Improve shared configuration syncing.

- Improve code style to match `brew style` norms.
- General code refactoring/cleanup.
- Fail script on invalid parameters.
- Provide custom handling for `.rubocop.yml` and `.ruby-version` from
  Homebrew/brew's repository. We want to match the RuboCop and
  (Portable) Ruby version (without revision) usage from there.
- Ensure that this workflow is always tested (but PRs not created) when
  triggered by a pull request.
- Check code style with `brew style` in CI.

.github/actions/sync/shared-config.rb

@@ -1,59 +1,80 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
 
-require 'fileutils'
-require 'open3'
-require 'pathname'
+require "English"
+require "fileutils"
+require "open3"
+require "pathname"
 
+# This makes sense for a standalone script.
+# rubocop:disable Style/TopLevelMethodDefinition
 def git(*args)
-  system 'git', *args
-  exit $?.exitstatus unless $?.success?
+  system "git", *args
+  exit $CHILD_STATUS.exitstatus unless $CHILD_STATUS.success?
 end
+# rubocop:enable Style/TopLevelMethodDefinition
 
-target_dir = Pathname(ARGV[0])
-source_dir = ARGV[1]
+target_directory = ARGV[0]
+target_directory_path = Pathname(target_directory)
+homebrew_directory_path = Pathname(ARGV[1])
 
-puts 'Detecting changes…'
+if !target_directory_path.directory? || !homebrew_directory_path.directory? || ARGV[2]
+  abort "Usage: #{$PROGRAM_NAME} <target_directory_path> <homebrew_directory_path>"
+end
+
+ruby_version = ".ruby-version"
+rubocop_yml = ".rubocop.yml"
+
+homebrew_ruby_version =
+  (homebrew_directory_path/"Library/Homebrew/vendor/portable-ruby-version").read.chomp.sub(/_\d+$/, "")
+homebrew_rubocop_config = homebrew_directory_path/"Library/Homebrew/#{rubocop_yml}"
+
+puts "Detecting changes…"
 [
-  '.github/workflows/lock-threads.yml',
-  '.github/workflows/stale-issues.yml',
-  '.ruby-version',
-].each do |glob|
-  src_paths = Pathname.glob(glob)
-  dst_paths = Pathname.glob(target_dir.join(glob))
-
-  dst_paths.each do |path|
-    FileUtils.rm_f path
-  end
+  ruby_version,
+  rubocop_yml,
+  ".github/workflows/lock-threads.yml",
+  ".github/workflows/stale-issues.yml",
+].each do |file|
+  FileUtils.rm_f file
+
+  target_path = target_directory_path/file
+  target_path.dirname.mkpath
 
-  src_paths.each do |path|
-    target_dir.join(path.dirname).mkpath
-    FileUtils.cp path, target_dir.join(path)
+  case file
+  when ruby_version
+    path.write("#{homebrew_ruby_version}\n")
+  when rubocop_yml
+    FileUtils.cp homebrew_rubocop_config, path
+  else
+    FileUtils.cp file, target_path
   end
 end
 
-out, err, status = Open3.capture3('git', '-C', target_dir.to_s, 'status', '--porcelain', '--ignore-submodules=dirty')
+out, err, status = Open3.capture3("git", "-C", target_directory, "status", "--porcelain", "--ignore-submodules=dirty")
 raise err unless status.success?
 
-target_dir_changed = !out.chomp.empty?
+target_directory_path_changed = !out.chomp.empty?
 
-unless target_dir_changed
-  puts 'No changes detected.'
+unless target_directory_path_changed
+  puts "No changes detected."
   exit
 end
 
-git '-C', target_dir.to_s, 'add', '--all'
+git "-C", target_directory, "add", "--all"
 
-out, err, status = Open3.capture3('git', '-C', target_dir.to_s, 'diff', '--name-only', '--staged')
+out, err, status = Open3.capture3("git", "-C", target_directory, "diff", "--name-only", "--staged")
 raise err unless status.success?
 
 modified_paths = out.lines.map(&:chomp)
 
 modified_paths.each do |modified_path|
   puts "Detected changes to #{modified_path}."
-  git '-C', target_dir.to_s, 'commit', modified_path, '--message', "#{File.basename(modified_path)}: update to match main configuration", '--quiet'
+  git "-C", target_directory, "commit", modified_path, "--message",
+      "#{File.basename(modified_path)}: update to match main configuration", "--quiet"
 end
 puts
 
