1 files changed, 86 insertions, 0 deletions
diff --git a/lib/irb/command/debug.rb b/lib/irb/command/debug.rb
new file mode 100644
index 0000000000..f9aca0a672
--- /dev/null
+++ b/lib/irb/command/debug.rb
@@ -0,0 +1,86 @@
+require_relative "../debug"
+
+module IRB
+  # :stopdoc:
+
+  module Command
+    class Debug < Base
+      category "Debugging"
+      description "Start the debugger of debug.gem."
+
+      BINDING_IRB_FRAME_REGEXPS = [
+        '<internal:prelude>',
+        binding.method(:irb).source_location.first,
+      ].map { |file| /\A#{Regexp.escape(file)}:\d+:in (`|'Binding#)irb'\z/ }
+
+      def execute(_arg)
+        execute_debug_command
+      end
+
+      def execute_debug_command(pre_cmds: nil, do_cmds: nil)
+        pre_cmds = pre_cmds&.rstrip
+        do_cmds = do_cmds&.rstrip
+
+        if irb_context.with_debugger
+          # If IRB is already running with a debug session, throw the command and IRB.debug_readline will pass it to the debugger.
+          if cmd = pre_cmds || do_cmds
+            throw :IRB_EXIT, cmd
+          else
+            puts "IRB is already running with a debug session."
+            return
+          end
+        else
+          # If IRB is not running with a debug session yet, then:
+          # 1. Check if the debugging command is run from a `binding.irb` call.
+          # 2. If so, try setting up the debug gem.
+          # 3. Insert a debug breakpoint at `Irb#debug_break` with the intended command.
+          # 4. Exit the current Irb#run call via `throw :IRB_EXIT`.
+          # 5. `Irb#debug_break` will be called and trigger the breakpoint, which will run the intended command.
+          unless binding_irb?
+            puts "Debugging commands are only available when IRB is started with binding.irb"
+            return
+          end
+
+          if IRB.respond_to?(:JobManager)
+            warn "Can't start the debugger when IRB is running in a multi-IRB session."
+            return
+          end
+
+          unless IRB::Debug.setup(irb_context.irb)
+            puts <<~MSG
+              You need to install the debug gem before using this command.
+              If you use `bundle exec`, please add `gem "debug"` into your Gemfile.
+            MSG
+            return
+          end
+
+          IRB::Debug.insert_debug_break(pre_cmds: pre_cmds, do_cmds: do_cmds)
+
+          # exit current Irb#run call
+          throw :IRB_EXIT
+        end
+      end
+
+      private
+
+      def binding_irb?
+        caller.any? do |frame|
+          BINDING_IRB_FRAME_REGEXPS.any? do |regexp|
+            frame.match?(regexp)
+          end
+        end
+      end
+    end
+
+    class DebugCommand < Debug
+      def self.category
+        "Debugging"
+      end
+
+      def self.description
+        command_name = self.name.split("::").last.downcase
+        "Start the debugger of debug.gem and run its `#{command_name}` command."
+      end
+    end
+  end
+end