On March 20, Kitware released CMake 3.17.
Below are some changes that should improve the life of a Qt developer using CMake.
Ninja Multi-Config Generator
This generator is similar to the Ninja generator but can be used to create multiple configurations at the same time.
This function is similar to the debug_and_release function in qmake.
The reference documentation for the Ninja Multi-Config generator has all the little details.
Using debug_and_release would look like:
cmake -G"Ninja Multi-Config" \ -DCMAKE_CONFIGURATION_TYPES=Release;Debug \ -DCMAKE_DEFAULT_CONFIGS=all \ -DCMAKE_CROSS_CONFIGS=all \ -S source_dir \ -B build_dir cmake --build build_dir
iOS multi-architecture for Ninja/Makefile generators
Now you can compile "fat" (multi-architecture) binaries for iOS right away.
Using the command line would look like:
cmake -GNinja \ -DCMAKE_BUILD_TYPE=Release \ -DCMAKE_SYSTEM_NAME=iOS \ -DCMAKE_OSX_ARCHITECTURES=arm64;x86_64 -S source_dir \ -B build_dir cmake --build build_dir
AUTOGEN uses dependency files of generated moc files
Qt 5.15 brings us an updated moc that can generate a dependency file, which in turn will be used by Ninja to (re)build only the necessary bits.
This means that for a project like Qt Creator, a zero build will be faster since all AUTOGEN targets will no longer need to be built.
With Windows 10 developers tested CMake 3.17, Ninja 1.10, Qt 5.15.0 with Qt Creator and zero builds (5 runs average) went from 4.6 seconds with CMake 3.16 to 2.4 seconds with CMake 3.17 !
Qt Creator still has a few custom targets to accomplish (copying shared files, including files, etc.) and fill those 2.4 seconds.
Ninja does not restart CMake after configuration
You may have noticed that after opening a CMake project in Qt Creator and clicking the "Build" button, Ninja will restart CMake on an already configured project.
Depending on the size of the project or platform, this can be very annoying. Qt Creator CMake configuration can take up to 30 seconds on a Windows 10 development machine.
With Ninja version 1.10 and CMake version 3.17 this annoying behavior is gone!
The Qt SDK includes Ninja and CMake, unfortunately version 1.9 of Ninja and version 3.16 of CMake.
Cache and precompile headers
For projects that use a header file to speed up compilation via precompiled headers and use ccache to cache build artifacts, ccache will now have a 100% cache hit rate!
CMake will copy the header timestamp for its internal precompiled header mechanism and ccache won't think the PCH artifact is too new.
Qt Creator uses the src/shared/qtcreator_gui_pch.h header.
For ccache, include_file_mtime must be specified.
At the moment this only works with GCC. CMake Clang precompile header configuration is not supported by ccache.
Generate healthy zip and 7zip archives
CMake via cmake -E command line tar can extract tar.gz, tar.bz, tar.xz, tar.zstd, zip, 7z archives or create archives.
This can be useful on CI systems where all platforms do not have the necessary tools installed but CMake is installed.
Zip and 7zip archives will contain the current directory. in the archive. While this does not create problems for tar archives, a Zip archive cannot be opened on Windows using Windows Explorer, and a 7zip archive can cause problems (crashes) on KDE.
