Emit correct pkg-config file if paths are absolute

[marcin-serwin]

CMAKE_INSTALL_INCLUDEDIR and CMAKE_INSTALL_LIBDIR may be defined to be absolute paths. In this situation they should not be appended to the prefix.

[sammycage]

@dg0yt

[marcin-serwin]

@dg0yt bump

[dg0yt]

FTR CMake now even stronger recommends to not use absolute paths:

"While absolute paths are allowed, they are not recommended as they do not work with the cmake --install command's --prefix option, or with the cpack installer generators."

https://cmake.org/cmake/help/v4.1/module/GNUInstallDirs.html

Does this package really need the extra complexity for supporting a case which is not recommended?

[marcin-serwin]

Absolute paths are used extensively by nixpkgs for installing development files into a separate prefix -- ignoring --prefix is precisely what we want in such cases so the warning is not relevant.

The complexity could be lowered a bit by bumping minimum cmake to 3.20 -- it introduces cmake_path command that could be used for path construction.

[dg0yt]

get_filename_component should be good enough. If you are so familiar with CMake and your requirement, why not make a PR?

[marcin-serwin]

get_filename_component should be good enough.

From its docs:

Changed in version 3.20: This command has been superseded by the cmake_path() command

so not sure if it's worth doing.

If you are so familiar with CMake and your requirement, why not make a PR?

What do you mean? We are literally reviewing my PR...

[dg0yt]

In fact I didn't review so far...

[marcin-serwin]

After reading the docs I don't see how get_filename_component could be used to achieve this, it doesn't have the equivalent of APPEND from cmake_path.

[dg0yt]

Well, I didn't ask for ping, bump or cmake_path. AFAICT path construction with / is robust enough here.

[marcin-serwin]

Thanks for the review. Sorry for bumping you, I was just following what @sammycage did.