Add file locking to dir cache - #3573
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toastwaffle
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Aug 20, 2026
Co-authored-by: Samuel Littley <samuel.littley@toastwaffle.com>
peterebden
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Aug 23, 2026
Stacked on #3573 Now the cache is threadsafe, we can share it between e2e tests. It's not super obvious but these have slowed down a _lot_ over time - as they moved to `plz_repo_e2e_test` which is better separated but rebuilds more, plugins added more downloads and (most significantly) we now build the Go stdlib in tree rather than assuming it's on the system. This isn't so bad on a powerful machine but it is bad on a weaker one (i.e. all the CI machines). I've also rationalised some of the plugin / Go versions in there. There is possibly some future work to keep all these better aligned with the parent repo - honestly we usually just forget (hence 10 version old plugins and Go 1.24). I've added the cache to CircleCI as well; otherwise it will always be cold, and we can't deduplicate the work between everything in that case, so we'd get no benefit without.
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This should make it safer to run concurrent processes without them corrupting the shared cache.
I'm going to have a look at sharing it between the e2e tests, which are very slow on weaker machines (like CI) because they heavily rebuild the Go stdlib. That's nontrivial though so I will leave for a separate PR.