Bug #11669: inconsitent behavior of refining frozen class

• Status: Closed
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -
• ruby -v: ruby 2.3.0dev (2015-10-26 trunk 52291) [x86_64-darwin15]
• Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
• Tags: refine

[naruse (Yui NARUSE)]

Is this expected behavior?

class C
  def foo
    p 1
  end
end
module Foo
  refine C do
    def foo
      p 2
    end
  end
end
using Foo
C.new.foo #=> 2
C.freeze
module Foo
  refine C do
    def foo
      p 3
    end
    def bar #=>  can't modify frozen class (RuntimeError)
      p 3
    end
  end
end
C.new.foo
C.new.bar

ruby 2.3.0dev (2015-10-26 trunk 52291) [x86_64-darwin15]
2
test.rb:21:in `block in <module:Foo>': can't modify frozen class (RuntimeError)
	from test.rb:17:in `refine'
	from test.rb:17:in `<module:Foo>'
	from test.rb:16:in `<main>'

[jeremyevans0 (Jeremy Evans)]

Here's the backtrace showing why the frozen error is raised:

#0  rb_class_modify_check (klass=7782713867440) at eval.c:495
#1  0x00000713a3570c14 in rb_method_entry_make (klass=7782713867440, mid=51041, defined_class=7782713867440, visi=METHOD_VISI_PUBLIC, type=VM_METHOD_TYPE_REFINED, def=0x0, original_id=51041, opts=0x0)
    at ./vm_method.c:714
#2  0x00000713a356f598 in rb_add_method (klass=7782713867440, mid=51041, type=VM_METHOD_TYPE_REFINED, opts=0x0, visi=METHOD_VISI_PUBLIC) at ./vm_method.c:831
#3  0x00000713a35708f4 in rb_add_refined_method_entry (refined_class=7782713867440, mid=51041) at ./vm_method.c:655
#4  0x00000713a3570c46 in rb_method_entry_make (klass=7782713865520, mid=51041, defined_class=7782713865520, visi=METHOD_VISI_PUBLIC, type=VM_METHOD_TYPE_ISEQ, def=0x0, original_id=51041, opts=0x7f7ffffcb250)
    at ./vm_method.c:718
#5  0x00000713a356f598 in rb_add_method (klass=7782713865520, mid=51041, type=VM_METHOD_TYPE_ISEQ, opts=0x7f7ffffcb250, visi=METHOD_VISI_PUBLIC) at ./vm_method.c:831
#6  0x00000713a3571370 in rb_add_method_iseq (klass=7782713865520, mid=51041, iseq=0x713ed7001b8, cref=0x7140de521f8, visi=METHOD_VISI_PUBLIC) at ./vm_method.c:848
#7  0x00000713a358afa3 in vm_define_method (ec=0x71432617650, obj=8, id=51041, iseqval=7782169313720, is_singleton=0) at ./vm_insnhelper.c:4036
#8  0x00000713a35670cd in vm_exec_core (ec=0x71432617650, initial=0) at insns.def:756
#9  0x00000713a357fc02 in rb_vm_exec (ec=0x71432617650, mjit_enable_p=1) at vm.c:1936
#10 0x00000713a35a6227 in invoke_block (ec=0x71432617650, iseq=0x713ed7003c0, self=7782713865520, captured=0x7f7ffffcd418, cref=0x7140de521f8, type=572653569, opt_pc=0) at vm.c:1052
#11 0x00000713a35a5e32 in invoke_iseq_block_from_c (ec=0x71432617650, captured=0x7f7ffffcd418, self=7782713865520, argc=0, argv=0x0, kw_splat=0, passed_block_handler=0, cref=0x7140de521f8, is_lambda=0, me=0x0)
    at vm.c:1124
#12 invoke_block_from_c_bh (ec=0x71432617650, block_handler=140187732333593, argc=0, argv=0x0, kw_splat=0, passed_block_handler=0, cref=0x7140de521f8, is_lambda=0, force_blockarg=0) at vm.c:1142
#13 0x00000713a357a3d4 in vm_yield_with_cref (ec=0x71432617650, argc=0, argv=0x0, kw_splat=0, cref=0x7140de521f8, is_lambda=0) at vm.c:1179
#14 0x00000713a357a0f8 in rb_yield_refine_block (refinement=7782713865520, refinements=7782713865720) at ./vm_eval.c:1782
#15 0x00000713a32ea0fc in rb_mod_refine (module=7782713866920, klass=7782713867440) at eval.c:1587

Basically, refined methods modify the method table for the class, which isn't allowed if the class is frozen. If these methods are considered internal, it seems reasonable not to raise in this case. I've added a pull request that implements that: https://github.com/ruby/ruby/pull/3175

[ko1 (Koichi Sasada)]

How about to simply prohibit refine on frozen class?

[byroot (Jean Boussier)]

How about to simply prohibit refine on frozen class?

Conceptually that sounds weird. Freezing a class is to prevent it from being mutated, but refinements are supposed to be a way to extend a class for yourself without mutating it.

[matz (Yukihiro Matsumoto)]

Refinement should be able to apply to frozen classes. Go ahead.

Matz.

• Status changed from Assigned to Closed

Applied in changeset git|b6d6b896159390014020caac69fa465029af5460.

---

Allow refining a frozen class

Doing so modifies the class's method table, but not in a way that should
be detectable from Ruby, so it may be safe to avoid checking if the
class is frozen.

Fixes [Bug #11669]