Revert "Remove deprecated `server` argument from the rails server command"

This reverts commit fa791fb8.

Reason: `server` argument was deprecated in Rails 6.0. Ref: #32058.

railties/CHANGELOG.md

@@ -2,10 +2,6 @@
 
     *Rafael Mendonça França*
 
-*   Remove deprecated `server` argument from the rails server command.
-
-    *Rafael Mendonça França*
-
 *   Remove deprecated support to old `config.ru` that use the application class as argument of `run`.
 
     *Rafael Mendonça França*

railties/lib/rails/commands/server/server_command.rb

@@ -98,6 +98,8 @@ class ServerCommand < Base # :nodoc:
       DEFAULT_PORT = 3000
       DEFAULT_PID_PATH = "tmp/pids/server.pid"
 
+      argument :using, optional: true
+
       class_option :port, aliases: "-p", type: :numeric,
         desc: "Runs Rails on the specified port - defaults to 3000.", banner: :port
       class_option :binding, aliases: "-b", type: :string,
@@ -124,6 +126,7 @@ def initialize(args, local_options, *)
         super
 
         @original_options = local_options - %w( --restart )
+        deprecate_positional_rack_server_and_rewrite_to_option(@original_options)
       end
 
       def perform
@@ -141,7 +144,7 @@ def perform
             after_stop_callback = -> { say "Exiting" unless options[:daemon] }
             server.start(after_stop_callback)
           else
-            say rack_server_suggestion(options[:using])
+            say rack_server_suggestion(using)
           end
         end
       end
@@ -150,7 +153,7 @@ def perform
         def server_options
           {
             user_supplied_options: user_supplied_options,
-            server:                options[:using],
+            server:                using,
             log_stdout:            log_to_stdout?,
             Port:                  port,
             Host:                  host,
@@ -259,6 +262,22 @@ def prepare_restart
           FileUtils.rm_f(options[:pid]) if options[:restart]
         end
 
+        def deprecate_positional_rack_server_and_rewrite_to_option(original_options)
+          if using
+            ActiveSupport::Deprecation.warn(<<~MSG)
+              Passing the Rack server name as a regular argument is deprecated
+              and will be removed in the next Rails version. Please, use the -u
+              option instead.
+            MSG
+
+            original_options.concat [ "-u", using ]
+          else
+            # Use positional internally to get around Thor's immutable options.
+            # TODO: Replace `using` occurrences with `options[:using]` after deprecation removal.
+            @using = options[:using]
+          end
+        end
+
         def rack_server_suggestion(server)
           if server.in?(RACK_SERVERS)
             <<~MSG

railties/test/commands/server_test.rb

@@ -38,6 +38,10 @@ def test_using_server_mistype_without_suggestion
     assert_no_match(/Maybe you meant/, output)
   end
 
+  def test_using_positional_argument_deprecation
+    assert_match(/DEPRECATION WARNING/, run_command("tin"))
+  end
+
   def test_using_known_server_that_isnt_in_the_gemfile
     assert_match(/Could not load server "unicorn". Maybe you need to the add it to the Gemfile/, run_command("-u", "unicorn"))
   end