[WIP] Implement exit_program (!!!) command

Pry includes an `exit-program` command, also aliased as `quit-program`
and `!!!` which calls `Kernel.exit`. This is useful when `binding.pry`
has been used in a loop.

This implements a similar `exit_program` command, also aliased as
`quit_program` and `!!!`.

lib/irb/cmd/exit_program.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require_relative "nop"
+
+module IRB
+  module ExtendCommand
+    class ExitProgram < Nop
+      category "Misc"
+      description "End the current program, optionally with a status to give to `Kernel.exit`"
+
+      def execute(arg = true)
+        Kernel.exit(arg)
+      end
+    end
+  end
+end

lib/irb/extend-command.rb

@@ -197,6 +197,12 @@ def irb_context
         :irb_history, :History, "cmd/history",
         [:history, NO_OVERRIDE],
         [:hist, NO_OVERRIDE],
+      ],
+
+      [
+        :irb_exit_program, :ExitProgram, 'cmd/exit_program',
+        [:exit_program, NO_OVERRIDE],
+        [:quit_program, NO_OVERRIDE],
       ]
     ]
 

lib/irb/init.rb

@@ -187,8 +187,9 @@ def IRB.init_config(ap_path)
 
     @CONF[:COMMAND_ALIASES] = {
       # Symbol aliases
-      :'$' => :show_source,
-      :'@' => :whereami,
+      :'$'   => :show_source,
+      :'@'   => :whereami,
+      :'!!!' => :exit_program,
     }
   end
 

test/irb/cmd/test_exit_program.rb

@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+require 'irb'
+
+require_relative "../helper"
+
+module TestIRB
+  class ExitProgramTest < IntegrationTestCase
+    def test_irb_exit_program
+      assert_exits_program(with_status: 0) do
+        type "irb_exit_program"
+      end
+    end
+
+    def test_exit_program
+      assert_exits_program(with_status: 0) do
+        type "exit_program"
+      end
+    end
+
+    def test_quit_program
+      assert_exits_program(with_status: 0) do
+        type "quit_program"
+      end
+    end
+
+    def test_triple_bang
+      assert_exits_program(with_status: 0) do
+        type "!!!"
+      end
+    end
+
+    def test_exit_code_zero
+      assert_exits_program(with_status: 0) do
+        type "!!! 0"
+      end
+    end
+
+    def test_exit_code_one
+      assert_exits_program(with_status: 1) do
+        type "!!! 1"
+      end
+    end
+
+    def test_exit_code_expression
+      assert_exits_program(with_status: 2) do
+        type "n = 1"
+        type "!!! n + 1"
+      end
+    end
+
+    def test_exit_code_expression
+      assert_exits_program(with_status: 2) do
+        type "n = 1"
+        type "!!! n + 1"
+      end
+    end
+
+    private
+
+    def assert_exits_program(with_status:, &block)
+      write_ruby <<~'RUBY'
+        begin
+          binding.irb
+          puts "Did not raise #{SystemExit}!" # Interpolate so we don't match whereami context
+        rescue SystemExit => e
+          puts "Raised SystemExit with status #{e.status.inspect}"
+        end
+      RUBY
+
+      output = run_ruby_file(&block)
+
+      refute_includes(output, "Did not raise SystemExit!", "AN ERROR MESSAGE")
+      matching_status = output[/(?<=Raised SystemExit with status )(\d+)/]
+      refute_nil matching_status, "Did not find exit status in output: \n#{output}"
+      assert_equal with_status, matching_status.to_i, "Exited with wrong status code"
+    end
+  end
+end