[Fix #11188]

Add a `--no-detach` option to `--start-server`. This makes it easy to
run the RuboCop server process from within Docker, where detaching the
process causes the container to exit.

changelog/new_add_no_detach_option.md

@@ -0,0 +1 @@
+* [#11188](https://github.com/rubocop/rubocop/issues/11188): Add a `--no-detach` option for `--start-server`. This will start the server process in the foreground, which can be helpful when running within Docker where detaching the process terminates the container. ([@f1sherman][])

docs/modules/ROOT/pages/usage/server.adoc

@@ -57,6 +57,12 @@ RuboCop version incompatibility found, RuboCop server restarting...
 RuboCop server starting on 127.0.0.1:60665.
 ```
 
+If you would like to start the server in the foreground, which can be useful when running within Docker, you can pass the `--no-detach` option.
+
+```console
+% rubocop --start-server --no-detach
+```
+
 == Restart Server
 
 The started server does not reload the configuration file.
@@ -92,6 +98,9 @@ These are the command-line options for server operations:
 
 | `--server-status`
 | Show server status.
+
+| `--no-detach`
+| Run the server process in the foreground.
 |===
 
 TIP: You can specify the server host and port with the $RUBOCOP_SERVER_HOST and the $RUBOCOP_SERVER_PORT environment variables.

lib/rubocop/options.rb

@@ -206,6 +206,7 @@ def add_server_options(opts)
         option(opts, '--start-server')
         option(opts, '--stop-server')
         option(opts, '--server-status')
+        option(opts, '--no-detach')
       end
     end
 
@@ -465,6 +466,7 @@ def validate_cache_enabled_for_cache_root
 
   # This module contains help texts for command line options.
   # @api private
+  # rubocop:disable Metrics/ModuleLength
   module OptionsHelp
     MAX_EXCL = RuboCop::Options::DEFAULT_MAXIMUM_EXCLUSION_ITEMS.to_s
     FORMATTER_OPTION_LIST = RuboCop::Formatter::FormatterSet::BUILTIN_FORMATTERS_FOR_KEYS.keys
@@ -599,9 +601,11 @@ module OptionsHelp
       start_server:                     'Start server process.',
       stop_server:                      'Stop server process.',
       server_status:                    'Show server status.',
+      no_detach:                        'Run the server process in the foreground.',
       raise_cop_error:                  ['Raise cop-related errors with cause and location.',
                                          'This is used to prevent cops from failing silently.',
                                          'Default is false.']
     }.freeze
   end
+  # rubocop:enable Metrics/ModuleLength
 end

lib/rubocop/server/cli.rb

@@ -23,15 +23,21 @@ class CLI
       STATUS_ERROR = 2
 
       SERVER_OPTIONS = %w[
-        --server --no-server --server-status --restart-server --start-server --stop-server
+        --server
+        --no-server
+        --server-status
+        --restart-server
+        --start-server
+        --stop-server
+        --no-detach
       ].freeze
       EXCLUSIVE_OPTIONS = (SERVER_OPTIONS - %w[--server --no-server]).freeze
+      NO_DETACH_OPTIONS = %w[--server --start-server --restart-server].freeze
 
       def initialize
         @exit = false
       end
 
-      # rubocop:disable Metrics/AbcSize, Metrics/CyclomaticComplexity, Metrics/MethodLength
       def run(argv = ARGV)
         unless Server.support_server?
           return error('RuboCop server is not supported by this Ruby.') if use_server_option?(argv)
@@ -40,48 +46,60 @@ def run(argv = ARGV)
         end
 
         Cache.cache_root_path = fetch_cache_root_path_from(argv)
-        deleted_server_arguments = delete_server_argument_from(argv)
 
-        if deleted_server_arguments.size >= 2
-          return error("#{deleted_server_arguments.join(', ')} cannot be specified together.")
+        process_arguments(argv)
+      end
+
+      def exit?
+        @exit
+      end
+
+      private
+
+      # rubocop:disable Metrics/AbcSize, Metrics/CyclomaticComplexity, Metrics/MethodLength
