I think Renato has articulated quite well some concerns I have about this but was unable to express. I would very much prefer if we just focus on using CMake effectively.
Thanks,
Christopher Tetreault
I think Renato has articulated quite well some concerns I have about this but was unable to express. I would very much prefer if we just focus on using CMake effectively.
…
For example, when trying to implement the same logic on both will not be trivial. So, whenever we want to add some functionality or improve how we build LLVM with one system, we’ll have to do so in multiple build systems that do not easily match each other.
Google already does all of this work, and has for years. I think it is fair to say that it hasn’t been a burden on the community.
If we don’t try to match functionality, we’ll segregate the community, because people will be able to do X on build system A but not B, and the similar features cluster together and then we have essentially two projects built from the same source code.
As long as we keep CMake as the canonical system everything will be fine. It works perfectly well today, except that not everyone gets to see or use the bazel files. They exist right now; they work right now; and it hasn’t been a burden on anyone but the people who care about bazel.
Testing this, or worse, trying to fix a buildbot that is built with Bazel (and having to install Java JDK and all its dependencies) on potentially a hardware that you do not have access to, will be a nightmare to debug. The nature of post-commit testing, revert and review of LLVM will not make that simpler. Unless we treat the Bazel build as “not our problem” (which defeats the point of having it?).
Google makes it work like this today, with the rest of the project treating it as “not our problem” because they don’t even see that they exist. The build bot issues would be real, but I think surmountable, given that Google already cleans up the bazel files, it just doesn’t push them. Perhaps an explicit policy that cmake folks don’t have to update the bazel files would be helpful.
To make matters worse, our CMake files are not simple, and do not do all of the things we want them to do in the way we understand completely. There is a lot of kludge that we carry and with that comes in two categories: the things that we hate and would love to fix, and the things that are fixes that we have no idea are there. The former are the reasons why people want to start a new build system, the latter is why they soon realise that was a mistake (insert XKCD joke here).
It wouldn’t be starting a new build system, it would be making a pre-existing, already extremely well functioning one, available to more people.
I can definitely see folks who use cmake not wanting more hassle–that may be a valid reason not to do it. But “it won’t work” or “it’s hard to keep up” or “it’s too complicated” seem well refuted by a multi-year existence proof.
Not seeing Bazel at https://packages.ubuntu.com/.
Glad to see that the current required cmake version is being met with Ubuntu 20.04 and later.
I think Renato has articulated quite well some concerns I have about this but was unable to express. I would very much prefer if we just focus on using CMake effectively.
…
For example, when trying to implement the same logic on both will not be trivial. So, whenever we want to add some functionality or improve how we build LLVM with one system, we’ll have to do so in multiple build systems that do not easily match each other.
Google already does all of this work, and has for years. I think it is fair to say that it hasn’t been a burden on the community.
As far as I can tell, the only burden would be the existence of bazel files in the repo, but scoped within a directory most will never look at and can ignore. The issue of extra files seems of most concern to anyone who is tracking/optimizing repo size or file and commit count.
I can definitely see folks who use cmake not wanting more hassle–that may be a valid reason not to do it.
What would be the hassle to cmake users?
Dave
Nothing that can’t be addressed by policy, such as:
- No public Bazel buildbots blaming them when the build breaks.
- Cmake changes are not reverted to due issues with bazel.
- Requiring that things implemented in bazel also needs to be implemented in cmake. “Things” is somewhat vague here, because there are things that can be done in bazel that can’t be done in cmake. But as long as both systems can build everything (bazel’s power of analysis is much greater), I think this would be acceptable.
That is definitely not what I meant here.