Better documentation/controls to allow CI caching

[thomasvl]

Sorta related to #6865

https://travis-ci.org has support for setting up a directory to be cached/reused between runs. It would seem like for bazel, the good thing to do would be to be able to cache all the remote repo downloads and then likely the action cache.

Looking at Output Directory Layout and bazel help --long startup_options is isn't completely clear how to do this.

The Output Directory Layout page seems to say things will go into ~/.caches/bazel/, as a starting point, but that doesn't seem be true for macOS.

--output_base does seem to control where everything, goes, but this seems to include some log files, which it wouldn't make sense to get cache.

--output_user_root also does seem to control a large chunk of things, but again it includes some log files that likely should be in a cache.

--disk_cache does work, and is reasonable scoped, but we'd still need something for the downloads.

Doing some digging in other rules repos, I did find --experimental_repository_cache, but I can't find that in the help, and it wasn't immediately clear that the value caused anything to be written there.

The Remote Caching page does talk about --disk_cache, but the pages does't seem to cover some of the other things bazel can need to download and maintain locally.

So, can something better document (which make require more options), how to control where downloads are cached to be reused between CI runs? These sorta controls could also be useful to allow the showing of downloads between multiple workspaces on a single machine.

[jin]

--experimental_repository_cache is now --repository_cache and enabled by default. I believe the default value is $HOME/.cache/bazel/_bazel_jingwen/cache/repos/v1/ and all external repos with their checksums explicitly specified in the WORKSPACE are cached. @aehlig did some work here recently.

[ittaiz]

IIRC this works only for rctx.download /download_and_extract with checksums (so no git repository, no maven_jar rule) but does catch many others

…

On Wed, 12 Dec 2018 at 20:53 Jingwen ***@***.***> wrote: --experimental_repository_cache is now --repository_cache and enabled by default. I believe the default value is $HOME/.cache/bazel/_bazel_jingwen/cache/repos/v1/ and all external repos with their checksums explicitly specified in the WORKSPACE are cached. @aehlig <https://github.com/aehlig> did some work here recently. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#6869 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABUIF3fq_iER2c23YV6eZWFVyRHEKlJVks5u4VDGgaJpZM4ZI-Qn> .

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