Make bazel_tools work again

[meteorcloudy]

This PR address two problems:

• Partially rolledback ef1a21f to restore android tools extension to avoid breaking older rules_jvm_external and rules_kotlin versions: Fix android_extensions.bzl with Bazel 8.0.0rc1 and later  bazel-contrib/rules_jvm_external#1270
• Add protobuf in MODULE.tools to ensure a Bazel 8 compatible version gets selected. (related Add protobuf dep to bazel_tools #23908)

[ahumesky]

We had a goal of removing all android-related code from the bazel 8 binary, and breaking changes can happen in major versions of bazel. Related to the discussions in bazel-contrib/rules_jvm_external#1270, how far back do we need to support rules_jvm_external? We're working to make rules_android 0.6.0 work with rules_jvm_external and rules_kotlin (or vice versa), blocked on a few issues including the protobuf issue here.

[Wyverald]

that's a good point -- let's fix the protobuf thing first and let the whole android thing pan out, before deciding whether to do the partial //tools/android rollback? I acknowledge the tension between major Bazel versions making breaking changes and rulesets wanting to support older Bazel versions; we should make a conscious decision here before 8.0 release.

[meteorcloudy]

Sounds like there is a egg-chicken problem here.
The new protobuf version depends on rules_jvm_external now, so I actually cannot bump it without fixing the rules_jvm_external issue first.

[Wyverald]

ow. @ahumesky, are you okay with us getting this PR submitted as-is, and then you guys can try to resolve the situation with rules_jvm_external, and then we could maybe roll forward the //tools/android deletion?

[ted-xie]

An important question here is what Bazel RC's the rollbacks/rollforwards would occur in. It would be extra painful to have to wait for RCs to be cut in order for changes to be reflected.

[Wyverald]

If necessary, we can push RCs out very quickly for testing, no problem. (I'm talking multiple in a day.) cc @keertk @iancha1992

[meteorcloudy]

Can we just keep android_extensions.bzl in Bazel 8 and delete it at HEAD? It wouldn't block or slow down any rules_android starlarification work, right?

[ahumesky]

I think it's just an accident that android_extensions.bzl is still in the bazel repo (or we just hadn't gotten to deleting it yet. we were primarily concerned with removing things from the bazel binary before the bazel 8 cut).

Also if we do have to restore android_extensions.bzl in @bazel_tools, think we also have to restore these targets:

bazel/tools/android/android_extensions.bzl

Lines 119 to 123 in 3f70ca1

	"has_androidsdk": attr.label(default = "@bazel_tools//tools/android:always_false"),
	"sdk": attr.label(default = "@bazel_tools//tools/android:poison_pill_android_sdk"),
	"dx_jar_import": attr.label(default = "@bazel_tools//tools/android:no_android_sdk_repository_error"),
	"android_sdk_for_testing": attr.label(default = "@bazel_tools//tools/android:empty"),
	"android_ndk_for_testing": attr.label(default = "@bazel_tools//tools/android:empty"),

The new protobuf version depends on rules_jvm_external now, so I actually cannot bump it without fixing the rules_jvm_external issue first.

Do you mean update protobuf to work with bazel 8?

rules_jvm_external has a goal of being compatible with N-2 versions of bazel (e.g. bazel-contrib/rules_jvm_external#1268 (comment)), but it's not clear that we need to ensure old versions of rules_jvm_external work with new versions of bazel (the compatibility matrix is already very difficult).

Would it work to first land adding the protobuf dep (#23908) which is required for rules_android 0.6.0, then we can update rules_jvm_external for rules_android 0.6.0 (revert bazel-contrib/rules_jvm_external#1215 / restore bazel-contrib/rules_jvm_external@ba7310c, and also this I think bazel-contrib/rules_jvm_external#1268), then we can update rules_kotlin (bazelbuild/rules_kotlin#1205, probably others). Or are there more circular dependencies that prevent all this from working?

[ahumesky]

After discussing this, because of the various circular dependencies we'll need to restore android_extensions.bzl to update all the rulesets for bazel 8

[Wyverald]

@bazel-io fork 8.0.0

[iancha1992]

The changes in this PR have been included in Bazel 8.0.0 RC2. Please test out the release candidate and report any issues as soon as possible.
If you're using Bazelisk, you can point to the latest RC by setting USE_BAZEL_VERSION=8.0.0rc2. Thanks!