Don't use delegator to install helper methods to main object

IRB used delegator to install command as a method of frozen main object.
Command is not a method now. We can drop it.

lib/irb.rb

@@ -1463,16 +1463,21 @@ def truncate_prompt_main(str) # :nodoc:
       end
     end
 
+    def basic_object_safe_main_call(method)
+      main = @context.main
+      Object === main ? main.__send__(method) : Object.instance_method(method).bind_call(main)
+    end
+
     def format_prompt(format, ltype, indent, line_no) # :nodoc:
       format.gsub(/%([0-9]+)?([a-zA-Z%])/) do
         case $2
         when "N"
           @context.irb_name
         when "m"
-          main_str = @context.main.to_s rescue "!#{$!.class}"
+          main_str = basic_object_safe_main_call(:to_s) rescue "!#{$!.class}"
           truncate_prompt_main(main_str)
         when "M"
-          main_str = @context.main.inspect rescue "!#{$!.class}"
+          main_str = basic_object_safe_main_call(:inspect) rescue "!#{$!.class}"
           truncate_prompt_main(main_str)
         when "l"
           ltype

lib/irb/command/internal_helpers.rb

@@ -19,7 +19,7 @@ def ruby_args(arg)
         # Use throw and catch to handle arg that includes `;`
         # For example: "1, kw: (2; 3); 4" will be parsed to [[1], { kw: 3 }]
         catch(:EXTRACT_RUBY_ARGS) do
-          @irb_context.workspace.binding.eval "IRB::Command.extract_ruby_args #{arg}"
+          @irb_context.workspace.binding.eval "::IRB::Command.extract_ruby_args #{arg}"
         end || [[], {}]
       end
     end

lib/irb/completion.rb

@@ -156,7 +156,8 @@ def eval_global_variables
         end
 
         def eval_class_constants
-          ::Module.instance_method(:constants).bind(eval("self.class")).call
+          klass = ::Object.instance_method(:class).bind_call(receiver)
+          ::Module.instance_method(:constants).bind_call(klass)
         end
       end
     }

lib/irb/workspace.rb

@@ -4,8 +4,6 @@
 #   	by Keiju ISHITSUKA(keiju@ruby-lang.org)
 #
 
-require "delegate"
-
 require_relative "helper_method"
 
 IRB::TOPLEVEL_BINDING = binding
@@ -16,7 +14,7 @@ class WorkSpace
     # set self to main if specified, otherwise
     # inherit main from TOPLEVEL_BINDING.
     def initialize(*main)
-      if main[0].kind_of?(Binding)
+      if Binding === main[0]
         @binding = main.shift
       elsif IRB.conf[:SINGLE_IRB]
         @binding = TOPLEVEL_BINDING
@@ -70,37 +68,16 @@ def initialize(*main)
       unless main.empty?
         case @main
         when Module
-          @binding = eval("IRB.conf[:__MAIN__].module_eval('binding', __FILE__, __LINE__)", @binding, __FILE__, __LINE__)
+          @binding = eval("::IRB.conf[:__MAIN__].module_eval('::Kernel.binding', __FILE__, __LINE__)", @binding, __FILE__, __LINE__)
         else
           begin
-            @binding = eval("IRB.conf[:__MAIN__].instance_eval('binding', __FILE__, __LINE__)", @binding, __FILE__, __LINE__)
+            @binding = eval("::IRB.conf[:__MAIN__].instance_eval('::Kernel.binding', __FILE__, __LINE__)", @binding, __FILE__, __LINE__)
           rescue TypeError
             fail CantChangeBinding, @main.inspect
           end
         end
       end
 
-      case @main
-      when Object
-        use_delegator = @main.frozen?
-      else
-        use_delegator = true
-      end
-
-      if use_delegator
-        @main = SimpleDelegator.new(@main)
-        IRB.conf[:__MAIN__] = @main
-        @main.singleton_class.class_eval do
-          private
-          define_method(:binding, Kernel.instance_method(:binding))
-          define_method(:local_variables, Kernel.instance_method(:local_variables))
-          # Define empty method to avoid delegator warning, will be overridden.
-          define_method(:exit) {|*a, &b| }
-          define_method(:exit!) {|*a, &b| }
-        end
-        @binding = eval("IRB.conf[:__MAIN__].instance_eval('binding', __FILE__, __LINE__)", @binding, *@binding.source_location)
-      end
-
       @binding.local_variable_set(:_, nil)
     end
 
@@ -111,6 +88,9 @@ def initialize(*main)
     attr_reader :main
 
     def load_helper_methods_to_main
+      # Do not load helper methods to frozen objects and BasicObject
+      return unless Object === @main && !@main.frozen?
+
       ancestors = class<<main;ancestors;end
       main.extend ExtendCommandBundle if !ancestors.include?(ExtendCommandBundle)
       main.extend HelpersContainer if !ancestors.include?(HelpersContainer)

test/irb/command/test_cd.rb

@@ -19,6 +19,12 @@ def foo
           end
         end
 
+        class BO < BasicObject
+          def baz
+            "this is baz"
+          end
+        end
+
         binding.irb
       RUBY
     end
@@ -40,6 +46,19 @@ def test_cd
       assert_match(/irb\(Foo\):006>/, out)
     end
 
+    def test_cd_basic_object_or_frozen
+      out = run_ruby_file do
+        type "cd BO.new"
+        type "cd 1"
+        type "cd Object.new.freeze"
+        type "exit"
+      end
+
+      assert_match(/irb\(#<BO:.+\):002>/, out)
+      assert_match(/irb\(1\):003>/, out)
+      assert_match(/irb\(#<Object:.+\):004>/, out)
+    end
+
     def test_cd_moves_top_level_with_no_args
       out = run_ruby_file do
         type "cd Foo"

test/irb/test_context.rb

@@ -652,6 +652,13 @@ def main.inspect; to_s.inspect; end
       assert_equal('irb("aaaaaaaaaaaaaaaaaaaaaaaaaaaa...)>', irb.send(:format_prompt, 'irb(%M)>', nil, 1, 1))
     end
 
+    def test_prompt_main_basic_object
+      main = BasicObject.new
+      irb = IRB::Irb.new(IRB::WorkSpace.new(main), TestInputMethod.new)
+      assert_match(/irb\(#<BasicObject:.+\)/, irb.send(:format_prompt, 'irb(%m)>', nil, 1, 1))
+      assert_match(/irb\(#<BasicObject:.+\)/, irb.send(:format_prompt, 'irb(%M)>', nil, 1, 1))
+    end
+
     def test_prompt_main_raise
       main = Object.new
       def main.to_s; raise TypeError; end