Bug 32094

The pkg-config man page says, when discussing an example .pc file:

"You would normally generate the file using configure, of course, so that the prefix, etc. are set to the proper values."

(e.g. as seen in http://cgit.freedesktop.org/pkg-config/tree/pkg-config.1)

I agree that this is normally what is done, but I don't think it is the best way to do it.  In particular, I think the best way to do it is at "make" time, not "configure" time.

For example, if you defer .pc generation until "make" time, you can generate .pc files based on a prefix which is based on a Makefile variable like $(abs_top_builddir).  For example, in configure.ac, you could do

AC_PREFIX_DEFAULT("\$(abs_top_builddir)/install")

If you (prematurely) generate the .pc file at "configure" time in such a situation, you'll get a broken .pc file because it will contain, literally, "$(abs_top_builddir)".  This is the most severe symptom of premature generation of the .pc file, and the one that brought the issue to my attention, but there is also just the general problem that, according to the GNU Coding Standards, you should be able to change the prefix at make time.

To me, the definitive reference here is the autoconf manual:

"[...] you should not rely on AC_CONFIG_FILES to replace bindir and friends in your shell scripts and other files; instead, let make manage their replacement."

I discussed the issue in detail in this post on the pkg-config discussion list:

http://lists.freedesktop.org/archives/pkg-config/2010-July/000645.html

I got no response there so I'm "escalating" the issue by logging this bug.