-File.open(ENV.fetch('GITHUB_OUTPUT'), 'a') do |f|
-  f.puts 'pull_request=true'
+File.open(ENV.fetch("GITHUB_OUTPUT"), "a") do |f|
+  f.puts "pull_request=true"
 end

.github/workflows/sync-shared-config.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - master
+  pull_request:
 
 permissions:
   contents: read
@@ -45,6 +46,12 @@ jobs:
           - Homebrew/rubydoc.brew.sh
       fail-fast: false
     steps:
+      - name: Set up Homebrew
+        id: set-up-homebrew
+        uses: Homebrew/actions/setup-homebrew@master
+
+      - run: brew style .github/actions/sync/*.rb
+
       - name: Clone main repository
         uses: actions/checkout@v4
         with:
@@ -71,10 +78,10 @@ jobs:
         id: detect_changes
         env:
           HOMEBREW_GPG_PASSPHRASE: ${{ secrets.BREWTESTBOT_GPG_SIGNING_SUBKEY_PASSPHRASE }}
-        run: ./.github/actions/sync/shared-config.rb 'vendor/${{ matrix.repo }}' '${{ matrix.repo }}' 'sync-shared-config'
+        run: ./.github/actions/sync/shared-config.rb 'vendor/${{ matrix.repo }}' '${{ steps.set-up-homebrew.outputs.repository-path }}'
 
       - name: Create pull request
-        if: ${{ steps.detect_changes.outputs.pull_request == 'true' }}
+        if: ${{ github.ref == 'refs/heads/master' && steps.detect_changes.outputs.pull_request == 'true' }}
         uses: peter-evans/create-pull-request@6d6857d36972b65feb161a90e484f2984215f83e
         with:
           path: vendor/${{ matrix.repo }}

.rubocop.yml

@@ -0,0 +1,80 @@
+inherit_from:
+  - ../.rubocop.yml
+
+Bundler/GemFilename:
+  Enabled: false
+
+Homebrew/MoveToExtendOS:
+  Enabled: true
+  Exclude:
+    - "{extend,test,requirements}/**/*"
+    - "os.rb"
+
+Naming/PredicateName:
+  inherit_mode:
+    merge:
+      - AllowedMethods
+  AllowedMethods:
+    - is_32_bit?
+    - is_64_bit?
+
+# Only enforce documentation for public APIs.
+# Checked by the tests.yml syntax job
+Style/Documentation:
+  AllowedConstants:
+    - Homebrew
+  Include:
+    - cask/cask.rb
+    - cask/dsl.rb
+    - cask/dsl/version.rb
+    - cask/url.rb
+    - development_tools.rb
+    - download_strategy.rb
+    - extend/ENV/super.rb
+    - extend/kernel.rb
+    - extend/pathname.rb
+    - formula.rb
+    - formula_assertions.rb
+    - formula_free_port.rb
+    - language/go.rb
+    - language/java.rb
+    - language/node.rb
+    - language/perl.rb
+    - language/python.rb
+    - livecheck/strategy/apache.rb
+    - livecheck/strategy/bitbucket.rb
+    - livecheck/strategy/cpan.rb
+    - livecheck/strategy/crate.rb
+    - livecheck/strategy/extract_plist.rb
+    - livecheck/strategy/git.rb
+    - livecheck/strategy/github_latest.rb
+    - livecheck/strategy/github_releases.rb
+    - livecheck/strategy/gnome.rb
+    - livecheck/strategy/gnu.rb
+    - livecheck/strategy/hackage.rb
+    - livecheck/strategy/json.rb
+    - livecheck/strategy/launchpad.rb
+    - livecheck/strategy/npm.rb
+    - livecheck/strategy/page_match.rb
+    - livecheck/strategy/pypi.rb
+    - livecheck/strategy/sourceforge.rb
+    - livecheck/strategy/sparkle.rb
+    - livecheck/strategy/xml.rb
+    - livecheck/strategy/xorg.rb
+    - livecheck/strategy/yaml.rb
+    - os.rb
+    - resource.rb
+    - utils/inreplace.rb
+    - utils/shebang.rb
+    - utils/string_inreplace_extension.rb
+    - version.rb
+    - tap.rb
+
+Homebrew/NegateInclude:
+  Exclude:
+    # YARD runs stand-alone.
+    - yard/docstring_parser.rb
+
+Style/DocumentationMethod:
+  Include:
+    - "formula.rb"