[Andy Wingo]

On Thu 17 Mar 2016 02:47, Bernd Jendrissek <bernd@bpj-code.co.za> writes:

> I have a reduced test case where adding GUILE_FLAGS in shell dead code
> before a call to AC_CHECK_HEADERS causes configure to lose $CPP, which
> results in warnings like this one:
>
> checking stdarg.h usability... yes
> checking stdarg.h presence... no
> configure: WARNING: stdarg.h: accepted by the compiler, rejected by
> the preprocessor!
> configure: WARNING: stdarg.h: proceeding with the compiler's result
> checking for stdarg.h... yes
>
> Versions:
>
> /usr/share/aclocal/guile.m4: guile-2.0-dev from Debian jessie (2.0.11+1-9)
> autoconf: 2.69
>
> Attached:
>
> configure.ac
> guile.m4
>
> To reproduce:
>
> Find a config.rpath somewhere (perhaps steal it from gettext).
> autoreconf -fi
> ./configure
>
> I noticed that a random recent git HEAD of autoconf avoids this
> problem; it turns out that in commit
> 11f520c61d8b21f1522968d6e6afb899070f0a6f autoconf transitions to
> compilation-only header checks.

AFAIU then this is an autoconf bug?  Weird.  Weird also that autoconf is
just not releasing these days!  I guess we close this from the Guile
point of view though, no?

Regarding autoconf releases:

  http://lists.gnu.org/archive/html/autoconf/2016-12/msg00005.html

So, I will optimistically close this and this problem will go away once
autoconf 2.70 is out.

Andy