Add commands to start and use the debugger (#449)

* Seamlessly integrate a few debug commands

* Improve the break command support

* Utilize skip_src option if available

* Add step and delete commands

* Write end-to-end tests for each debugger command

* Add documentation

* Add backtrace, info, catch commands

Author: k0kubun

Gemfile

@@ -11,4 +11,5 @@ group :development do
   gem "stackprof" if is_unix && !is_truffleruby
   gem "test-unit"
   gem "reline", github: "ruby/reline" if ENV["WITH_LATEST_RELINE"] == "true"
+  gem "debug"
 end

README.md

@@ -90,6 +90,8 @@ The following commands are available on IRB.
   * Show the source code around binding.irb again.
 * `debug`
   * Start the debugger of debug.gem.
+* `break`, `delete`, `next`, `step`, `continue`, `finish`, `backtrace`, `info`, `catch`
+  * Start the debugger of debug.gem and run the command on it.
 
 ## Documentation
 

lib/irb.rb

@@ -96,6 +96,8 @@
 #   * Show the source code around binding.irb again.
 # * debug
 #   * Start the debugger of debug.gem.
+# * break, delete, next, step, continue, finish, backtrace, info, catch
+#   * Start the debugger of debug.gem and run the command on it.
 #
 # == Configuration
 #
@@ -470,10 +472,6 @@ class Irb
     def initialize(workspace = nil, input_method = nil)
       @context = Context.new(self, workspace, input_method)
       @context.main.extend ExtendCommandBundle
-      @context.command_aliases.each do |alias_name, cmd_name|
-        next if @context.symbol_alias(alias_name)
-        @context.main.install_alias_method(alias_name, cmd_name)
-      end
       @signal_status = :IN_IRB
       @scanner = RubyLex.new
     end

lib/irb/cmd/backtrace.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require_relative "debug"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class Backtrace < Debug
+      def self.transform_args(args)
+        args&.dump
+      end
+
+      def execute(*args)
+        super(pre_cmds: ["backtrace", *args].join(" "))
+      end
+    end
+  end
+
+  # :startdoc:
+end

lib/irb/cmd/break.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require_relative "debug"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class Break < Debug
+      def self.transform_args(args)
+        args&.dump
+      end
+
+      def execute(args = nil)
+        super(pre_cmds: "break #{args}")
+      end
+    end
+  end
+
+  # :startdoc:
+end

lib/irb/cmd/catch.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require_relative "debug"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class Catch < Debug
+      def self.transform_args(args)
+        args&.dump
+      end
+
+      def execute(*args)
+        super(pre_cmds: ["catch", *args].join(" "))
+      end
+    end
+  end
+
+  # :startdoc:
+end

lib/irb/cmd/continue.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require_relative "debug"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class Continue < Debug
+      def execute(*args)
+        super(do_cmds: ["continue", *args].join(" "))
+      end
+    end
+  end
+
+  # :startdoc:
+end

lib/irb/cmd/debug.rb

@@ -11,7 +11,7 @@ class Debug < Nop
       ].map { |file| /\A#{Regexp.escape(file)}:\d+:in `irb'\z/ }
       IRB_DIR = File.expand_path('..', __dir__)
 
-      def execute(*args)
+      def execute(pre_cmds: nil, do_cmds: nil)
         unless binding_irb?
           puts "`debug` command is only available when IRB is started with binding.irb"
           return
@@ -25,11 +25,19 @@ def execute(*args)
           return
         end
 
+        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, oneshot: true, hook_call: false)
+        DEBUGGER__::SESSION.add_line_breakpoint(file, lineno + 1, **options)
         # exit current Irb#run call
         throw :IRB_EXIT
       end

lib/irb/cmd/delete.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require_relative "debug"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class Delete < Debug
+      def execute(*args)
+        super(pre_cmds: ["delete", *args].join(" "))
+      end
+    end
+  end
+
+  # :startdoc:
+end

lib/irb/cmd/finish.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require_relative "debug"
+
+module IRB
+  # :stopdoc:
+
+  module ExtendCommand
+    class Finish < Debug
+      def execute(*args)
+        super(do_cmds: ["finish", *args].join(" "))
+      end
+    end
+  end
+
+  # :startdoc:
+end