Specifying client config.json with Bazel label

[linzhp]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

The client_config attribute of docker_toolchain_configure only accepts an absolute path to a directory. This is not portable, because absolute paths are machine dependent.

Issue Number: N/A

What is the new behavior?

Allow the client_config attribute of docker_toolchain_configure to accept a Bazel label to the config.json file, so we can check the file into a repository and check out the repository anywhere.

Does this PR introduce a breaking change?

• Yes
• No

Other information

Ideally, we should declare docker_client_config attribute of container_pull as a label instead of a string, so the changes in the content of client config will invalidate the cache and trigger a rebuild. However, this will be a backward-incompatible change, as absolute paths will no longer work. What do you think?

[gravypod]

This looks good. Is there any specific use case you're attempting to satisfy here @linzhp?

[linzhp]

Yes, we want to configure the credHelpers in config.json, so we can access our internal docker registry with a custom authentication, but we don't want require all dev and CI machines to check out our repository in exactly the same location. So we hope to have something like:

    docker_toolchain_configure(
        name = "docker_config",
        client_config = "@//third_party/docker/registry/config:config.json",
    )

[linzhp]

@gravypod What's the process to merge a PR after getting approved? I saw #2000 was also approved, but not merged for a long time.

[gravypod]

Thanks @linzhp. Just wanted to get a "reason" on the issue so that when someone Googles "how do I X rules_docker" they find this page :)