*

A checklist for writing pkg-config files

Philip Withnall avatar

Posted on 09/12/2014 by Philip Withnall

Share this post:

tl;dr: Use AX_PKG_CHECK_MODULES to split public/private dependencies; use AC_CONFIG_FILES to magically include the API version in the .pc file name.

A few tips for creating a pkg-config file which you will never need to think about maintaining again — because one of the most common problems with pkg-config files is that their dependency lists are years out of date compared to the dependencies checked for inconfigure.ac. See lower down for some example automake snippets.

  • Include the project’s major API version1 in the pkg-config file name. e.g. libfoo-1.pcrather than libfoo.pc. This will allow parallel installation of two API-incompatible versions of the library if it becomes necessary in future.
  • Split private and public dependencies between Requires and Requires.private. Thiseliminates over-linking when dynamically linking against the project, since in that case the private dependencies are not needed. This is easily done using theAX_PKG_CHECK_MODULES macro (and perhaps using an upstream macro in future — seepkg-config bug #87154). A dependency is public when its symbols are exposed in public headers installed by your project; it is private otherwise.
  • Include useful ancillary variables, such as the paths to any utilities, directories or daemons which ship with the project. For example, glib-2.0.pc has variables giving the paths for its utilities: glib-genmarshalgobject-query and glib-mkenumslibosinfo-1.0.pchas variables for its database directories.
  • Substitute in the Name and Version using @PACKAGE_NAME@ and @PACKAGE_VERSION@ so they don’t fall out of sync.
  • Place the .pc.in template in the source code subdirectory for the library it’s for — so if your project produces multiple libraries (or might do in future), the .pc.in files don’t get mixed up at the top level.

Given all those suggestions, here’s a template libmy-project/my-project.pc.in file:

prefix=@prefix@
exec_prefix=@exec_prefix@
libdir=@libdir@
includedir=@includedir@
 
my_project_utility=my-project-utility-binary-name
my_project_db_dir=@sysconfdir@/my-project/db
 
Name: @PACKAGE_NAME@
Description: Some brief but informative description
Version: @PACKAGE_VERSION@
Libs: -L${libdir} -lmy-project-@API_VERSION@
Cflags: -I${includedir}/my-project-@API_VERSION@
Requires: @AX_PACKAGE_REQUIRES@
Requires.private: @AX_PACKAGE_REQUIRES_PRIVATE@

 

And here’s a a few snippets from a template configure.ac:

# Release version
m4_define([package_version_major],[1])
m4_define([package_version_minor],[2])
m4_define([package_version_micro],[3])
 
# API version
m4_define([api_version],[1])
 
AC_INIT([my-project],
        [package_version_major.package_version_minor.package_version_micro],
        …)
 
# Dependencies
PKG_PROG_PKG_CONFIG
 
glib_reqs=2.40
gio_reqs=2.42
gthread_reqs=2.40
nice_reqs=0.1.6
 
# The first list on each line is public; the second is private.
# The AX_PKG_CHECK_MODULES macro substitutes AX_PACKAGE_REQUIRES and
# AX_PACKAGE_REQUIRES_PRIVATE.
AX_PKG_CHECK_MODULES([GLIB],
                     [glib-2.0 >= $glib_reqs gio-2.0 >= $gio_reqs],
                     [gthread-2.0 >= $gthread_reqs])
AX_PKG_CHECK_MODULES([NICE],
                     [nice >= $nice_reqs],
                     [])
 
AC_SUBST([PACKAGE_VERSION_MAJOR],package_version_major)
AC_SUBST([PACKAGE_VERSION_MINOR],package_version_minor)
AC_SUBST([PACKAGE_VERSION_MICRO],package_version_micro)
AC_SUBST([API_VERSION],api_version)
 
# Output files
# Rename the template .pc file to include the API version on configure
AC_CONFIG_FILES([
libmy-project/my-project-$API_VERSION.pc:libmy-project/my-project.pc.in
…
],[],
[API_VERSION='$API_VERSION'])
AC_OUTPUT

And finally, the top-level Makefile.am:

# Install the pkg-config file.
pkgconfigdir = $(libdir)/pkgconfig
pkgconfig_DATA = libmy-project/my-project-$(API_VERSION).pc
 
DISTCLEANFILES += $(pkgconfig_DATA)
EXTRA_DIST += libmy-project/my-project.pc.in

Once that’s all built, you’ll end up with an installed my-project-1.pc file containing the following (assuming a prefix of /usr):

prefix=/usr
exec_prefix=/usr
libdir=/usr/lib
includedir=/usr/include
 
my_project_utility=my-project-utility-binary-name
my_project_db_dir=/etc/my-project/db
 
Name: my-project
Description: Some brief but informative description
Version: 1.2.3
Libs: -L${libdir} -lmy-project-1
Cflags: -I${includedir}/my-project-1
Requires: glib-2.0 >= 2.40 gio-2.0 >= 2.42 nice >= 0.1.6
Requires.private: gthread-2.0 >= 2.40

All code samples in this post are released into the public domain.


  1. Assuming this is the number which will change if backwards-incompatible API/ABI changes are made.

    Original post

Related Posts

Related Posts

Comments (0)


Add a Comment






Allowed tags: <b><i><br>Add a new comment:


Latest Blog Posts

Quick hack: Speed up your GitLab CI

06/11/2018

Did you know you could register your own PC, or a spare laptop collecting dust in a drawer, to get instant CI going on GitLab? Not only…

Introducing Zink, an OpenGL implementation on top of Vulkan

31/10/2018

For the last month or so, I've been playing with a new project during my work at Collabora, and as I've already briefly talked about at…

On the low adoption of automated testing in FOSS

18/10/2018

For projects of any value and significance, having a comprehensive automated test suite is nowadays considered a standard software engineering…

Recently in Geoclue

12/10/2018

After I started working for Collabora in April, I've finally been able to put some time on maintenance and development of Geoclue again.…

The beauty of Open Source

10/10/2018

Like all software, Open Source software isn't without it's bugs and issues. However, thanks to the nature of Open Source, resolving or mitigating…

MicroDebConf Brasilia

02/10/2018

Last month, the first "MicroDebConf" took place at the Gama campus of the University of Brasilia. Here's a look at how this one day event…

Open Since 2005 logo

We use cookies on this website to ensure that you get the best experience. By continuing to use this website you are consenting to the use of these cookies. To find out more please follow this link.

Collabora Ltd © 2005-2018. All rights reserved. Website sitemap.