proposal: cmd/go: allow disabling build cache trimming

[rittneje]

Proposal Details

We have our own docker image containing our Go toolchain. As an optimization, we also pre-compile the standard library (go build std) so that it is in the gocache.

Evidently, the various Go tools will trim the cache upon exit. In particular, they will delete any files in the cache that have not been modified in the last five days. While this may be reasonable for a cache on someone's host machine, it does not make sense for a short-lived container using a cache from its image, since the mtimes will all reflect when the image was built. At best, it trimming the cache is pointless because the container will be destroyed shortly, and at worst is actively counterproductive as those cached files may be used by subsequent commands.

Please add an environment variable to disable trimming the gocache upon command exit. The specific name is immaterial, but something like GOCACHE_AUTO_TRIM=0 would be fine.

[gabyhelp]

Related Issues and Documentation

• cmd/go: clean cache periodically #22642 (closed)
• cmd/go: make cache keys for libraries in GOROOT insensitive to `-trimpath` #57346

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[ianlancetaylor]

CC @matloob

[matloob]

I don't know if this justifies its own environment variable (that would show up in go env, etc.) but maybe we can make it an undocumented # godebug setting?

[rittneje]

@matloob If you mean something we can set via the GODEBUG environment variable, that would also be acceptable. We just need something we can easily configure globally in the base image.

[matloob]

Yes. That is what I mean.

[danp]

I think a possible workaround for this would be to update trim.txt with a time value far in the future so any go command that looks at it will not bother trying to trim.

Something like that could be done at container image build time.

Is that sufficient?

I don't think trim.txt and its usage by the go command are documented / promised but it's something.

[aclements]

I don't think the trim.txt workaround works, because the go command will ignore trim.txt if the timestamp is more than one hour in the future.