Re: conditional use of PKG_CHECK_MODULES, along with platforms that don't have pkg-config

[Pete Batard]

Hi Eric,

On 2010.09.21 19:06, Eric Blake wrote:
> Are you are trying to target development on these two machines (where
> both Linux and mingw users run autoreconf, and you don't want autoreconf
> to fail if PKG_CHECK_MODULES is used but pkg-config is not installed),
> or are you targeting the end-user (where as long as the code for
> PKG_CHECK_MODULES is never reached, it shouldn't matter if the end user
> doesn't have pkg-config installed)?

I guess that would be development on the 2 machines. If you want some 
background, this configure.ac [1] is to be used in the libusb project 
[2], where we are in the process of adding hotplug support for Linux, 
Mac and Windows. On Linux platforms, hotplug comes from libudev, so we 
thought we'd use PKG_CHECK_MODULES to sort everything out with little 
effort, whereas on Mac and Windows, no additional libraries are needed 
and we typically expect users not to have pkg-config installed.

> Insufficient m4 quoting. Get in the habit of using proper quotation, so
> you can avoid subtle bugs later:

Good point. Will fix that.

> Can
> you instead write your tests using AC_SEARCH_LIBS, to see if libudev is
> available (whether or not you are on Linux or mingw)?

Yes, that's the fallback option. We have some developers on our end who 
are very positive about pkg-config simplifying the dependency issue, so 
it seemed like a sensible approach on Linux.

> Not being entirely familiar with the guts of PKG_CHECK_MODULES, what
> exactly is it doing wrong on mingw that you are trying to avoid?

Well, on MinGW, because pkg-config is not supposed to be available, and 
we don't require additional libraries for hotplug, there is little point 
of using PKG_CHECK_MODULES.

> If your problem is only one at autoreconf (that is, you are targeting
> mingw development), you are free to ship additional m4 files in your
> tarball, including the pkg-config.m4 file from pkg-config. True, that
> means that you are introducing a potential version skew issue if your
> package bundled an older version of that file than what would be on the
> developer's machine when pkg-config is installed, but it means that the
> macro is always available for developers.

That's an idea. We'll look into that.

Regards,

/Pete

[1] http://git.libusb.org/?p=libusb-pbatard.git;a=blob;f=configure.ac
[2] http://libusb.org/