Chandler Carruth a286f38ddc Move CI to use a remote action cache. (#603) ...

The built-in GitHub action cache is too broken for us to use currently.
Pull request runs will evict trunk runs from the cache easily, which
will remove a useful baseline and make builds generally uncached and
extremely slow.

Instead, move to using Bazel's remote caching functionality with a GCP
storage bucket. This gives us nearly limitless storage and is actually
vastly simpler than the prior arrangement. It should also allow cache
sharing between different build configurations and other benefits.

This cache isn't usable by anyone else sadly, but it should at least
provide a better scaling technique for our CI.

This does require us to move from `pull_request` workflow to
a `pull_request_target` workflow and run the CI within the domain of the
project. This is only really safe for us to do while the project remains
private. When we go public we'll want to make the cache publicly
readable and change this code so that when not running on a branch in
the main repository we use the cache in a read-only mode and only write
back updates for branch runs. This should still be effective but
requires a bit more complexity here and in the remote cache including
setting up public access. For now, going with the simple if slightly
less secure model.

2021-06-28 14:47:12 -07:00

..

workflows

Move CI to use a remote action cache. (#603)

2021-06-28 14:47:12 -07:00