Question: correct way to use Requires.private

[freeekanayaka]

Hi,

I'm trying to understand how to correctly use the Requires.private property in a .pc file.

Let's say that libA internally depends on libB and that libA.so is dynamically linked to libB.so when libA is built as shared library.

My understanding is that libA should include libB in its Requires.private .pc file, is that right?

That would be mainly in order to support static builds.

Now, let's say that my-app is using libA and uses PKG_CHECK_MODULES in its configure.ac to detect the presence of libA. As far as I can see if Requires.private is used, the configure script of my-app will fail with something:

configure: error: Package requirements (libA >= 0.0.1) were not met:

Package 'libB', required by 'libA', not found

if the .pc file of libB is not installed on the system. This happens because the pkg.m4 macros generates a command like:

/usr/bin/pkg-config --cflags "libA >= 0.0.1"

which fails with:

Package libB was not found in the pkg-config search path.
Perhaps you should add the directory containing `libB.pc'
to the PKG_CONFIG_PATH environment variable
Package 'libB', required by 'libA', not found

Distributions like Debian ship .pc files in a separate -dev package, so the scenario in which the .pc file of libA is present, but the one of libB is not is actually the normal one, because a user building my-app should only need the the libA-dev package.

Should perhaps Libs.private be used instead? I'm confused about the proper way to do this.

Thanks

[kaniini]

Requires.private is always considered for CFLAGS, because the module's headers may be referenced by the dependent (in fact, this would make a lot of sense, consider a module which builds on top of GTK, for example, it would need to reference the GTK headers).

Requires.private is only considered for LIBS if --static is also requested.

[freeekanayaka]

Requires.private is always considered for CFLAGS, because the module's headers may be referenced by the dependent (in fact, this would make a lot of sense, consider a module which builds on top of GTK, for example, it would need to reference the GTK headers).

Requires.private is only considered for LIBS if --static is also requested.

Thanks for your reply, I had missed it and I'm only reading it now. What if the modules headers are not referenced by the dependent? Is there a way to have CFLAGS behave in the same way as LIBS? I.e. make Requires.private only considered if --static is requested, both for LIBS and CFLAGS.

[floppym]

See also https://gitlab.freedesktop.org/pkg-config/pkg-config/-/issues/7.

[kaniini]

Documentation clarifying the current situation was merged in #353.