Support asdf's .tool-versions file

changelog/new_support_asdfs_toolversions_file.md

@@ -0,0 +1 @@
+* [#9319](https://github.com/rubocop-hq/rubocop/pull/9319): Support asdf's .tool-versions file. ([@noon-ng][])

config/default.yml

@@ -132,12 +132,13 @@ AllCops:
   # If a value is specified for TargetRubyVersion then it is used. Acceptable
   # values are specificed as a float (i.e. 2.5); the teeny version of Ruby
   # should not be included. If the project specifies a Ruby version in the
-  # .ruby-version file, Gemfile or gems.rb file, RuboCop will try to determine
-  # the desired version of Ruby by inspecting the .ruby-version file first,
-  # followed by the Gemfile.lock or gems.locked file. (Although the Ruby version
-  # is specified in the Gemfile or gems.rb file, RuboCop reads the final value
-  # from the lock file.) If the Ruby version is still unresolved, RuboCop will
-  # use the oldest officially supported Ruby version (currently Ruby 2.4).
+  # .tool-versions or .ruby-version files, Gemfile or gems.rb file, RuboCop will
+  # try to determine the desired version of Ruby by inspecting the
+  # .tool-versions file first, then .ruby-version, followed by the Gemfile.lock
+  # or gems.locked file. (Although the Ruby version is specified in the Gemfile
+  # or gems.rb file, RuboCop reads the final value from the lock file.) If the
+  # Ruby version is still unresolved, RuboCop will use the oldest officially
+  # supported Ruby version (currently Ruby 2.4).
   TargetRubyVersion: ~
   # Determines if a notification for extension libraries should be shown when
   # rubocop is run. Keys are the name of the extension, and values are an array

lib/rubocop/target_ruby.rb

@@ -44,33 +44,61 @@ def find_version
     # The target ruby version may be found in a .ruby-version file.
     # @api private
     class RubyVersionFile < Source
-      FILENAME = '.ruby-version'
+      RUBY_VERSION_FILENAME = '.ruby-version'
+      RUBY_VERSION_PATTERN = /\A(?:ruby-)?(?<version>\d+\.\d+)/.freeze
 
       def name
-        "`#{FILENAME}`"
+        "`#{RUBY_VERSION_FILENAME}`"
       end
 
       private
 
+      def filename
+        RUBY_VERSION_FILENAME
+      end
+
+      def pattern
+        RUBY_VERSION_PATTERN
+      end
+
       def find_version
-        file = ruby_version_file
+        file = version_file
         return unless file && File.file?(file)
 
-        # rubocop:disable Lint/MixedRegexpCaptureTypes
-        # `(ruby-)` is not a capture type.
-        File.read(file).match(/\A(ruby-)?(?<version>\d+\.\d+)/) do |md|
-          # rubocop:enable Lint/MixedRegexpCaptureTypes
+        File.read(file).match(pattern) do |md|
           md[:version].to_f
         end
       end
 
-      def ruby_version_file
-        @ruby_version_file ||=
-          @config.find_file_upwards(FILENAME,
+      def version_file
+        @version_file ||=
+          @config.find_file_upwards(filename,
                                     @config.base_dir_for_path_parameters)
       end
     end
 
+    # The target ruby version may be found in a .tool-versions file, in a line
+    # starting with `ruby`.
+    # @api private
+    class ToolVersionsFile < RubyVersionFile
+      TOOL_VERSIONS_FILENAME = '.tool-versions'
+      TOOL_VERSIONS_PATTERN = /\Aruby (?:ruby-)?(?<version>\d+\.\d+)/.freeze
+
+      def name
+        "`#{TOOL_VERSIONS_FILENAME}`"
+      end
+
+      private
+
+      def filename
+        TOOL_VERSIONS_FILENAME
+      end
+
+      def pattern
+        TOOL_VERSIONS_PATTERN
+      end
+    end
+
     # The lock file of Bundler may identify the target ruby version.
     # @api private
     class BundlerLockFile < Source
@@ -194,7 +222,15 @@ def self.supported_versions
       KNOWN_RUBIES
     end
 
-    SOURCES = [RuboCopConfig, RubyVersionFile, BundlerLockFile, GemspecFile, Default].freeze
+    SOURCES = [
+      RuboCopConfig,
+      RubyVersionFile,
+      ToolVersionsFile,
+      BundlerLockFile,
+      GemspecFile,
+      Default
+    ].freeze
+
     private_constant :SOURCES
 
     def initialize(config)

spec/rubocop/target_ruby_spec.rb

@@ -96,13 +96,45 @@
         end
       end
 
-      it 'does not read Gemfile.lock or gems.locked' do
+      it 'does not read .tool-versions, Gemfile.lock or gems.locked' do
+        expect(File).not_to receive(:file?).with('.tool-versions')
         expect(File).not_to receive(:file?).with('Gemfile')
         expect(File).not_to receive(:file?).with('gems.locked')
         target_ruby.version
       end
     end
 
+    context 'when .tool-versions is present' do
+      before do
+        dir = configuration.base_dir_for_path_parameters
+        create_file(File.join(dir, '.tool-versions'), tool_versions)
+      end
+
+      context 'when .tool-versions contains a ruby version' do
+        let(:tool_versions) { ['ruby 3.0.0', 'nodejs 14.9.0'] }
+        let(:ruby_version_to_f) { 3.0 }
+
+        it 'reads it to determine the target ruby version' do
+          expect(target_ruby.version).to eq ruby_version_to_f
+        end
+
+        it 'does not read Gemfile.lock, gems.locked' do
+          expect(File).not_to receive(:file?).with(/Gemfile/)
+          expect(File).not_to receive(:file?).with(/gems\.locked/)
+          target_ruby.version
+        end
+      end
+
+      context 'when .tool-versions does not contain a ruby version' do
+        let(:tool_versions) { ['nodejs 14.9.0'] }
+        let(:ruby_version_to_f) { 3.0 }
+
+        it 'uses the default ruby version' do
+          expect(target_ruby.version).to eq default_version
+        end
+      end
+    end
+
     context 'when .ruby-version is not present' do
       ['Gemfile.lock', 'gems.locked'].each do |file_name|
         context "and #{file_name} exists" do