Provide a flag preset for bazel-contrib/bazelrc-preset.bzl

[hofbi]

Is your feature request related to a problem? Please describe.
https://github.com/bazel-contrib/bazelrc-preset.bzl is a new tool how to handle bazel presets. https://github.com/tweag/credential-helper?tab=readme-ov-file#installation-and-usage defines a good amount of flags that users should define in their bazelrc. That could be more convenient.

Describe the solution you'd like
As we are documenting with bazel-contrib/bazelrc-preset.bzl#68 and what has been already done in aspect-build/toolchains_protoc#84 shows how bazelrc-preset.bzl can be used for this and I think this project is a good candidate.

Describe alternatives you've considered
Not doing it a leave everything as is.

[malt3]

Hey, thanks for creating this issue.
It sounds like a reasonable request that would improve the quality of life for our users.

We are currently a bit short on time we can invest into these kinds of contributions, so I'll add it to our backlog and work on it eventually.
If you or anyone else wants to take a stab in the meantime, I'm always happy to review your PRs!

[bthmc]

Thanks for the good idea, @hofbi ! I evaluated bazelrc-preset.bzl, in the context of tweag-credential-helper, and found two issues:

1. While the credential helper README.md lists several default flag values, in practice, a user would only use a single pair of them (unix+windows), for the particular credential provider the user actually uses. There's little point to specify all the other flags.
2. Suppose we still want to provide a CREDENTIAL_HELPER_FLAGS variable, that sets all those flags. We need to specify the --credential_helper cli argument multiple times (twice for each provider). Unfortunately, bazelrc_preset extra_presets takes a flag keyed dict, we can't pass the same argument multiple times (at least, that's my understanding). The closest we could get is CREDENTIAL_HELPER_FLAG_WIN_S3, CREDENTIAL_HELPER_FLAGS_UNIX_S3, CREDENTIAL_HELPER_FLAGS_WIN_WIN_GITHUB, etc., but I don't see the usefulness of that. Furthermore, such flags cannot be combined (dict | dict would swallow all but one of them), making it a source of major user confusion.

I'm closing this, please do reopen if my understanding is flawed, and suggest a solution. Thanks.

[hofbi]

Good point, I created bazel-contrib/bazelrc-preset.bzl#72 and might come back to reopen once we support this.

[hofbi]

@bthmc https://github.com/bazel-contrib/bazelrc-preset.bzl/releases/tag/v1.2.0 is now available on BCR and includes bazel-contrib/bazelrc-preset.bzl#72 to support multiple flags and even test that the flag presets are valid. See aspect-build/toolchains_protoc#96 as an example how this looks like in action.