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chore: use shallow checkout for semver check - #26604
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On pull_request events, the semver check job checks out GitHub's test merge commit, which merges the PR into the base branch as it was when the event fired. The job then fetched the base branch again when it started and used that as the baseline. Jobs currently wait hours for a runner, and in all 59 runs from October 21 and 22, main had moved 2 to 17 commits ahead of the commit the PR was merged into. If main gains a public item in a crate that a waiting PR also changes, the check reports that item as removed by the PR. None of the reports in those runs was wrong, but nothing prevented one. Use the merge commit's first parent as the baseline instead. That is the base branch commit the PR was merged into, so the comparison covers only the PR's changes. The first parent is one generation back, so the checkout needs fetch-depth: 2 rather than the full history of every branch and tag, and the separate fetch of the base branch goes away. In a single-threaded local test, fetching a PR's merge ref at depth 2 took 0.7s of CPU and 16 MB, against 9.2s and 267 MB for the full history. The full-history checkout takes a median of 14s in CI. Tested by fetching refs/pull/26565/merge at depth 2 and running changed_crates.sh against HEAD^1. It lists the same four crates as CI's run for that PR, and semver-check reports the same removed function, register_physical_expr.
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Mostly doing this to save a few cycles in case we want to try running the semver check on |
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Which issue does this PR close?
Rationale for this change
The semver check previously compared the PR against the current state of
apache/main, and did so by doing a fullgitcheckout, including the entire repository history. This approach has two downsides:On (2): when a PR is opened or updated, GitHub creates a test merge commit that merges the PR into main as of that moment (T0). Now suppose that there is a delay between the CI jobs being queued and the semver job actually running, so that when the semver job runs,
HEADis now at T1. The previous version of this check would compare the PR with T1, not T0. For example, if a commit between T0 and T1 added a new API, the semver check would claim that the PR removes that API.Fix this by comparing the merge commit with its first parent instead, which is T0 in the notation above.
What changes are included in this PR?
See above.
What is the testing strategy for this PR?
CI / dev tooling change only. Tested locally on six open PRs (#26565, #26000, #26582, #25874, #26534, #26576): fetched each PR's merge ref at depth 2 and ran both steps against
HEAD^1. The crate lists and semver results match CI, including two PRs that branched 66 and 154 commits behind main.Are there any user-facing changes?
No.