Use GNUInstallDirs module for cmake install paths

[JonnyPtn]

• Has this change been discussed on the forum or in an issue before?
• Does the code follow the SFML Code Style Guide?
• Have you provided some example/test code for your changes?
• If you have additional steps which need to be performed list them as tasks!

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Description

This replaces our custom install paths with the ones from the cmake GnuInstallDirs module

This PR is related to the issue #1563

Tasks

• Tested on Linux
• Tested on Windows
• Tested on macOS
• Tested on iOS
• Tested on Android

How to test this PR?

Build and install SFML (preferably to a custom CMAKE_INSTALL_PREFIX) and check the directory structure.

Seems I'm not able to request reviewers, but @eliasdaler , @fxcoudert and @Ceylo would be great to take a look

[eXpl0it3r]

Beyond the example directory thingy, this looks good. Tested it on Windows 10 and Debian 9.

[eXpl0it3r]

@jcowgill can you give feedback on this, especially w.r.t. pkgconfig?

[jcowgill]

Presumably this section of Macros.cmake needs updating?

    # add the install rule
    install(TARGETS ${target} EXPORT SFMLConfigExport
            RUNTIME DESTINATION bin COMPONENT bin
            LIBRARY DESTINATION lib${LIB_SUFFIX} COMPONENT bin
            ARCHIVE DESTINATION lib${LIB_SUFFIX} COMPONENT devel
            FRAMEWORK DESTINATION "." COMPONENT bin)

[jcowgill]

And I expect to do this properly, all occurrences of lib${LIB_SUFFIX} should be replaced with ${CMAKE_INSTALL_LIBDIR}

[jcowgill]

And for pkg-config specifically, ${CMAKE_INSTALL_LIBDIR}/pkgconfig is the correct directory to use by default (but keep the extra override for BSD systems).

[JonnyPtn]

Thanks for the feedback @jcowgill, think I've covered them all now?

[eliasdaler]

Overall, it looks good. I'll test on Linux soon.

I feel like we need to summarize somewhere which variables from GNUInstallDirs are used, because previously we had variables which were visible at configuration step, but now users might not know which variables control where stuff gets installed.

[JonnyPtn]

Not sure how much benefit there is to us explaining these variables, and it's kind of out of SFML scope. Realistically the user should only need to worry about CMAKE_INSTALL_PREFIX, and anything else is more advanced usage which they can probably work out on their own.

I think if we add a comment linking to the cmake docs this should suffice, but I'm happy to add more if that's the decision

[eliasdaler]

Realistically the user should only need to worry about CMAKE_INSTALL_PREFIX, and anything else is more advanced usage which they can probably work out on their own.

Yeah, agreed. Okay, it's good enough for now. 👍

[JonnyPtn]

Have just noticed this will break the xcode templates which rely on SFML_DEPENDENCIES_INSTALL_PREFIX to copy the frameworks into the app bundle...

I can probably change it to use the generator expression for the output directory of SFML if that's suitable?

[eXpl0it3r]

Sounds good to me, even though I don't fully understand the implications.

Looks like the Android build fails, do we have to adjust builbot as well?

[jcowgill]

There are still a few instances of LIB_SUFFIX left in the pkg-config files in tools/pkg-config/. It's also set once in the Android code in CMakeLists.txt, but I'm not sure what to do about that though.

[JonnyPtn]

I think that's the pkg config stuff sorted @jcowgill?

For the xcode template, even after updating the paths in the post build step it still fails to link for me, and I don't see how it would work as it doesn't set the library search paths as far as I can tell. I also haven't managed to get it working in the latest master anyway, so I'm inclined to say this is a separate issue to discuss

[jcowgill]

Yeah I think all the pkg-config stuff is sorted now. Looks good on the Linux side. 👍