[PATCH input-synaptics 1/5] Use appropriate Autoconf statements to check for prerequisites

[Dan Nicholson]

On Tue, Jun 14, 2011 at 6:45 AM, Gaetan Nadon <memsize at videotron.ca> wrote:
> On Tue, 2011-06-14 at 10:56 +0200, Diego Elio Pettenò wrote:
>
> Il giorno lun, 13/06/2011 alle 19.43 -0400, Gaetan Nadon ha scritto:
>>
>> Using m4 to check for macro defined by the xserver to ensure it is
>> installed
>> will work as long as the macro is not removed. The preferred way of
>> checking
>> for dependencies is to use PKG_CHECK_MODULE.
>
> Different moment to check for them:
>
> - PKG_CHECK_MODULE check presence when running ./configure
> - m4_ifndef when autoconf is executed.
>
> If you build autotools for the package on a system that has no
> xorg-server installed, you'll receive a broken configure script, thus
> why I wanted to make it explicit that you need to have it around at
> autoconf time.
>
> What is the benefit of having:
>
> autoreconf: running: aclocal -I /home/nadon/xorg/src/inst/share/aclocal
> --force
> configure.ac:51: error: must install xorg-server development files before
> running autoconf/autogen
>
> over having:
>
> checking for XORG... no
> configure: error: Package requirements (xorg-server >= 1.6) were not met:
>
> Dan is also of the opinion that it is preferable, but I just can't see why.
> In a distro building world perhaps?

It's simple: XORG_DRIVER_CHECK_EXT is required at autoconf time
whereas PKG_CHECK_MODULES doesn't operate until build time. You could
generate a broken configure script if the macro isn't available. IMO,
it's just good practice to catch errors at the appropriate time. I
don't see a drawback to checking whether an external macro is
available when it needs to be used.

> One drawback is the m4 test "fails to fail" when the server is uninstalled
> after synaptics have been configured as the XORG macro is cached. The
> following PKG_CHECK_MODULE will stop on error, however. Maybe this is the
> way it should work.

How would it "fail to fail"? If xorg-server.h isn't installed anymore,
then you won't get the extension. The macro is intended to check if an
extension is available in the server, and it does just that. I guess
you want it to fail harder if the xserver can't be found at all.

--
Dan