Add "Did you mean?" for unrecognized CLI commands

[jonathanhefner]

This commit improves the error message that is displayed when a user specifies an unrecognized bin/rails command by offering "Did you mean?" suggestions. The suggestions cover all visible commands, and supersede any incomplete (Rake-task-only) suggestions that Rake might display.

Before (example)

$ bin/rails credentails:edit
rails aborted!
Don't know how to build task 'credentails:edit' (See the list of available tasks with `rails --tasks`)

(See full trace by running task with --trace)

$ bin/rails --tasks
...
rails cache_digests:dependencies         # Lookup first-level dependencies for TEMPLATE (like messages/show or comments/_comment.html)
rails cache_digests:nested_dependencies  # Lookup nested dependencies for TEMPLATE (like messages/show or comments/_comment.html)
rails db:create                          # Creates the database from DATABASE_URL or config/database.yml for the current RAILS_ENV (use ...
rails db:drop                            # Drops the database from DATABASE_URL or config/database.yml for the current RAILS_ENV (use db...
...

$ bin/rails credentails -h
# no output

$ bin/rails credentials -h
# no output

$ bin/rails versoin
rails aborted!
Don't know how to build task 'versoin' (See the list of available tasks with `rails --tasks`)
Did you mean?  db:version

(See full trace by running task with --trace)

After (example)

$ bin/rails credentails:edit
Unrecognized command "credentails:edit" (Rails::Command::UnrecognizedCommandError)
Did you mean?  credentials:edit

$ bin/rails credentails -h
Unrecognized command "credentails" (Rails::Command::UnrecognizedCommandError)
Did you mean?  credentials:diff

$ bin/rails credentials -h
Unrecognized command "credentials" (Rails::Command::UnrecognizedCommandError)
Did you mean?  credentials:diff

$ bin/rails versoin
Unrecognized command "versoin" (Rails::Command::UnrecognizedCommandError)
Did you mean?  version

[etiennebarrie]

This causes a warning with a default generated engine plugin. It's also related to #46664 (edit: wrong PR).

$ rails plugin new my_engine --main --full
$ cd my_engine
$ sed -Ei '' -e '/uri|homepage|host/ d' -e 's/TODO: //' *.gemspec # fix gemspec to be able to bundle
$ bin/rails test >/dev/null
/tmp/my_engine/Rakefile:3: warning: already initialized constant APP_RAKEFILE
/tmp/my_engine/Rakefile:3: warning: previous definition of APP_RAKEFILE was here

---

Engine plugins have a curious setup which defines all the dummy app's tasks under the :app namespace:

rails/railties/lib/rails/tasks/engine.rake

Lines 4 to 5 in 779c14b

	namespace :app do
	load APP_RAKEFILE

Since #47210 we check if there's a test:prepare task:

rails/railties/lib/rails/commands/test/test_command.rb

Lines 72 to 76 in 779c14b

	def run_prepare_task
	Rails::Command::RakeCommand.perform("test:prepare", [], {})
	rescue UnrecognizedCommandError => error
	raise unless error.name == "test:prepare"
	end

Even though the exception is rescued, to initialize it we need all the existing commands:

rails/railties/lib/rails/command.rb

Line 43 in 779c14b

super("Unrecognized command #{name.inspect}", name, Command.printing_commands.map(&:first))

which asks RakeCommand its commands, which loads the Rakefile again:

rails/railties/lib/rails/command/actions.rb

Lines 31 to 34 in 779c14b

	def load_tasks
	Rake.application.init("rails")
	Rake.application.load_rakefile
	end

---

I can see multiple ways we can fix this:

• UnrecognizedCommandError could delay finding the candidates until they're needed for displaying the exception (since we rescue the exception we don't need it to be displayed). That doesn't solve the underlying double-loading issue though.
• We could re-visit the idea of loading the dummy app's tasks under the :app namespace, I'm not entirely sure why we did and what the consequences would be. For now, that means we don't run test:prepare in engines even if the dummy app has some dependencies that require it.
• In Command::Actions#load_tasks, in the engine case, we could add a conditional to only load tasks if they don't seem to have been loaded already, maybe simply checking if Rails.application.tasks is not empty.

I think the last one makes the most sense, but we need the metadata since we're filtering the tasks without comments, just doing that would remove the did you mean in that case. I think we could load the metadata in engine.rake, that way we don't lose that information for that specific case.

[jonathanhefner]

@etiennebarrie Thank you for the detailed write up! 😍

I think avoiding the double load (option 3) is probably the best way. To that end, I've submitted #47718, which memoizes the already-loaded tasks before raising UnrecognizedCommandError.