Enable Bzlmod

All but finishes bazelbuild#1482, barring the release and publication to the Bazel
Central Registry. Closes bazelbuild#1625.

New `MODULE.bazel` files mirroring existing `WORKSPACE` configurations
and copies of the `protobuf` toolchainization patch comprise the bulk of
the commit. The empty `WORKSPACE.bzlmod` files ensure that Bzlmod won't
evaluate the existing `WORKSPACE` files.

Reenables the `last_green` Bazel build in CI. Other than that, these new
files comprise the most significant part of the change:

- `.bazelignore`
- `.bcr/*`
- `scala/extensions/config.bzl`
- `scala/extensions/deps.bzl`
- `scala/private/extensions/dev_deps.bzl`
- `scala/private/macros/bzlmod.bzl`

`config.bzl`, `deps.bzl`, and `dev_deps.bzl` are thoroughly tested by
existing tests. These new test files thoroughly test the helpers from
`scala/private/macros/bzlmod.bzl` specifically:

- scala/private/macros/test/...
- test/shell/test_bzlmod_macros.sh

The pattern employed throughout the new module extensions is explained
in the `scala/private/macros/bzlmod.bzl` docstring.

Adding `test/shell/test_bzlmod_macros.sh` also precipitated adding a new
`assert_matches` helper to `test/shell/test_helper.sh`.
`test/shell/test_helper.sh` also introduces a mechanism for
automatically finding and skipping tests, documented in the comment at
the bottom of the file.

"Publish to BCR" configuration in the `.bcr` directory comes from:

- https://github.com/bazel-contrib/publish-to-bcr/tree/main/templates

The bazel-contrib/publish-to-bcr README contains further guidance on
configuring the app.

---

This change enables Bazel 7 and 8 users to migrate their `rules_scala`
dependency from `WORKSPACE` to `MODULE.bazel` whenever they're ready.

Once the Publish to BCR GitHub app is ready, we can use it to publish a
new version to https://registry.bazel.build/. At that point, we can
close bazelbuild#1482.

.bazelci/presubmit.yml

@@ -29,17 +29,15 @@ tasks:
     # Install xmllint
     - sudo apt update && sudo apt install --reinstall libxml2-utils -y
     - "./test_rules_scala.sh"
-  # Switch `last_rc` to `last_green` once Bzlmod lands.
-  # https://github.com/bazelbuild/rules_scala/issues/1482
-  test_rules_scala_linux_last_rc:
-    name: "./test_rules_scala (last_rc Bazel)"
+  test_rules_scala_linux_last_green:
+    name: "./test_rules_scala (last_green Bazel)"
     platform: ubuntu2004
-    bazel: last_rc
+    bazel: last_green
     shell_commands:
     # Install xmllint
     - sudo apt update && sudo apt install --reinstall libxml2-utils -y
     - echo "build --enable_workspace" >> .bazelrc
-    - "./test_rules_scala.sh || buildkite-agent annotate --style 'warning' \"Optional build with last_rc Bazel version failed, [see here](${BUILDKITE_BUILD_URL}#${BUILDKITE_JOB_ID}) (It is not mandatory but worth checking)\""
+    - "./test_rules_scala.sh || buildkite-agent annotate --style 'warning' \"Optional build with last_green Bazel version failed, [see here](${BUILDKITE_BUILD_URL}#${BUILDKITE_JOB_ID}) (It is not mandatory but worth checking)\""
   test_rules_scala_macos:
     name: "./test_rules_scala"
     platform: macos

.bazelignore

@@ -0,0 +1,19 @@
+# Remove once the following is fixed:
+# - bazelbuild/bazel: Loading top-level targets in local_path_override modules
+#   in child directory breaks the build #22208
+#   https://github.com/bazelbuild/bazel/issues/22208
+dt_patches/compiler_sources
+dt_patches/test_dt_patches
+dt_patches/test_dt_patches_user_srcjar
+examples/crossbuild
+examples/overridden_artifacts
+examples/scala3
+examples/semanticdb
+examples/testing/multi_frameworks_toolchain
+examples/testing/scalatest_repositories
+examples/testing/specs2_junit_repositories
+test/proto_cross_repo_boundary/repo
+test_cross_build
+third_party/test/example_external_workspace
+third_party/test/new_local_repo
+third_party/test/proto

