cmake: make install path configurable

[junghans]

Making CMake install locations configurable.

I also changed the default for the CMake Target files to share instead of libdir as the library is header-only and arch-independent.

[aprokop]

@junghans Thank you for the contribution!

I'm not really familiar with GNUInstallDirs. When is it useful? Was the current state insufficient for your needs?

Not sure about share/, as my understanding is that it is mostly where documentation, fonts, etc go. For a library, I would not expect it to be found there. Otherwise, it looks fine to me.

[junghans]

I'm not really familiar with GNUInstallDirs. When is it useful? Was the current state insufficient for your needs?

The issue was that things got installed in lib and not lib64, which should be the default for 64-bit system, using GNUInstallDirs instead of a hard-coded lib will fix that.

Not sure about share/, as my understanding is that it is mostly where documentation, fonts, etc go. For a library, I would not expect it to be found there.

CMake is looking into <prefix>/(lib/<arch>|lib*|share)/cmake/<name>*/
(See https://cmake.org/cmake/help/latest/command/find_package.html) so it shouldn't matter much and as your target files are architecture independent share seems the better place.

[aprokop]

it shouldn't matter much and as your target files are architecture independent share seems the better place.

The way I read the Filesystem Hierarchy Standard, share is for non-modifiable data files only, not code:

The /usr/share hierarchy is for all read-only architecture independent data files.

Is there an example of a library that installs code headers in /usr/share or similar?

[junghans]

it shouldn't matter much and as your target files are architecture independent share seems the better place.

The way I read the Filesystem Hierarchy Standard, share is for non-modifiable data files only, not code:

The /usr/share hierarchy is for all read-only architecture independent data files.

Is there an example of a library that installs code headers in /usr/share or similar?

Sorry, it is not about the headers, I only want to change the default for the CMake files from lib to share. Headers go into include by default, are configurable now.

[junghans]

@aprokop I went for the minimal version, as ${CMAKE_INSTALL_DATADIR} is only used for the CMake Modules, one can always just change that default.

[aprokop]

@aprokop I went for the minimal version, as ${CMAKE_INSTALL_DATADIR} is only used for the CMake Modules, one can always just change that default.

This last change goes against what @dalg24 wanted, I think, in that the default location for the cmake/ is now share instead of lib.

[junghans]

@aprokop I went for the minimal version, as ${CMAKE_INSTALL_DATADIR} is only used for the CMake Modules, one can always just change that default.

This last change goes against what @dalg24 wanted, I think, in that the default location for the cmake/ is now share instead of lib.

@dalg24 Does https://discourse.cmake.org/t/what-should-the-destination-be-for-a-header-only-librarys-cmake-config-file/8473 convince you to go with share as a default?

[dalg24]

I don't care too much as long as it is the search paths constructed for both Windows and Unix which both lib* and share are

[aprokop]

Build errors are unrelated.

[aprokop]

@junghans Thank you for your contribution and patience.