CMake: export of targets not used at all in config file

[SpaceIm]

The file created during export of targets should be included in config file, otherwise it's completely useless.

Currently, a downstream project can't link imported target PlayRho (or PlayRho_shared) after a find_package(PlayRho). It ends up linking the raw library through CMake, not the target abstraction, so it's fragile.

Looking at git history, this CMakeLists was cherry picked from an old version of Box2D (when it was more or less broken).

I would advice to:

• [x] Drop this usePlayRho.cmake, it's really an old and terrible way to design a config file.

• [x] Properly install PlayRho-targets.cmake along PlayRhoConfig.cmake (not in a different folder).

• [x] Just write this in PlayRhoConfig.cmake.in (and drop all these non-relocatable variables):

  @PACKAGE_INIT@
  
  include("${CMAKE_CURRENT_LIST_DIR}/PlayRho-targets.cmake")

• [x] Configure this PlayRhoConfig.cmake.in with configure_package_config_file() (from CMakePackageConfigHelpers module).

• [x] Define INCLUDES DESTINATION in install(TARGETS ...) command (so that targets properties are correct in PlayRho-targets.cmake). I guess it should be INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR} (and by the way it would be better to rely on GNUInstallDirs variables instead of hardcoded bin, lib, include names).

• [x] Add a namespace to imported targets (NAMESPACE argument in install(EXPORT ...)), so that imported target could be PlayRho::PlayRho (or PlayRho::PlayRho_shared).

• [x] Add an ALIAS target PlayRho::PlayRho (and PlayRho::PlayRho_shared) for consistency between add_subdirectory(PlayRho) of a vendored PlayRho and find_package(PlayRho) of externally installed PlayRho.

With these suggestions, users will be able to easily consume PlayRho in their project with:

find_package(PlayRho REQUIRED)
target_link_libraries(mytarget PRIVATE PlayRho::PlayRho)

[louis-langholtz]

Hi Spacelm,

Sounds like useful suggestions. Thank you for these!

Do you by chance already have these change suggestions in a branch that you'd like to make a pull request (PR) from? Just asking though. I can make the changes of course but I'm happy to give you credit for them in the form of taking a PR from you.

[louis-langholtz]

I've merged commit ce2b95fae5f394792fa1703e2383fd89a8690725 into the master branch and cherry picked that as commit 4933b021dee8ea12eb72cebb5287b9ea1dd462ba into the release-1.1.1 branch I'm targeting for eventually tagging and releasing as release 1.1.1.