Previously, the CI would run upon every label addition, including things
like `builds-mathlib`
or `will-merge-soon`, possibly triggering a new PR release, new mathlib
builds etc. Very wasteful!
Unfortunately (but not surprisingly) Github does not offer a nice way of
saying
“this workflow depends on that label, please re-run if changed”. Not
enough
functional programmer or nix enthusiasts there, I guess…
So here is the next iteration trying to work with what we have from
Github:
A new workflow watches for (only) `full-ci` label addition or deletion,
and then re-runs
the CI job for the current PR.
Sounds simple? But remember, this is github!
* `github.event.pull_request.labels.*.name` is *not* updated when a job
is re-run.
(This is actually a reasonable step towards determinism, but doesn't
help us
constructing this work-around.)
Ok, so let’s use the API to fetch the current state of the label.
* There is no good way to say “find the latest run of workflow `"CI"` on
PR `$n`”.
The best approximation seems to search by branch and triggering event.
This can
probably go wrong if there are multiple PRs from different repos with
the same
head ref name (`patch-1` anyone?). Let’s hope that it doesn’t happen too
often.
* You cannot just rerun a workflow. You can only rerun a finished
workflow. So cancel
it first. And `sleep` a bit…
So let’s see how well this will work. It’s plausibly an improvement.
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