[ruby/irb] Move main object's safe call logic to Context

(https://github.com/ruby/irb/pull/1034)

https://github.com/ruby/irb/commit/9750fa23cc

lib/irb.rb

@@ -1463,21 +1463,16 @@ module IRB
       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 $2
         when "N"
           @context.irb_name
         when "m"
-          main_str = basic_object_safe_main_call(:to_s) rescue "!#{$!.class}"
+          main_str = @context.safe_method_call_on_main(:to_s) rescue "!#{$!.class}"
           truncate_prompt_main(main_str)
         when "M"
-          main_str = basic_object_safe_main_call(:inspect) rescue "!#{$!.class}"
+          main_str = @context.safe_method_call_on_main(:inspect) rescue "!#{$!.class}"
           truncate_prompt_main(main_str)
         when "l"
           ltype

lib/irb/context.rb

@@ -704,5 +704,10 @@ module IRB
     def local_variables # :nodoc:
       workspace.binding.local_variables
     end
+
+    def safe_method_call_on_main(method_name)
+      main_object = main
+      Object === main_object ? main_object.__send__(method_name) : Object.instance_method(method_name).bind_call(main_object)
+    end
   end
 end