pkgconf/README.md

# pkgconf

`pkgconf` is a program which helps to configure compiler and linker flags for
development libraries.  It is similar to pkg-config from freedesktop.org.

`libpkgconf` is a library which provides access to most of `pkgconf`'s functionality, to allow
other tooling such as compilers and IDEs to discover and use libraries configured by
pkgconf.

## using `pkgconf` with autotools

Implementations of pkg-config, such as pkgconf, are typically used with the
PKG_CHECK_MODULES autoconf macro.  As far as we know, pkgconf is
compatible with all known variations of this macro. pkgconf detects at
runtime whether or not it was started as 'pkg-config', and if so, attempts
to set program options such that its behaviour is similar.

In terms of the autoconf macro, it is possible to specify the PKG_CONFIG
environment variable, so that you can test pkgconf without overwriting your
pkg-config binary.  Some other build systems may also respect the PKG_CONFIG
environment variable.

To set the environment variable on the bourne shell and clones (i.e. bash), you
can run:

    $ export PKG_CONFIG=/usr/bin/pkgconf

## comparison of `pkgconf` and `pkg-config` dependency resolvers

pkgconf builds an acyclic directed dependency graph.  This allows for the user
to more conservatively link their binaries -- which may be helpful in some
environments, such as when prelink(1) is being used.  As a result of building
a directed dependency graph designed for the specific problem domain provided
by the user, more accurate dependencies can be determined.

Current release versions of pkg-config, on the other hand, build a database of all
known pkg-config files on the system before attempting to resolve dependencies, which
is a considerably slower and less efficient design.  Efforts have been made recently
to improve this behaviour.

As of the 1.1 series, pkgconf also fully implements support for `Provides` rules,
while pkg-config does not.  pkg-config only provides the `--print-provides` functionality
as a stub.  There are other intentional implementation differences in pkgconf's dependency
resolver verses pkg-config's dependency resolver in terms of completeness and correctness,
such as, for example, how `Conflicts` rules are processed.

## linker flags optimization

As previously mentioned, pkgconf makes optimizations to the linker flags in both the
case of static and shared linking in order to avoid overlinking binaries and also
simplifies the `CFLAGS` and `LIBS` output of the pkgconf tool for improved readability.

This functionality depends on the pkg-config module properly declaring it's dependency
tree instead of using `Libs` and `Cflags` fields to directly link against other modules
which have pkg-config metadata files installed.

Doing so is discouraged by the [freedesktop tutorial][fd-tut] anyway.

   [fd-tut]: http://people.freedesktop.org/~dbn/pkg-config-guide.html

## compatibility with pkg-config

We do not provide bug-level compatibility with pkg-config.

What that means is, if you feel that there is a legitimate regression versus pkg-config,
do let us know, but also make sure that the .pc files are valid and follow the rules of
the [pkg-config tutorial][fd-tut], as most likely fixing them to follow the specified
rules will solve the problem.

## compiling `pkgconf` and `libpkgconf` on UNIX

pkgconf is basically compiled the same way any other autotools-based project is
compiled:

    $ ./configure
    $ make
    $ sudo make install

If you are installing pkgconf into a custom prefix, such as `/opt/pkgconf`, you will
likely want to define the default system includedir and libdir for your toolchain.
To do this, use the `--with-system-includedir` and `--with-system-libdir` configure
flags like so:

    $ ./configure \
         --prefix=/opt/pkgconf \
         --with-system-libdir=/lib:/usr/lib \
         --with-system-includedir=/usr/include
    $ make
    $ sudo make install

## compiling `pkgconf` and `libpkgconf` with CMake (usually for Windows)

pkgconf is compiled using CMake on Windows.  In theory, you could also use CMake to build
on UNIX, but this is not recommended at this time as it pkgconf is typically built much earlier
than CMake.

    $ mkdir build
    $ cd build
    $ cmake ..
    $ make
    $ sudo make install

There are a few defines such as SYSTEM_LIBDIR, PKGCONFIGDIR and SYSTEM_INCLUDEDIR.
However, on Windows, the default PKGCONFIGDIR value is usually overridden at runtime based
on path relocation.

## pkg-config symlink

If you want pkgconf to be used when you invoke `pkg-config`, you should install a
symlink for this.  We do not do this for you, as we believe it is better for vendors
to make this determination themselves.

    $ ln -sf pkgconf /usr/bin/pkg-config

## release tarballs

Release tarballs are available at <https://distfiles.dereferenced.org/pkgconf/>.
Please only use the tarballs from distfiles.dereferenced.org.

## reporting bugs

See <https://git.dereferenced.org/pkgconf/pkgconf/issues>.

Also you can contact us at `#pkgconf` at `irc.freenode.net`.