.bazelrc

@@ -1,6 +1,5 @@
-# Switch to --noenable_workspace when Bzlmod lands.
-# https://github.com/bazelbuild/rules_scala/issues/1482
-common --enable_workspace --noenable_bzlmod
+# Remove once Bazel 8 becomes the default supported version.
+common --noenable_workspace
 
 # Remove once proto toolchainization becomes the default
 # - https://bazel.build/reference/command-line-reference#flag--incompatible_enable_proto_toolchain_resolution

.bcr/metadata.template.json

@@ -0,0 +1,20 @@
+{
+  "homepage": "https://github.com/bazelbuild/rules_scala",
+  "maintainers": [
+    {
+      "name": "Simonas Pinevičius",
+      "email": "simonas.pinevicius@gmail.com",
+      "github": "simuons"
+    },
+    {
+      "name": "Vaidas Pilkauskas",
+      "email": "vaidas.pilkauskas@gmail.com",
+      "github": "liucijus"
+    }
+  ],
+  "repository": [
+    "github:bazelbuild/rules_scala"
+  ],
+  "versions": [],
+  "yanked_versions": {}
+}

.bcr/presubmit.yml

@@ -0,0 +1,14 @@
+# We recommend included a bcr test workspace that exercises your ruleset with bzlmod.
+# For an example, see https://github.com/aspect-build/bazel-lib/tree/main/e2e/bzlmod.
+bcr_test_module:
+  module_path: "examples/crossbuild"
+  matrix:
+    platform: ["debian10", "macos", "ubuntu2004", "windows"]
+    bazel: [6.x, 7.x]
+  tasks:
+    run_tests:
+      name: "Run test module"
+      platform: ${{ platform }}
+      bazel: ${{ bazel }}
+      test_targets:
+        - "//..."

.bcr/source.template.json

@@ -0,0 +1,5 @@
+{
+  "integrity": "",
+  "strip_prefix": "{REPO}-{VERSION}",
+  "url": "https://github.com/{OWNER}/{REPO}/releases/download/{TAG}/{REPO}-{TAG}.tar.gz"
+}

.github/workflows/workspace_snippet.sh

@@ -4,13 +4,23 @@ set -o errexit -o nounset -o pipefail
 
 # Set by GH actions, see
 # https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
-TAG=${GITHUB_REF_NAME}
-PREFIX="rules_scala-${TAG:1}"
+TAG="${GITHUB_REF_NAME}"
+VERSION="${TAG:1}"
+PREFIX="rules_scala-${VERSION}"
 ARCHIVE="rules_scala-$TAG.tar.gz"
 git archive --format=tar --prefix=${PREFIX}/ ${TAG} | gzip > $ARCHIVE
 SHA=$(shasum -a 256 $ARCHIVE | awk '{print $1}')
 
 cat << EOF
+## Using Bzlmod
+
+Paste this snippet into your \`MODULE.bazel\` file:
+
+\`\`\`starlark
+# Set \`repo_name = "io_bazel_rules_scala"\` if you still need it.
+bazel_dep(name = "rules_scala", version = "${VERSION}")
+\`\`\`
+
 ## Using WORKSPACE
 
 Paste this snippet into your \`WORKSPACE\` file:

.gitignore

@@ -16,3 +16,9 @@ test/semanticdb/tempsrc
 
 # From scripts/create_repository.py
 repository-artifacts.json
+
+# Until it settles down
+**/MODULE.bazel.lock
+
+# Used by some tests, but can also be used for local experimentation.
+tmp/