Avoid calling private methods on the main object (#498)

When the main object is frozen, `IRB` wraps a `SimpleDelegator` around it. But because `SimpleDelegator` doesn't delegate private methods, methods like `require_relative` or `const_get` would cause error, which are needed for lazily loading commands. This commit works around this limitation by avoiding those private method calls when setting up command execution.

Author: st0012

lib/irb/extend-command.rb

@@ -259,8 +259,8 @@ def self.def_extend_command(cmd_name, cmd_class, load_file = nil, *aliases)
  kwargs = ", **kwargs" if RUBY_ENGINE == "ruby" && RUBY_VERSION >= "2.7.0"
  line = __LINE__; eval %[
  def #{cmd_name}(*opts#{kwargs}, &b)
- require_relative "#{load_file}"
- arity = ExtendCommand::#{cmd_class}.instance_method(:execute).arity
+ Kernel.require_relative "#{load_file}"
+ arity = ::IRB::ExtendCommand::#{cmd_class}.instance_method(:execute).arity
  args = (1..(arity < 0 ? ~arity : arity)).map {|i| "arg" + i.to_s }
  args << "*opts#{kwargs}" if arity < 0
  args << "&block"
@@ -269,7 +269,7 @@ def #{cmd_name}(*opts#{kwargs}, &b)
  unless singleton_class.class_variable_defined?(:@@#{cmd_name}_)
  singleton_class.class_variable_set(:@@#{cmd_name}_, true)
  def self.#{cmd_name}_(\#{args})
- ExtendCommand::#{cmd_class}.execute(irb_context, \#{args})
+ ::IRB::ExtendCommand::#{cmd_class}.execute(irb_context, \#{args})
  end
  end
  ], nil, __FILE__, line
@@ -279,7 +279,7 @@ def self.#{cmd_name}_(\#{args})
  else
  line = __LINE__; eval %[
  def #{cmd_name}(*opts, &b)
- ExtendCommand::#{cmd_class}.execute(irb_context, *opts, &b)
+ ::IRB::ExtendCommand::#{cmd_class}.execute(irb_context, *opts, &b)
  end
  ], nil, __FILE__, line
  end

test/irb/test_cmd.rb

@@ -49,6 +49,19 @@ def execute_lines(*lines, conf: {}, main: self, irb_path: nil)
  end
  end
 
+ class FrozenObjectTest < CommandTestCase
+ def test_calling_command_on_a_frozen_main
+ main = Object.new.freeze
+
+ out, err = execute_lines(
+ "irb_info",
+ main: main
+ )
+ assert_empty err
+ assert_match(/RUBY_PLATFORM/, out)
+ end
+ end
+
  class CommnadAliasTest < CommandTestCase
  def test_vars_with_aliases
  @foo = "foo"