Adds a --silent option to the CLI (puma#2803)

* Adds a --silent option to the CLI

* Fixes silent opt not to silence stderr

* Removes un-used arg variable from CLI opt block handler

lib/puma/cli.rb

@@ -185,6 +185,10 @@ def setup_options
             user_config.restart_command cmd
           end
 
+          o.on "-s", "--silent", "Do not log prompt messages other than errors" do
+            @events = Events.new NullIO.new, $stderr
+          end
+
           o.on "-S", "--state PATH", "Where to store the state details" do |arg|
             user_config.state_path arg
           end

test/test_cli.rb

@@ -475,4 +475,15 @@ def test_environment_rails_env
   ensure
     ENV.delete 'RAILS_ENV'
   end
+
+  def test_silent
+    cli = Puma::CLI.new ['--silent']
+    cli.send(:setup_options)
+
+    events = cli.instance_variable_get(:@events)
+
+    assert_equal events.class, Puma::Events.null.class
+    assert_equal events.stdout.class, Puma::NullIO
+    assert_equal events.stderr, $stderr
+  end
 end