Short summary of my use case:

• in MSYS2 we want/need to update to ffmpeg 5 while keeping 4.4 for some packages
• for this we install the .pc files into <prefix>/lib/ffmpeg4.4/pkgconfig/ instead of <prefix>/lib/pkgconfig/ (we just set a different --incdir and --libdir to ffmpeg configure) so we can set the alternative pc path via something like export PKG_CONFIG_PATH="${MINGW_PREFIX}/lib/ffmpeg4.4/pkgconfig:$PKG_CONFIG_PATH" when wanting a package to links against 4.4

Problem:

The define-prefix logic in pkgconf doesn't support this since it just strips "/pkgconfig" from paths, so the detected prefix is

• "<prefix>/lib/ffmpeg4.4/pkgconfig" instead of
• "<prefix>/lib/ffmpeg4.4/pkgconfig".

So we get the following wrong output (one "/lib" too much):

$ export PKG_CONFIG_PATH="${MINGW_PREFIX}/lib/ffmpeg4.4/pkgconfig:$PKG_CONFIG_PATH"
$ pkgconf.exe --libs --cflags libavcodec
-IC:/msys64/ucrt64/lib/include/ffmpeg4.4 -LC:/msys64/ucrt64/lib/lib/ffmpeg4.4 -lavcodec

Context / Question:

The logic for this is defined here:

• pkgconf:

  pkgconf/libpkgconf/pkg.c

  Line 204 in 78f3abc

  determine_prefix(const pkgconf_pkg_t *pkg, char *buf, size_t buflen)

• The same logic in pkg-config: https://gitlab.freedesktop.org/pkg-config/pkg-config/-/blob/d97db4fae4c1cd099b506970b285dc2afd818ea2/parse.c#L1000

I'm not quite sure how to work around/fix that without hacks, so I'm asking here if someone had a similar problem and maybe an idea for a solution or a workaround.

The only thing I can think of is patching the .pc files after the build from libdir=${prefix}/lib/ffmpeg4.4 to libdir=${prefix}/../lib/ffmpeg4.4

If there is no solution feel free to close. At least I can link to this issue from my workarounds :)