Add support for bzlmod

[keith]

Fixes #220

[keith]

The hardest part of this integration is to pull in the starlark library from bazel, right now some of the bazel build config is duplicated here, although that should be removable.

Open question: would you be open to dropping the non-bzlmod based build? I haven't touched that yet here, I think we could make both work at once, but we could also delete the old one if it's not necessary with this.

[keith]

It turns out that it's easy enough to keep non-bzlmod working, so I made the minor adjustments required there

[keith]

buildtools isn't in the bcr yet, this repo vendors the downloads directly from that repo's releases

[mering]

Adding links regarding buildtools migration to bzlmod:

• Migrate to Bzlmod for managing external dependencies  bazelbuild/buildtools#1204
• chore(bazel): add MODULE.bazel files for bzlmod bazelbuild/buildtools#1245

[hsudhof]

We currently automatically vendor buildtools from HEAD because we had needs to be pretty close to the edge. I wonder if this can be treated like io_bazel?

[keith]

the problem is that pulling in buildtools that way would require pulling rules_go and resolving the go.mod transitive dependencies of that repo as well.

[hsudhof]

I see. I will look into merging this provided we don't end up with too much version skew for build_tools vs the internal monorepo.

[keith]

sounds good, i don't feel like there are a ton of changes there enough to cause major drift

[keith]

for bzlmod it's better to have a unique name for a repository that might be a dependency of something else, but for building bazel we have to use this name as well, right now these are dup'd but in bzlmod they have a separate set of deps

[hsudhof]

Funnily enough, I have a very similar change in my local repo and ran into exactly the same issue.

[keith]

we've been using this internally for a while, i think it's good to go

[psalaberria002]

This has been pending for a while, could someone review it? It would be very nice to have it merged.

[sin-ack]

Can confirm this works in combination with #233. I did this:

# MODULE.bazel
bazel_dep(name = "copybara", version = "")

# NOTE: This commit is from a PR with Bzlmod support.
# TODO: Replace with a release once it's cut with this PR merged.
git_override(
    module_name = "copybara",
    commit = "791cd9684e28b3bdb7ab4c54dc2e457d8f0b58eb",
    remote = "https://github.com/google/copybara.git",
)

Then just bazel run @copybara//java/com/google/copybara:copybara.

[hsudhof]

Thank you! I will probably remove the wholesale bazel dependency as we only use a tiny part of the codebase that seems suitable for vendoring - just to avoid the churn of the ever growing dependency list.

[keith]

thanks!