ci: cancel superseded Check runs - #4
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Each ref now has one concurrency group, so pushing again to a PR branch
or landing another merge cancels the run that is already in flight.
The macOS test job takes 3-5 minutes, so without this a burst of pushes
queues several runs whose results are obsolete before they finish.
github.ref keys the group, which keeps refs isolated: pull_request runs
use refs/pull/N/merge and push runs use refs/heads/main, so a merge to
main never cancels an open PR's run, and PRs never cancel each other.
Note this trades away per-commit coverage on main: in a rapid series of
merges only the newest commit keeps a completed run. The tip of main is
always verified; intermediate commits may not be. To keep every main
commit built, make cancellation conditional instead:
cancel-in-progress: ${{ github.event_name == 'pull_request' }}
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Change
The macOS test job runs 3–5 minutes. Without a concurrency group, a burst of
pushes to a PR branch — or several merges in a row — leaves multiple runs
queued whose results are already obsolete by the time they finish. This keeps
one in-flight run per ref and cancels the rest.
Why
github.refkeys the groupRefs stay isolated, which is what makes
cancel-in-progress: truesafe here:github.refpull_requestrefs/pull/N/mergepushto mainrefs/heads/mainSo a merge to
mainnever cancels an open PR's run, and no PR can cancelanother's. Only genuinely superseded runs on the same ref get killed.
Tradeoff worth knowing
This gives up per-commit coverage on
main. In a rapid series of merges, onlythe newest commit keeps a completed run — the tip of
mainis always verified,but intermediate commits may not be, which costs some
git bisectgranularity.That partially offsets the trunk coverage added in #3. If you'd rather keep
every
maincommit built and only dedupe PR runs, change one line:I went with unconditional cancellation since that matches the follow-up as
described, but the conditional form is a defensible default — happy to switch.
Verification
This PR's own run exercises the file. Cancellation behavior only shows up under
concurrent runs, so it isn't directly observable here; the group key is the part
worth reviewing.
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