Extended CMake installation handling (#523)

* updated the version handling

- Introduces a new version.txt file
- This file is parsed by CMake to determine the current version

* assign version in project call

* use version variable

* Meson update

1. Minor fix for GCC build
2. Use external version file which can be used by CMake as well

* get version from git tag now

* ci/cd broke..

* maybe this solves the error

* updated workflow files

* one last test

* remove git describe call

* extended CMake installation handling

* only write version file if possible

* read version.txt as fallback

* missing version.txt arg

CMakeLists.txt

@@ -16,16 +16,44 @@ add_library(${PROJECT_NAME} INTERFACE)
 
 target_include_directories(${PROJECT_NAME} SYSTEM INTERFACE
         $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
-        $<INSTALL_INTERFACE:include>
+        $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
         )
 
 target_link_libraries(${PROJECT_NAME} INTERFACE)
 
 # only install if top level project
 if(${CMAKE_PROJECT_NAME} STREQUAL ${PROJECT_NAME})
-   install(TARGETS ${PROJECT_NAME}  EXPORT ${PROJECT_NAME}Config)
-   install(EXPORT ${PROJECT_NAME}Config  DESTINATION lib/cmake/${PROJECT_NAME})
-   install(DIRECTORY include/${PROJECT_NAME}  DESTINATION include)
+    # Steps here based on excellent guide: https://dominikberner.ch/cmake-interface-lib/
+    # Which also details all steps
+    include(CMakePackageConfigHelpers)
+    install(TARGETS ${PROJECT_NAME}
+        EXPORT ${PROJECT_NAME}Targets
+        ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+    )
+    if(ETL_VERSION)
+        # Generate the package configuration files using CMake provided macros
+        write_basic_package_version_file(
+            "${PROJECT_NAME}ConfigVersion.cmake"
+            COMPATIBILITY SameMajorVersion
+        )
+    endif()
+    configure_package_config_file(
+        "${PROJECT_SOURCE_DIR}/cmake/${PROJECT_NAME}Config.cmake.in"
+        "${PROJECT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
+        INSTALL_DESTINATION
+        ${CMAKE_INSTALL_DATAROOTDIR}/${PROJECT_NAME}/cmake)
+
+    # Install target file, then package configuration files, and finally the headers
+    install(EXPORT ${PROJECT_NAME}Targets
+        FILE ${PROJECT_NAME}Targets.cmake
+        NAMESPACE ${PROJECT_NAME}::
+        DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/${PROJECT_NAME}/cmake)
+    install(FILES "${PROJECT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
+        "${PROJECT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake"
+        DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/${PROJECT_NAME}/cmake)
+    install(DIRECTORY ${PROJECT_SOURCE_DIR}/include/etl DESTINATION include)
 endif()
 
 if (BUILD_TESTS)

cmake/etlConfig.cmake.in

@@ -0,0 +1,4 @@
+@PACKAGE_INIT@
+
+include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Targets.cmake")
+check_required_components("@PROJECT_NAME@")