[cairo] Build failures with cached configure results

[Uli Schlachter]

Hi,

the current configure.ac often causes build failures when configure is re-run
with a cache. For example, I just had this build failure:

  CC     cairo-xlib-display.lo
In file included from cairo-xlib-private.h:42,
                 from cairo-xlib-display.c:39:
cairo-xlib-xrender-private.h:102: error: redefinition of ‘struct _XLinearGradient’
cairo-xlib-xrender-private.h:105: error: conflicting types for ‘XLinearGradient’
/usr/include/X11/extensions/Xrender.h:189: note: previous declaration of
‘XLinearGradient’ was here
[...]
(This can be triggered with 'touch configure.ac && make')

The reason for this is that all the different CAIRO_ENABLE_* macros are used
incorrectly. These macros map to _CAIRO_ENABLE in build/aclocal.enable.m4 which
runs the specified test command via AC_CACHE_CHECK. AC_CACHE_CHECK's
documentation contains this[1]:

   The commands-to-set-it must have no side effects except for setting
   the variable cache-id, see below.

The reason for the build "redefinition of struct _XLinearGradient" that I
mentioned above is that the CAIRO_ENABLE_SURFACE_BACKEND for xlib_xrender uses
AC_CHECK_FUNCS in it's "COMMANDS" for checking. So if the result for
xlib_xrender is taken from the cache, the AC_CHECK_FUNCS for
XRenderCreate*Gradient is not executed.

The problem here is that basically no code in configure.ac gets this right and
thus it would be a huge task to fix this.


Attached is a patch which disables the cache for _CAIRO_ENABLE. This is a bad
idea to do, but works for me(tm).

Any suggestions what can be done about this? Who's the local autoconf expert who
feels obligated to fix this? ;-)

Cheers,
Uli

[1]
http://www.gnu.org/software/autoconf/manual/html_node/Caching-Results.html#index-AC_005fCACHE_005fCHECK-1154
-- 
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