1 files changed, 130 insertions, 0 deletions
diff --git a/lib/irb/debug.rb b/lib/irb/debug.rb
new file mode 100644
index 0000000000..1ec2335a8e
--- /dev/null
+++ b/lib/irb/debug.rb
@@ -0,0 +1,130 @@
+# frozen_string_literal: true
+
+module IRB
+  module Debug
+    IRB_DIR = File.expand_path('..', __dir__)
+
+    class << self
+      def insert_debug_break(pre_cmds: nil, do_cmds: nil)
+        options = { oneshot: true, hook_call: false }
+
+        if pre_cmds || do_cmds
+          options[:command] = ['irb', pre_cmds, do_cmds]
+        end
+        if DEBUGGER__::LineBreakpoint.instance_method(:initialize).parameters.include?([:key, :skip_src])
+          options[:skip_src] = true
+        end
+
+        # To make debugger commands like `next` or `continue` work without asking
+        # the user to quit IRB after that, we need to exit IRB first and then hit
+        # a TracePoint on #debug_break.
+        file, lineno = IRB::Irb.instance_method(:debug_break).source_location
+        DEBUGGER__::SESSION.add_line_breakpoint(file, lineno + 1, **options)
+      end
+
+      def setup(irb)
+        # When debug session is not started at all
+        unless defined?(DEBUGGER__::SESSION)
+          begin
+            require "debug/session"
+          rescue LoadError # debug.gem is not written in Gemfile
+            return false unless load_bundled_debug_gem
+          end
+          DEBUGGER__::CONFIG.set_config
+          configure_irb_for_debugger(irb)
+
+          DEBUGGER__.initialize_session{ IRB::Debug::UI.new(irb) }
+        end
+
+        # When debug session was previously started but not by IRB
+        if defined?(DEBUGGER__::SESSION) && !irb.context.with_debugger
+          configure_irb_for_debugger(irb)
+          DEBUGGER__::SESSION.reset_ui(IRB::Debug::UI.new(irb))
+        end
+
+        # Apply patches to debug gem so it skips IRB frames
+        unless DEBUGGER__.respond_to?(:capture_frames_without_irb)
+          DEBUGGER__.singleton_class.send(:alias_method, :capture_frames_without_irb, :capture_frames)
+
+          def DEBUGGER__.capture_frames(*args)
+            frames = capture_frames_without_irb(*args)
+            frames.reject! do |frame|
+              frame.realpath&.start_with?(IRB_DIR) || frame.path == "<internal:prelude>"
+            end
+            frames
+          end
+
+          DEBUGGER__::ThreadClient.prepend(SkipPathHelperForIRB)
+        end
+
+        if !@output_modifier_defined && !DEBUGGER__::CONFIG[:no_hint]
+          irb_output_modifier_proc = Reline.output_modifier_proc
+
+          Reline.output_modifier_proc = proc do |output, complete:|
+            unless output.strip.empty?
+              cmd = output.split(/\s/, 2).first
+
+              if !complete && DEBUGGER__.commands.key?(cmd)
+                output = output.sub(/\n$/, " # debug command\n")
+              end
+            end
+
+            irb_output_modifier_proc.call(output, complete: complete)
+          end
+
+          @output_modifier_defined = true
+        end
+
+        true
+      end
+
+      private
+
+      def configure_irb_for_debugger(irb)
+        require 'irb/debug/ui'
+        IRB.instance_variable_set(:@debugger_irb, irb)
+        irb.context.with_debugger = true
+        irb.context.irb_name += ":rdbg"
+      end
+
+      module SkipPathHelperForIRB
+        def skip_internal_path?(path)
+          # The latter can be removed once https://github.com/ruby/debug/issues/866 is resolved
+          super || path.match?(IRB_DIR) || path.match?('<internal:prelude>')
+        end
+      end
+
+      # This is used when debug.gem is not written in Gemfile. Even if it's not
+      # installed by `bundle install`, debug.gem is installed by default because
+      # it's a bundled gem. This method tries to activate and load that.
+      def load_bundled_debug_gem
+        # Discover latest debug.gem under GEM_PATH
+        debug_gem = Gem.paths.path.flat_map { |path| Dir.glob("#{path}/gems/debug-*") }.select do |path|
+          File.basename(path).match?(/\Adebug-\d+\.\d+\.\d+(\w+)?\z/)
+        end.sort_by do |path|
+          Gem::Version.new(File.basename(path).delete_prefix('debug-'))
+        end.last
+        return false unless debug_gem
+
+        # Discover debug/debug.so under extensions for Ruby 3.2+
+        ext_name = "/debug/debug.#{RbConfig::CONFIG['DLEXT']}"
+        ext_path = Gem.paths.path.flat_map do |path|
+          Dir.glob("#{path}/extensions/**/#{File.basename(debug_gem)}#{ext_name}")
+        end.first
+
+        # Attempt to forcibly load the bundled gem
+        if ext_path
+          $LOAD_PATH << ext_path.delete_suffix(ext_name)
+        end
+        $LOAD_PATH << "#{debug_gem}/lib"
+        begin
+          require "debug/session"
+          puts "Loaded #{File.basename(debug_gem)}"
+          true
+        rescue LoadError
+          false
+        end
+      end
+    end
+  end
+end