Load Rake tasks only once for command suggestions

Follow-up to rails#47208.

`UnrecognizedCommandError` calls `printing_commands` to make "Did you
mean?" suggestions.  `printing_commands` calls `RakeCommand#rake_tasks`,
which loads the Rake tasks if they have not been memoized.  If the tasks
have already been loaded by `RakeCommand#perform` (but not memoized by
`RakeCommand#rake_tasks`), then the tasks will be loaded a second time.
This can cause, for example, constant redefinition warnings if the task
files define constants.

Therefore, this commit memoizes the tasks from `RakeCommand#perform`
before raising `UnrecognizedCommandError`.

railties/lib/rails/commands/rake/rake_command.rb

@@ -18,7 +18,9 @@ def perform(task, args, config)
           Rake.with_application do |rake|
             rake.init("rails", [task, *args])
             rake.load_rakefile
+
             if unrecognized_task = rake.top_level_tasks.find { |task| !rake.lookup(task[/[^\[]+/]) }
+              @rake_tasks = rake.tasks
               raise UnrecognizedCommandError.new(unrecognized_task)
             end
 
@@ -31,24 +33,22 @@ def perform(task, args, config)
 
         private
           def rake_tasks
-            require_rake
-
-            return @rake_tasks if defined?(@rake_tasks)
-
-            require_application!
-
-            Rake::TaskManager.record_task_metadata = true
-            Rake.application.instance_variable_set(:@name, "rails")
-            load_tasks
-            @rake_tasks = Rake.application.tasks.select(&:comment)
+            @rake_tasks ||= begin
+              require_rake
+              require_application!
+              Rake.application.instance_variable_set(:@name, "rails")
+              load_tasks
+              Rake.application.tasks
+            end
           end
 
           def formatted_rake_tasks
-            rake_tasks.map { |t| [ t.name_with_args, t.comment ] }
+            rake_tasks.filter_map { |t| [ t.name_with_args, t.comment ] if t.comment }
           end
 
           def require_rake
             require "rake" # Defer booting Rake until we know it's needed.
+            Rake::TaskManager.record_task_metadata = true # Preserve task comments.
           end
       end
     end

railties/test/command/help_integration_test.rb

@@ -14,6 +14,18 @@ class Rails::Command::HelpIntegrationTest < ActiveSupport::TestCase
     assert_match "Did you mean?  version", output
   end
 
+  test "loads Rake tasks only once on unrecognized command" do
+    app_file "lib/tasks/my_task.rake", <<~RUBY
+      puts "MY_TASK already defined? => \#{!!defined?(MY_TASK)}"
+      MY_TASK = true
+    RUBY
+
+    output = rails "vershen", allow_failure: true
+
+    assert_match "MY_TASK already defined? => false", output
+    assert_no_match "MY_TASK already defined? => true", output
+  end
+
   test "prints help via `X:help` command when running `X` and `X:X` command is not defined" do
     help = rails "dev:help"
     output = rails "dev", allow_failure: true