The absolute path in INCLUDE_INSTALL_DIR eventually made it into the exported MarbleTargets.cmake file in the INTERFACE_INCLUDE_DIRECTORIES target property.

There should be _no_ absolute paths in any outputs of install.

This bug causes the following use-case to fail:

• Make Install marble
• Move/deploy install directory to another location (e.g. deploy from Continuous Integration server)
• Link to Marble from new cmake project with find_package(Marble)

Because of this absolute path, the install directory cannot be moved after it is created.

This is the CMake error:

CMake Error in src/libs/geo/CMakeLists.txt
  Imported target "Marble" includes non-existent path

    "/absolute/path/to/include/dirs/that/doesnt/exist"

  in its INTERFACE_INCLUDE_DIRECTORIES.  Possible reasons include:

  * The path was deleted, renamed, or moved to another location.
  * An install or uninstall procedure did not complete successfully.
  * The installation package was faulty and references files it does not provide.

The following is a minimal example CMakeLists.txt file that can produce the error:

CMakeLists.txt

cmake_minimum_required(VERSION 3.5)
project(Geo VERSION 1.0)
find_package(Marble REQUIRED)
add_executable(geo PRIVATE main.cpp)
target_link_libraries(PUBLIC Marble)

This bug was found while trying to deploy Marble from our Continuous Integration server. To reproduce:

1. Build and install marble
2. Move marble install to a different machine
3. Try to build a cmake project that depends on libMarble

This will fail because the INTERFACE_INCLUDE_DIRECTORIES contained in the generated MarbleTarget.cmake file is not accessible.

Once my patch is applied then the above steps will work correctly.