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authorLaurent Pinchart <laurent.pinchart@ideasonboard.com>2019-07-05 10:36:19 +0300
committerLaurent Pinchart <laurent.pinchart@ideasonboard.com>2019-07-09 12:34:10 +0300
commitc4281ba3bb02f883a9c0980128cfbf3c445e9d89 (patch)
tree862471f099398b67138c8d7e877dd240bbaedfff /Documentation/conf.py
parent0de1a9f318ecf9f3d069b8a4a4a02ef0391cfb04 (diff)
libcamera: Rework automatic version generation to avoid rebuilds
Commit b817bcec6b53 ("libcamera: Auto generate version information") generates version information in order to automatically include it various locations (Sphinx and Doxygen documentation, libcamera::version variable available at runtime, and version.h available at compile time). Unfortunately this causes lots of unnecessary rebuilds when modifying the git tree state, which hinders development. The problem is caused by the generated version.h being listed as a dependency for the whole libcamera. This is required as meson (to the best of my knowledge) doesn't provide a way to explicitly specify the dependency of a single object file (camera_manager.o in this case, as camera_manager.cpp is the only consumer of the generated version string) on the custom target used to generate version.h. The dependency can't be automatically detected at build time, like dependencies on normal headers that are generated by parsing the source, because the version.h header may not exist yet. The build could then fail in a racy way. This change attempts at solving the issue by generating a version.cpp instead of a version.h to set the git-based version. This minimises the number of files that need to be rebuild when then git tree state changes, while retaining the main purpose of the original automatic version generation, the ability to access the git-based version string at runtime. We however lose the ability to access git-based version information at build time in an application building against libcamera, but there is no expected use case for this. The version string is moved from the libcamera namespace to the CameraManager class in order to avoid including version.h inside libcamera (in version.cpp and in camera_manager.cpp), which would create dependencies causing more rebuild steps, as described above. On the other hand, major, minor and patch level version numbers are useful at build time. This commit changes the generation of version.h in order to add three macros named LIBCAMERA_VERSION_MAJOR, LIBCAMERA_VERSION_MINOR and LIBCAMERA_VERSION_PATCH for this purpose. version.h is not included by any other libcamera header or source file, and thus doesn't force a rebuild of the library. The Sphinx and Doxygen documentation keep their git-based version information, which is set during the configuration of the build and then doesn't track git commits. We may want to investigate how to improve this, but given that git-based version for the documentation has very few use cases outside of tagging nightly builds, this isn't considered an issue at the moment. The documentation install directory now uses the base version string, in order to avoid increasing the number of documentation directories needlessly. This shouldn't cause any issue as the API should not change without a change to the version number. The version number generation and handling code now also standardises the version variables to not start with a 'v' prefix in meson, in order to simplify their handling. The prefix is added when generating the relevant files. Note that we go back to specifying the fallback version in the main meson.build, in the call to the project() function. For the time being I believe this should be a good compromise to avoid unnecessary recompilation, and moving the fallback version to a different file for tarball releases can be built on top of this. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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