Re: [sr #110271] libSDL2 fails with autoconf 2.70

On 2020-07-16, Ross Burton <[email protected]> wrote:
[...]]
> libSDL2 fails to configure with autoconf 2.70 but works with 2.69:
>
> | checking for size_t... yes
> | checking for M_PI in math.h... ../SDL2-2.0.12/configure: line 13202: CPP:
> command not found
> | checking how to run the C preprocessor... gcc  -E
> | ../SDL2-2.0.12/configure: line 13328: ac_fn_c_try_cpp: command not found
> | ../SDL2-2.0.12/configure: line 13328: ac_fn_c_try_cpp: command not found
> | configure: error: in
> `/home/pokybuild/yocto-worker/qemux86-64/build/build/tmp/work/x86_64-linux/libsdl2-native/2.0.12-r0/build':
> | configure: error: C preprocessor "gcc  -E" fails sanity check
> | See `config.log' for more details
> | WARNING: exit code 1 from a shell command.
>
> The configure.ac is just a very badly named macro:
>
>     AC_CHECK_DEFINE(M_PI, math.h)
>
> Which is implemented here:
>
> https://github.com/spurious/SDL-mirror/blob/master/acinclude/ac_check_define.m4
>
> This uses AC_EGREP_CPP but it doesn't appear to explicitly look for a cpp.
> My workaround is to explicltly call AC_PROG_CPP earlier: should AC_EGREP_CPP
> be doing this, or should this requirement be documented?

This is a classic M4 quoting bug.  The macro should quote the third
argument to AC_CACHE_CHECK (and really, should quote all the arguments).

The problem is that diversions do not work properly during arugment
collection so AC_REQUIRE (which depends on diversions) and many other
macros will not work properly if it is expanded during argument
collection.

Quote the arguments to AC_CACHE_CHECK and the prerequisite macros will
get expanded in the correct order.

(also WTF is with that stray AC_DEFINE outside of the macro definition?)

Cheers,
  Nick