feat: add RuboCop linter support for Ruby

[cgrindel]

Summary

Adds support for RuboCop linter for Ruby code in rules_lint, following the established patterns for language-specific linters (similar to flake8 for Python and eslint for JavaScript).

Implementation

Core Features

• RuboCop linter aspect (lint/rubocop.bzl) that visits rb_binary, rb_library, and rb_test rules
• Bundler integration with rules_ruby for hermetic gem management
• SARIF report generation for machine-readable output
• Fix mode support with --autocorrect-all via patcher helper
• Color output support with RUBOCOP_FORCE_COLOR environment variable

Architecture

• Uses rules_ruby's bundle_fetch() to manage RuboCop gem dependencies
• Pinned to RuboCop 1.81.1 via Gemfile.lock for reproducible builds
• Properly registers Ruby toolchains for Bazel integration
• Handles sandbox permissions with XDG_CACHE_HOME workaround

Java Runtime Requirements

• JRuby 10.0.2.0 requires Java 21 or higher
• Example includes Java 21 configuration (example/tools/java21.bazelrc)
• Gemfile.lock generated with Java platform support (universal-java, universal-java-21)
• Java-specific gem versions avoid C extension compilation in Bazel sandbox

Example Configuration

Gemfile:

gem "rubocop", "~> 1.50"

.ruby-version:

jruby-10.0.2.0

MODULE.bazel:

ruby = use_extension("@rules_ruby//ruby:extensions.bzl", "ruby")
ruby.toolchain(
    name = "ruby",
    version_file = "//:.ruby-version",
)
ruby.bundle_fetch(
    name = "bundle",
    gem_checksums = {
        # ... gem checksums including Java-specific versions
        "json-2.15.1-java": "a6185eebe724a6937f60729e4998276d6b3de3ecc35be34f8e47c1eb40903ecf",
        "racc-1.8.1-java": "54f2e6d1e1b91c154013277d986f52a90e5ececbe91465d29172e49342732b98",
    },
    gemfile = "//:Gemfile",
    gemfile_lock = "//:Gemfile.lock",
)

tools/lint/linters.bzl:

load("@aspect_rules_lint//lint:rubocop.bzl", "lint_rubocop_aspect")

rubocop = lint_rubocop_aspect(
    binary = "//tools/lint:rubocop",
    configs = ["//:rubocop.yml"],
)

Testing

• Added example Ruby file with intentional violations (example/src/hello.rb)
• Integration test in example/test:rubocop (marked manual, expected to fail)
• Updated example/test/lint_test.bats to verify RuboCop output
• Verified linter detects 12 offenses including:
  • Missing frozen string literal comment
  • Unused variable assignments
  • String literal style violations
  • Line length violations
  • Indentation issues

🤖 Generated with Claude Code

[aspect-workflows]

Test

All tests were cache hits

5 tests (100.0%) were fully cached saving 2s.

---

Test

example

8 test targets passed

Targets

//tools/format:format_test_HTML_Jinja_with_djlint [k8-fastbuild]3s
//tools/format:format_test_JavaScript_with_prettier [k8-fastbuild]17s
//tools/format:format_test_Markdown_with_prettier [k8-fastbuild]3s
//tools/format:format_test_Protocol_Buffer_with_buf [k8-fastbuild]814ms
//tools/format:format_test_Python_with_ruff [k8-fastbuild]447ms
//tools/format:format_test_SQL_with_prettier [k8-fastbuild]2s
//tools/format:format_test_Scala_with_scalafmt [k8-fastbuild]5s
//tools/format:format_test_Starlark_with_buildifier [k8-fastbuild]416ms

Total test execution time was 32s. 33 tests (80.5%) were fully cached saving 14s.

---

Test (WORKSPACE) (Test)

example

8 test targets passed

Targets

//tools/format:format_test_HTML_Jinja_with_djlint [k8-fastbuild]3s
//tools/format:format_test_JavaScript_with_prettier [k8-fastbuild]8s
//tools/format:format_test_Markdown_with_prettier [k8-fastbuild]1s
//tools/format:format_test_Protocol_Buffer_with_buf [k8-fastbuild]656ms
//tools/format:format_test_Python_with_ruff [k8-fastbuild]240ms
//tools/format:format_test_SQL_with_prettier [k8-fastbuild]976ms
//tools/format:format_test_Scala_with_scalafmt [k8-fastbuild]4s
//tools/format:format_test_Starlark_with_buildifier [k8-fastbuild]238ms

Total test execution time was 19s. 13 tests (61.9%) were fully cached saving 8s.

---

Lint [.]      Lint [example]

[alexeagle]

Nice, could you update lint-test.bats also, similar to https://github.com/aspect-build/rules_lint/pull/641/files ?

[cgrindel]

@alexeagle I think this PR is ready for review. I noticed the CI / aspect timed out. Is there something that I need to address there?