[cfe-dev] RFC: Using GitHub Actions for CI testing on the release/* branches

[Tom Stellard via cfe-dev]

Hi,

I would like to start using GitHub Actions[1] for CI testing on the release/*
branches.  As far as I know we don't have any buildbots listening to the
release branches, and I think GitHub Actions are a good way for us to quickly
bring-up some CI jobs there.

My proposal is to start by adding two post-commit CI jobs to the release/9.x branch.
One for building and testing (ninja checka-all) llvm/clang/lld on Linux,
Windows, and Mac, and another for detecting ABI changes since the 9.0.0 release.

I have already implemented these two CI jobs in my llvm-project fork on GitHub[2][3],
but in order to get these running in the main repository, I would need to:

1. Create a new repository in the LLVM organization called 'actions' for storing some custom
builds steps for our CI jobs (see [4]).
2. Commit yaml CI definitions to the .github/workflows directory in the release/9.x
branch.

In the future, I would also like to add buil and tests jobs for other sub-projects
once I am able to get those working.

In addition to being used for post-commit testing, having these CI definitions in the
main tree will make it easier for me (or anyone) to do pre-commit testing for the
release branch in a personal fork.  It will also allow me to experiment with some new
workflows to help make managing the releases much easier.

I think this will be a good way to test Actions in a low traffic environment to
see if they are something we would want to use for CI on the master branch.

Given that we are close to the end of the 9.0.1 cycle, unless there are any
strong objections, I would like to get this enabled by Mon Nov 18, to maximize its
usefulness.  Let me know what you think.

Thanks,
Tom

[1] https://github.com/features/actions
[2] https://github.com/tstellar/llvm-project/commit/952d80e8509ecc95797b2ddbf1af40abad2dcf4e/checks?check_suite_id=305765621
[3] https://github.com/tstellar/llvm-project/commit/6d74f1b81632ef081dffa1e0c0434f47d4954423/checks?check_suite_id=303074176
[4] https://github.com/tstellar/actions