Fix exit! command warning and method behavior (#868)

* Fix exit! command warning and method behavior

* Remove arg(0) from Kernel.exit and Kernel.exit!

lib/irb.rb

@@ -989,7 +989,7 @@ def run(conf = IRB.conf)
         conf[:AT_EXIT].each{|hook| hook.call}
 
         context.io.save_history if save_history
-        Kernel.exit(0) if forced_exit
+        Kernel.exit if forced_exit
       end
     end
 

lib/irb/cmd/force_exit.rb

@@ -13,7 +13,7 @@ class ForceExit < Nop
       def execute(*)
         throw :IRB_EXIT, true
       rescue UncaughtThrowError
-        Kernel.exit(0)
+        Kernel.exit!
       end
     end
   end

lib/irb/workspace.rb

@@ -90,11 +90,11 @@ def initialize(*main)
         IRB.conf[:__MAIN__] = @main
         @main.singleton_class.class_eval do
           private
-          define_method(:exit) do |*a, &b|
-            # Do nothing, will be overridden
-          end
           define_method(:binding, Kernel.instance_method(:binding))
           define_method(:local_variables, Kernel.instance_method(:local_variables))
+          # Define empty method to avoid delegator warning, will be overridden.
+          define_method(:exit) {|*a, &b| }
+          define_method(:exit!) {|*a, &b| }
         end
         @binding = eval("IRB.conf[:__MAIN__].instance_eval('binding', __FILE__, __LINE__)", @binding, *@binding.source_location)
       end

test/irb/cmd/test_force_exit.rb

@@ -47,5 +47,17 @@ def foo
 
       assert_match(/irb\(main\):001> 123/, output)
     end
+
+    def test_forced_exit_out_of_irb_session
+      write_ruby <<~'ruby'
+        at_exit { puts 'un' + 'reachable' }
+        binding.irb
+        exit! # this will call exit! method overrided by command
+      ruby
+      output = run_ruby_file do
+        type "exit"
+      end
+      assert_not_include(output, 'unreachable')
+    end
   end
 end

test/irb/test_cmd.rb

@@ -58,9 +58,7 @@ def test_calling_command_on_a_frozen_main
         "irb_info",
         main: main
       )
-      # Because the main object is frozen, IRB would wrap a delegator around it
-      # Which's exit! method can't be overridden and would raise a warning
-      assert_match(/delegator does not forward private method #exit\!/, err)
+      assert_empty(err)
       assert_match(/RUBY_PLATFORM/, out)
     end
   end