Replace `method_source` gem with stdlib equivalent

The `method_source` gem was added in
https://github.com/rails/rails/pull/19216. It was used to determine the
last line number of a given test method to support running tests by line
number. But this is not something that requires an external dependency:
Ripper can do this easily, and it has the added advantage of not using
repeated calls to `eval` to do it.

Drop `method_source` and replace it with a simple handler for Ripper's
`on_def` parser event.

I don't believe that there are any mainstream rubies at this point that
can run Rails and don't support Ripper but correct me if I'm wrong.

Gemfile.lock

@@ -94,7 +94,6 @@ PATH
     railties (7.1.0.alpha)
       actionpack (= 7.1.0.alpha)
       activesupport (= 7.1.0.alpha)
-      method_source
       rake (>= 12.2)
       thor (~> 1.0)
       zeitwerk (~> 2.6)
@@ -315,7 +314,6 @@ GEM
     marcel (1.0.2)
     matrix (0.4.2)
     memoist (0.16.2)
-    method_source (1.0.0)
     mini_magick (4.11.0)
     mini_mime (1.1.2)
     mini_portile2 (2.8.0)

railties/lib/rails/test_unit/runner.rb

@@ -1,10 +1,10 @@
 # frozen_string_literal: true
 
 require "shellwords"
-require "method_source"
 require "rake/file_list"
 require "active_support"
 require "active_support/core_ext/module/attribute_accessors"
+require "ripper"
 
 module Rails
   module TestUnit
@@ -169,10 +169,33 @@ module Rails
       private
         def definition_for(method)
           file, start_line = method.source_location
-          end_line = method.source.count("\n") + start_line - 1
+          end_line = MethodEndFinder.call(source: File.read(file), target: method.name)
 
           return file, start_line..end_line
         end
+
+        # Finds the line number where the definition of method named +target+ ends.
+        module MethodEndFinder # :nodoc:
+          def self.call(source:, target:)
+            catch(:line_number_is) do
+              DefParser.new(source: source, target: target).parse
+              return nil
+            end
+          end
+
+          class DefParser < Ripper # :nodoc:
+            def initialize(source:, target:)
+              @target = String(target)
+              super(source)
+            end
+
+            def on_def(method_name, *)
+              if method_name == @target
+                throw(:line_number_is, lineno)
+              end
+            end
+          end
+        end
     end
   end
 end

railties/railties.gemspec

@@ -42,7 +42,6 @@ Gem::Specification.new do |s|
 
   s.add_dependency "rake", ">= 12.2"
   s.add_dependency "thor", "~> 1.0"
-  s.add_dependency "method_source"
   s.add_dependency "zeitwerk", "~> 2.6"
 
   s.add_development_dependency "actionview", version

railties/test/application/test_runner_test.rb

@@ -376,7 +376,7 @@ module ApplicationTests
       end
     end
 
-    def test_more_than_one_line_filter
+    def test_more_than_one_line_filter_macro_syntax
       app_file "test/models/post_test.rb", <<-RUBY
         require "test_helper"
 
@@ -404,6 +404,34 @@ module ApplicationTests
       end
     end
 
+    def test_more_than_one_line_filter_test_method_syntax
+      app_file "test/models/post_test.rb", <<-RUBY
+        require "test_helper"
+
+        class PostTest < ActiveSupport::TestCase
+          def test_first_filter
+            puts 'PostTest:FirstFilter'
+            assert true
+          end
+
+          def test_second_filter
+            puts 'PostTest:SecondFilter'
+            assert true
+          end
+
+          def test_line_filter_does_not_run_this
+            assert true
+          end
+        end
+      RUBY
+
+      run_test_command("test/models/post_test.rb:4:9").tap do |output|
+        assert_match "PostTest:FirstFilter", output
+        assert_match "PostTest:SecondFilter", output
+        assert_match "2 runs, 2 assertions", output
+      end
+    end
+
     def test_more_than_one_line_filter_with_multiple_files
       app_file "test/models/account_test.rb", <<-RUBY
         require "test_helper"