A way to cache reproducible extension results between bazel server restarts

[jkurland-roku]

Description of the feature request:

No response

Which category does this issue belong to?

Core, External Dependency

What underlying problem are you trying to solve with this feature?

Currently extensions marked as reproducible are rerun more than they need to since they aren't tracked in the lock file. Since some extensions are slow it would be useful to have a mechanism to skip running them.

Which operating system are you running Bazel on?

ubuntu

What is the output of bazel info release?

release 8.0.0

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse HEAD ?

No response

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

No response

[fmeum]

https://docs.google.com/document/d/1TjA7-M5njkI1F38IC0pm305S9EOmxcUwaCIvaSmansg/edit?usp=drivesdk included an "always update" lockfile under the output base for reproducible extensions. We didn't implement it at the time simply because we didn't have examples of slow but reproducible extensions. Now that we do, I think that we should implement this.

@Wyverald @meteorcloudy What do you think?

[meteorcloudy]

I think it's a good idea, I guess bazel clean --expunge should still nuke it?

[fmeum]

Yes, it would behave similar to the local action cache and be stored directly under the output base.

[meteorcloudy]

Happy to review a PR!

[Wyverald]

SGTM!

Now that we do, I think that we should implement this.

Just for the record, what are some examples of slow but reproducible extensions?

[fmeum]

rules_rust's crate_universe is the example: https://bazelbuild.slack.com/archives/CSV56UT0F/p1734442667932509