Add debug command (#446)

Author: st0012

lib/irb.rb

@@ -393,6 +393,8 @@ def IRB.irb_abort(irb, exception = Abort)
   end
 
   class Irb
+    DIR_NAME = __dir__
+
     ASSIGNMENT_NODE_TYPES = [
       # Local, instance, global, class, constant, instance, and index assignment:
       #   "foo = bar",
@@ -434,6 +436,16 @@ def initialize(workspace = nil, input_method = nil)
       @scanner = RubyLex.new
     end
 
+    def debug_break
+      # it means the debug command is executed
+      if defined?(DEBUGGER__) && DEBUGGER__.respond_to?(:original_capture_frames)
+        # after leaving this initial breakpoint, revert the capture_frames patch
+        DEBUGGER__.singleton_class.send(:alias_method, :capture_frames, :original_capture_frames)
+        # and remove the redundant method
+        DEBUGGER__.singleton_class.send(:undef_method, :original_capture_frames)
+      end
+    end
+
     def run(conf = IRB.conf)
       conf[:IRB_RC].call(context) if conf[:IRB_RC]
       conf[:MAIN_CONTEXT] = context
@@ -931,5 +943,6 @@ def irb(show_code: true)
     binding_irb = IRB::Irb.new(workspace)
     binding_irb.context.irb_path = File.expand_path(source_location[0])
     binding_irb.run(IRB.conf)
+    binding_irb.debug_break
   end
 end

lib/irb/cmd/debug.rb

@@ -0,0 +1,33 @@
+require_relative "nop"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class Debug < Nop
+      def execute(*args)
+        require "debug/session"
+        DEBUGGER__.start(nonstop: true)
+        DEBUGGER__.singleton_class.send(:alias_method, :original_capture_frames, :capture_frames)
+
+        def DEBUGGER__.capture_frames(skip_path_prefix)
+          frames = original_capture_frames(skip_path_prefix)
+          frames.reject! do |frame|
+            frame.realpath&.start_with?(::IRB::Irb::DIR_NAME) || frame.path.match?(/internal:prelude/)
+          end
+          frames
+        end
+
+        file, lineno = IRB::Irb.instance_method(:debug_break).source_location
+        DEBUGGER__::SESSION.add_line_breakpoint(file, lineno + 1, oneshot: true, hook_call: false)
+        # exit current Irb#run call
+        throw :IRB_EXIT
+      rescue LoadError => e
+        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
+      end
+    end
+  end
+end

lib/irb/extend-command.rb

@@ -116,6 +116,10 @@ def irb_context
         [:kill, OVERRIDE_PRIVATE_ONLY],
       ],
 
+      [
+        :irb_debug, :Debug, "cmd/debug",
+        [:debug, NO_OVERRIDE],
+      ],
       [
         :irb_help, :Help, "cmd/help",
         [:help, NO_OVERRIDE],