Bug #10969: public_send in combination with method_missing raises NameError instead of NoMethodError

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.2.1p85 (2015-02-26 revision 49769) [x86_64-darwin14]
• Backport: 2.0.0: DONTNEED, 2.1: DONTNEED, 2.2: DONE

[senny (Yves Senn)]

While working on the Rails project, specifically this issue https://github.com/rails/rails/issues/19297 I discovered that public_send can raise a NameError instead of a NoMethodError.

Following is a minimal reproduction scenario to trigger the bug. A more detailed example can be found in this Gist: https://gist.github.com/senny/9864a138defa322ed807

class Person
  def implicit_assignment
    nope rescue nil
    public_send "nope="
  end

  def method_missing(*args)
    super
  end
end

a = Person.new
a.implicit_assignment
# test.rb:13:in `method_missing': undefined local variable or method `nope=' for #<Person:0x007f91d1052ef8> (NameError)
# 	from test.rb:4:in `public_send'
# 	from test.rb:4:in `implicit_assignment'
# 	from test.rb:24:in `<main>'

What a found out during debugging:

I am not a C programmer and have very little experience in that field. While debugging the issue I could make some observations what's going on.

The error is being raised in raise_method_missing (https://github.com/ruby/ruby/blob/7790f37efdd8dd42a0a43c3206f6afdd43f8e86a/vm_eval.c#L704-L706):

else if (last_call_status & NOEX_VCALL) {
  format = "undefined local variable or method `%s' for %s";
  exc = rb_eNameError;

last_call_status is stored on the current thread (https://github.com/ruby/ruby/blob/7790f37efdd8dd42a0a43c3206f6afdd43f8e86a/vm_eval.c#L655):

The thread struct is modified in vm_call_method_missing (https://github.com/ruby/ruby/blob/7790f37efdd8dd42a0a43c3206f6afdd43f8e86a/vm_insnhelper.c#L1668):

th->method_missing_reason = ci->aux.missing_reason;

Now the problem is, that the call to public_send with the method name containing an = sign, does not modify the thread struct. This means that it still contains the value assigned from the previous call. That's what nope rescue nil in the reproduction is used for. It assigns NOEX_VCALL to that struct.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset r51427.

---

vm_eval.c: set method_missing_reason

• vm_eval.c (send_internal): set method_missing_reason before
  invoking overriding method_missing method so that the default
  method_missing can achieve it properly.
  [ruby-core:68515] [Bug #10969]

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)
• Backport set to 2.0.0: DONTNEED, 2.1: DONTNEED, 2.2: REQUIRED

[senny (Yves Senn)]

Thank you Nobuyoshi Nakada and Koichi Sasada! 💛

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.0.0: DONTNEED, 2.1: DONTNEED, 2.2: REQUIRED to 2.0.0: DONTNEED, 2.1: DONTNEED, 2.2: DONE

Backported into ruby_2_2 branch at r52771.
The MISSING_NOENTRY was introduced at r50743. I replaced MISSING_NOENTRY it to 0 to backport.