Introduce explicit rails server handler option

I mistype `rails server production` instead of `rails server -e
production` expecting to lunch a server in the production environment
all the time. However, the signature of `rails server --help` is:

```
Usage:
  rails server [puma, thin etc] [options]
```

This means that the `production` argument is being interpreted as a Rack
server handler like Puma, Thin or Unicorn.

Should we argue for the `rails server production`? I'm not sure of the
reasons, but the `rails console production` behavior was deprecated in:
https://github.com/rails/rails/pull/29358, so parity with the existing
`rails console production` usage may not hold anymore.

In any case, this PR introduces an explicit option for the Rack servers
configuration. The option is called `--using` (or `-u` for short) to
avoid the `rails server --server` tantrum.

The new interface of `rails server` is:

```
Usage:
  rails server [using] [options]

Options:
  -p, [--port=port]                        # Runs Rails on the specified port - defaults to 3000.
  -b, [--binding=IP]                       # Binds Rails to the specified IP - defaults to 'localhost' in development and '0.0.0.0' in other environments'.
  -c, [--config=file]                      # Uses a custom rackup configuration.
                                           # Default: config.ru
  -d, [--daemon], [--no-daemon]            # Runs server as a Daemon.
  -e, [--environment=name]                 # Specifies the environment to run this server under (development/test/production).
  -u, [--using=name]                       # Specifies the Rack server used to run the application (thin/puma/webrick).
  -P, [--pid=PID]                          # Specifies the PID file.
                                           # Default: tmp/pids/server.pid
  -C, [--dev-caching], [--no-dev-caching]  # Specifies whether to perform caching in development.
      [--early-hints], [--no-early-hints]  # Enables HTTP/2 early hints.
```

As a bonus, if you mistype the server to use, you'll get an
auto-correction message:

```
$ rails s tin
Could not find handler "tin". Maybe you meant "thin" or "cgi"?
Run `rails server --help` for more options.
```

1 files changed, 29 insertions, 4 deletions

diff --git a/railties/test/commands/server_test.rb b/railties/test/commands/server_test.rb
index 33715ea75f..c84be439e4 100644
--- a/railties/test/commands/server_test.rb
+++ b/railties/test/commands/server_test.rb
@@ -1,15 +1,15 @@
 # frozen_string_literal: true
 
-require "abstract_unit"
+require "isolation/abstract_unit"
 require "env_helpers"
 require "rails/command"
 require "rails/commands/server/server_command"
 
-class Rails::ServerTest < ActiveSupport::TestCase
+class Rails::Command::ServerCommandTest < ActiveSupport::TestCase
   include EnvHelpers
 
   def test_environment_with_server_option
-    args = ["thin", "-e", "production"]
+    args = ["-u", "thin", "-e", "production"]
     options = parse_arguments(args)
     assert_equal "production", options[:environment]
     assert_equal "thin", options[:server]
@@ -22,6 +22,24 @@ class Rails::ServerTest < ActiveSupport::TestCase
     assert_nil options[:server]
   end
 
+  def test_explicit_using_option
+    args = ["-u", "thin"]
+    options = parse_arguments(args)
+    assert_equal "thin", options[:server]
+  end
+
+  def test_using_server_mistype
+    assert_match(/Could not find server "tin". Maybe you meant "thin" or "cgi"/, run_command("--using", "tin"))
+  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
+
   def test_daemon_with_option
     args = ["-d"]
     options = parse_arguments(args)
@@ -35,7 +53,7 @@ class Rails::ServerTest < ActiveSupport::TestCase
   end
 
   def test_server_option_without_environment
-    args = ["thin"]
+    args = ["-u", "thin"]
     with_rack_env nil do
       with_rails_env nil do
         options = parse_arguments(args)
@@ -222,6 +240,13 @@ class Rails::ServerTest < ActiveSupport::TestCase
   end
 
   private
+    def run_command(*args)
+      build_app
+      rails "server", *args
+    ensure
+      teardown_app
+    end
+
     def parse_arguments(args = [])
       Rails::Command::ServerCommand.new([], args).server_options
     end