CMake: Add option to link with Qt

The named option is BUILD_LINK_WITH_QT, which when set to ON will
generate the QtCreator.ini file needed for Qt Creator to find the
installed Qt.

Change-Id: If3a47a463510fbfc90a314829378c6c4e505d2f7
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

CMakeLists.txt

@@ -24,6 +24,9 @@ set(CMAKE_CXX_EXTENSIONS OFF)
 
 qtc_handle_sccache_support()
 
+option(BUILD_LINK_WITH_QT "Link with Qt from the parent Qt Creator" OFF)
+qtc_link_with_qt()
+
 option(WITH_TESTS "Build Tests" OFF)
 add_feature_info("Build tests" ${WITH_TESTS} "")
 option(WITH_DEBUG_CMAKE "Enabled CMake project debugging functionality (e.g. source file disk checking)" OFF)

cmake/QtCreatorAPIInternal.cmake

@@ -125,6 +125,24 @@ function(qtc_handle_sccache_support)
   endif()
 endfunction()
 
+function(qtc_link_with_qt)
+  # When building with Qt Creator 4.15+ do the "Link with Qt..." automatically
+  if (BUILD_LINK_WITH_QT AND DEFINED CMAKE_PROJECT_INCLUDE_BEFORE)
+    get_filename_component(auto_setup_dir "${CMAKE_PROJECT_INCLUDE_BEFORE}" DIRECTORY)
+    set(qt_creator_ini "${auto_setup_dir}/../QtProject/QtCreator.ini")
+    if (EXISTS "${qt_creator_ini}")
+      file(STRINGS "${qt_creator_ini}" install_settings REGEX "^InstallSettings=.*$")
+      if (install_settings)
+        string(REPLACE "InstallSettings=" "" install_settings "${install_settings}")
+      else()
+        file(TO_CMAKE_PATH "${auto_setup_dir}/.." install_settings)
+      endif()
+      file(WRITE ${CMAKE_BINARY_DIR}/${_IDE_DATA_PATH}/QtProject/QtCreator.ini
+                 "[Settings]\nInstallSettings=${install_settings}")
+    endif()
+  endif()
+endfunction()
+
 function(qtc_enable_release_for_debug_configuration)
   if (MSVC)
     string(REPLACE "/Od" "/O2" CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}")