+      def process_arguments(argv)
+        server_arguments = delete_server_argument_from(argv)
+
+        detach = !server_arguments.delete('--no-detach')
+
+        if server_arguments.size >= 2
+          return error("#{server_arguments.join(', ')} cannot be specified together.")
         end
 
-        server_command = deleted_server_arguments.first
+        server_command = server_arguments.first
+
+        unless detach || NO_DETACH_OPTIONS.include?(server_command)
+          return error("#{server_command} cannot be combined with --no-detach.")
+        end
 
         if EXCLUSIVE_OPTIONS.include?(server_command) && argv.count > allowed_option_count
-          return error("#{server_command} cannot be combined with other options.")
+          return error("#{server_command} cannot be combined with #{argv[0]}.")
         end
 
         if server_command.nil?
           server_command = ArgumentsEnv.read_as_arguments.delete('--server') ||
                            ArgumentsFile.read_as_arguments.delete('--server')
         end
 
-        run_command(server_command)
+        run_command(server_command, detach: detach)
 
         STATUS_SUCCESS
       end
       # rubocop:enable Metrics/AbcSize, Metrics/CyclomaticComplexity, Metrics/MethodLength
 
-      def exit?
-        @exit
-      end
-
-      private
-
       # rubocop:disable Metrics/CyclomaticComplexity, Metrics/MethodLength:
-      def run_command(server_command)
+      def run_command(server_command, detach:)
         case server_command
         when '--server'
-          Server::ClientCommand::Start.new.run unless Server.running?
+          Server::ClientCommand::Start.new(detach: detach).run unless Server.running?
         when '--no-server'
           Server::ClientCommand::Stop.new.run if Server.running?
         when '--restart-server'
           @exit = true
           Server::ClientCommand::Restart.new.run
         when '--start-server'
           @exit = true
-          Server::ClientCommand::Start.new.run
+          Server::ClientCommand::Start.new(detach: detach).run
         when '--stop-server'
           @exit = true
           Server::ClientCommand::Stop.new.run

lib/rubocop/server/client_command/start.rb

@@ -15,6 +15,11 @@ module ClientCommand
       # This class is a client command to start server process.
       # @api private
       class Start < Base
+        def initialize(detach: true)
+          @detach = detach
+          super()
+        end
+
         def run
           if Server.running?
             warn "RuboCop server (#{Cache.pid_path.read}) is already running."
@@ -34,7 +39,7 @@ def run
             host = ENV.fetch('RUBOCOP_SERVER_HOST', '127.0.0.1')
             port = ENV.fetch('RUBOCOP_SERVER_PORT', 0)
 
-            Server::Core.new.start(host, port)
+            Server::Core.new.start(host, port, detach: @detach)
           end
         end
       end

lib/rubocop/server/core.rb

@@ -27,31 +27,46 @@ def token
         self.class.token
       end
 
-      def start(host, port)
+      def start(host, port, detach: true)
         $PROGRAM_NAME = "rubocop --server #{Cache.project_dir}"
 
         require 'rubocop'
         start_server(host, port)
 
-        demonize if server_mode?
+        return unless server_mode?
+
+        detach ? detach_server : run_server
       end
 
       private
 
-      def demonize
-        Cache.write_port_and_token_files(port: @server.addr[1], token: token)
+      def detach_server
+        write_port_and_token_files
 
         pid = fork do
           Process.daemon(true)
           $stderr.reopen(Cache.stderr_path, 'w')
-          Cache.write_pid_file do
-            read_socket(@server.accept) until @server.closed?
-          end
+          process_input
         end
 
         Process.waitpid(pid)
       end
 
+      def write_port_and_token_files
+        Cache.write_port_and_token_files(port: @server.addr[1], token: token)
+      end
+
+      def process_input
