Upgrade the irb command to use irb:debug integration

This means that user will get an IRB session that has access to the debug
commands too by activating IRB's debug integration automatically:
https://github.com/ruby/irb#debugging-with-irb

debug.gemspec

@@ -27,6 +27,6 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.extensions    = ['ext/debug/extconf.rb']
 
-  spec.add_dependency "irb", ">= 1.5.0" # for binding.irb(show_code: false)
+  spec.add_dependency "irb", ">= 1.8.2" # for irb:debug integration
   spec.add_dependency "reline", ">= 0.3.8"
 end

lib/debug/irb.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+require 'irb'
+
+module DEBUGGER__
+  module IrbPatch
+    def evaluate(line, line_no)
+      SESSION.send(:restart_all_threads)
+      super
+      # This is to communicate with the test framework so it can feed the next input
+      puts "INTERNAL_INFO: {}" if ENV['RUBY_DEBUG_TEST_UI'] == 'terminal'
+    ensure
+      SESSION.send(:stop_all_threads)
+    end
+  end
+
+  class ThreadClient
+    def activate_irb_integration
+      IRB.setup(location, argv: [])
+      workspace = IRB::WorkSpace.new(current_frame&.binding || TOPLEVEL_BINDING)
+      irb = IRB::Irb.new(workspace)
+      IRB.conf[:MAIN_CONTEXT] = irb.context
+      IRB::Debug.setup(irb)
+      IRB::Context.prepend(IrbPatch)
+    end
+  end
+end

lib/debug/thread_client.rb

@@ -1048,13 +1048,8 @@ def wait_next_action_
           when :call
             result = frame_eval(eval_src)
           when :irb
-            require 'irb' # prelude's binding.irb doesn't have show_code option
-            begin
-              result = frame_eval('binding.irb(show_code: false)', binding_location: true)
-            ensure
-              # workaround: https://github.com/ruby/debug/issues/308
-              Reline.prompt_proc = nil if defined? Reline
-            end
+            require_relative "irb"
+            activate_irb_integration
           when :display, :try_display
             failed_results = []
             eval_src.each_with_index{|src, i|

test/console/irb_test.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+require_relative '../support/console_test_case'
+
+module DEBUGGER__
+  class IrbTest < ConsoleTestCase
+    def program
+      <<~RUBY
+      1| a = 1
+      2| b = 2
+      RUBY
+    end
+
+    def test_irb_command_switches_console_to_irb
+      debug_code(program, remote: false) do
+        type 'irb'
+        type '123'
+        assert_line_text 'irb:rdbg(main):002> 123'
+        type 'irb_info'
+        assert_line_text('IRB version:')
+        type 'next'
+        type 'info'
+        assert_line_text([/a = 1/, /b = nil/])
+        type 'q!'
+      end
+    end
+  end
+end

test/support/console_test_case.rb

@@ -217,6 +217,7 @@ def prepare_test_environment(program, test_steps, &block)
       ENV['RUBY_DEBUG_TEST_UI'] = 'terminal'
       ENV['RUBY_DEBUG_NO_RELINE'] = 'true'
       ENV['RUBY_DEBUG_HISTORY_FILE'] = ''
+      ENV['TERM'] = 'dumb'
 
       write_temp_file(strip_line_num(program))
       @scenario = []