NAME

ycm-faq - YCM FAQ

YCM FAQ

Q: What does YCM means?
A: Originally it was “YARP CMake Modules”, but the name this makes no longer sense, therefore it is now just YCM. See also YCM issue #40

Q: CMake module XXX has a bug/missing feature in CMake version N and has been fixed/updated in CMake version N+1. Can you import the updated module in YCM and make it available for CMake N and older?
A: Yes, just open an issue or a merge request, but see the next question.

Q: Can you actually use any module from a newer version of CMake?
A: No, modules using features that have been added in CMake source code cannot be imported directly. Nonetheless it is possible to supply a patched version of the module that does not use these features.

Q: Why support CMake 3.12?
A: YCM was historically written to support YARP, therefore the supported CMake versions are the same supported by YARP. See YARP Supported Distributions for details.

Q: Can a YCM superbuild build the PackageName package?
A: Probably it can, you will have to supply a BuildPackageName.cmake file with the instructions about how it should be built. You can use YCMEPHelper or ExternalProject to simplify the process. If PackageName is not written using CMake, writing such file might be a bit more difficult, but it can be done.

Q: Why using ExternalProject instead of using git submodules, git externals, svn externals, or similar?
A: ExternalProject supports Git, Subversion, CVS, Mercurial, and zipped files, not just git. Also integrating these tools in a CMake build would require some work anyway, and would make is slower to create a new superbuild project, just writing a CMakeLists.txt file is a lot easier. Also git submodules and git externals in an environment where users do not receive a proper training, introduce more issues than the ones they solve.

Q: The IncludeUrl module is just evil. It could be used to inject any code on your system.
A: That’s why you can check the hash of the file included and why you don’t usually build it as root. If you don’t trust the source you shouldn’t even build the software without checking the source code, but that rarely happens. Also the IncludeUrl module is used only for the bootstrap phase, if YCM is installed on your system, the bootstrap phase will just be skipped. In your code you can just use find_package(YCM REQUIRED) and avoid using it.

Q: Why is the bootstrap phases checking the hashes of the files included in my project?

A: The bootstrap phase also checks that the files used for the bootstrap phase itself are updated, and warns the developer in order to make it easier to keep all the projects synchronized.

Q: How is YCM different from ECM (KDE extra cmake modules)?
A: Conceptually it’s not much different except for support for older CMake releases and bootstrap phase. For some time YCM was also able to bootstrap ECM as well, in order to be able to use ECM modules without installing them. This functionality has been removed for now, but might come back some time in the future.

Q: How is YCM different from catkin?
A: catkin and are very specific for working with ROS and add extra dependencies to your project (i.e. python). Also catkin does a lot of magic, and we didn’t like it when we tried it.

Q: How is YCM different from rosbuild ?
A: rosbuild is deprecated, you should eventually consider using catkin instead.

Q: How is YCM different from Buildyard
A: We were not aware of Buildyard when we started writing YCM. Some of the goals of the projects are very similar, but TODO

October 29, 2021

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