+        Cache.write_pid_file do
+          read_socket(@server.accept) until @server.closed?
+        end
+      end
+
+      def run_server
+        write_port_and_token_files
+        process_input
+      end
+
       def server_mode?
         true
       end

spec/rubocop/options_spec.rb

@@ -98,6 +98,7 @@ def abs(path)
                   --start-server               Start server process.
                   --stop-server                Stop server process.
                   --server-status              Show server status.
+                  --no-detach                  Run the server process in the foreground.
 
           Output Options:
               -f, --format FORMATTER           Choose an output formatter. This option

spec/rubocop/server/cli_spec.rb

@@ -53,6 +53,15 @@
       end
     end
 
+    context 'when using `--start-server` option with `--no-detach`' do
+      it 'returns exit status 0 and display an information message' do
+        expect(cli.run(['--start-server', '--no-detach'])).to eq(0)
+        expect(cli.exit?).to be(true)
+        expect($stdout.string).to match(/RuboCop server starting on/)
+        expect($stderr.string).to eq ''
+      end
+    end
+
     context 'when using `--stop-server` option' do
       it 'returns exit status 0 and display a warning message' do
         expect(cli.run(['--stop-server'])).to eq(0)
@@ -71,6 +80,15 @@
       end
     end
 
+    context 'when using `--restart-server` option with `--no-detach`' do
+      it 'returns exit status 0 and display an information message' do
+        expect(cli.run(['--restart-server', '--no-detach'])).to eq(0)
+        expect(cli.exit?).to be(true)
+        expect($stdout.string).to match(/RuboCop server starting on/)
+        expect($stderr.string).to eq "RuboCop server is not running.\n"
+      end
+    end
+
     context 'when using `--server-status` option' do
       it 'returns exit status 0 and display an information message' do
         expect(cli.run(['--server-status'])).to eq(0)
@@ -156,7 +174,7 @@
         expect(cli.run(['--restart-server', '--format', 'simple'])).to eq(2)
         expect(cli.exit?).to be(true)
         expect($stdout.string).to eq ''
-        expect($stderr.string).to eq "--restart-server cannot be combined with other options.\n"
+        expect($stderr.string).to eq "--restart-server cannot be combined with --format.\n"
       end
     end
 
@@ -165,7 +183,7 @@
         expect(cli.run(['--start-server', '--format', 'simple'])).to eq(2)
         expect(cli.exit?).to be(true)
         expect($stdout.string).to eq ''
-        expect($stderr.string).to eq "--start-server cannot be combined with other options.\n"
+        expect($stderr.string).to eq "--start-server cannot be combined with --format.\n"
       end
     end
 
@@ -174,7 +192,7 @@
         expect(cli.run(['--stop-server', '--format', 'simple'])).to eq(2)
         expect(cli.exit?).to be(true)
         expect($stdout.string).to eq ''
-        expect($stderr.string).to eq "--stop-server cannot be combined with other options.\n"
+        expect($stderr.string).to eq "--stop-server cannot be combined with --format.\n"
       end
     end
 
@@ -183,7 +201,16 @@
         expect(cli.run(['--server-status', '--format', 'simple'])).to eq(2)
         expect(cli.exit?).to be(true)
         expect($stdout.string).to eq ''
-        expect($stderr.string).to eq "--server-status cannot be combined with other options.\n"
+        expect($stderr.string).to eq "--server-status cannot be combined with --format.\n"
+      end
+    end
+
+    context 'when using server option with `--no-detach` option' do
+      it 'returns exit status 2 and display an error message' do
+        expect(cli.run(['--server-status', '--no-detach'])).to eq(2)
+        expect(cli.exit?).to be(true)
+        expect($stdout.string).to eq ''
+        expect($stderr.string).to eq "--server-status cannot be combined with --no-detach.\n"
       end
     end