Only require irb if console is unconfigured

Previously, irb would be required by the console whether or not another
console was configured. While this is not a huge issue at the moment, it
will become an issue if irb is removed as a default gem (which has been
proposed for Ruby 3.3).

This commit changes the console command to only require irb if it was
not previously configured, preventing potential issues with it not being
included in an application's dependencies.

There is currently an open discussion about whether irb should be added
to generated Gemfiles. This change is beneficial whether or not that PR
is merged:
- if irb is added to Gemfiles, then this change will prevent errors
  running the rails console for apps that use other consoles
- if irb is added to railties dependencies, then this change will
  result in less libraries required for apps that use other consoles

The tests needed to be updated because of the ordering of the assertion
parameters. Since irb is now only required when the command is run, the
constant can not be referenced first.

railties/lib/rails/commands/console/console_command.rb

@@ -1,8 +1,5 @@
 # frozen_string_literal: true
 
-require "irb"
-require "irb/completion"
-
 require "rails/command/environment_argument"
 
 module Rails
@@ -34,14 +31,17 @@ def initialize(app, options = {})
 
       app.load_console
 
-      @console = app.config.console || IRB
+      @console = app.config.console || begin
+        require "irb"
+        require "irb/completion"
 
-      if @console == IRB
         IRB::WorkSpace.prepend(BacktraceCleaner)
 
         if Rails.env.production?
           ENV["IRB_USE_AUTOCOMPLETE"] ||= "false"
         end
+
+        IRB
       end
     end
 

railties/test/commands/console_test.rb

@@ -55,7 +55,7 @@ def test_console_with_environment
 
   def test_console_defaults_to_IRB
     app = build_app(nil)
-    assert_equal IRB, Rails::Console.new(app).console
+    assert_equal "IRB", Rails::Console.new(app).console.name
   end
 
   def test_console_disables_IRB_auto_completion_in_production
@@ -64,7 +64,7 @@ def test_console_disables_IRB_auto_completion_in_production
 
     with_rack_env "production" do
       app = build_app(nil)
-      assert_equal IRB, Rails::Console.new(app).console
+      assert_equal "IRB", Rails::Console.new(app).console.name
       assert_equal "false", ENV["IRB_USE_AUTOCOMPLETE"]
     end
   ensure
@@ -77,7 +77,7 @@ def test_console_accepts_override_on_IRB_auto_completion_flag
 
     with_rack_env "production" do
       app = build_app(nil)
-      assert_equal IRB, Rails::Console.new(app).console
+      assert_equal "IRB", Rails::Console.new(app).console.name
       assert_equal "true", ENV["IRB_USE_AUTOCOMPLETE"]
     end
   ensure
@@ -90,7 +90,7 @@ def test_console_doesnt_disable_IRB_auto_completion_in_non_production
 
     with_rails_env nil do
       app = build_app(nil)
-      assert_equal IRB, Rails::Console.new(app).console
+      assert_equal "IRB", Rails::Console.new(app).console.name
       assert_nil ENV["IRB_USE_AUTOCOMPLETE"]
     end
   ensure