Bug #7842: An alias of a "prepend"ed method skips the original method when calling super

• Status: Closed
• Assignee: nobu (Nobuyoshi Nakada)
• Target version: 2.1.0
• ruby -v: ruby 2.0.0dev (2013-02-13 trunk 39225) [x86_64-linux]
• Backport: 1.9.3: DONTNEED, 2.0.0: DONE

[mame (Yusuke Endoh)]

Hello,

  module P
    def m; puts "P"; super; end
  end
  class A
    def m; puts "A"; end
  end
  class B < A
    def m; puts "B"; end
    prepend P
    alias m2 m
  end
  B.new.m2
    #=> expected: P, B, A
    #=> actual:   P, A

Is this intentional?
It looks weird to me that calling super of P#m (as m2) skips A#m.

---

Yusuke Endoh [e-mail]

[marcandre (Marc-Andre Lafortune)]

I agree, this can only be a bug.

[nobu (Nobuyoshi Nakada)]

Rather I expect [B, A] in this case.

[mame (Yusuke Endoh)]

Rather I expect [B, A] in this case.

Fine. I just wanted to point out the weird skipping.
(Actually, I expect nothing for such a code :-)

2013/2/14, SASADA Koichi [e-mail]:

(2013/02/14 16:14), nobu (Nobuyoshi Nakada) wrote:

Rather I expect [B, A] in this case.

+1

--
// SASADA Koichi at atdot dot net

--
Yusuke Endoh [e-mail]

[marcandre (Marc-Andre Lafortune)]

nobu (Nobuyoshi Nakada) wrote:

Rather I expect [B, A] in this case.

You do?

There would be no way to safely monkey patch this method without using Prepend! So any 1.9.x library that uses monkey patching like alias_method_chain could be incompatible with prepended classes!

I expect:
B.instance_method(:m) == B.instance_method(:m2) # => true in rc2, false in trunk, should be true
B.new.m2 # => [P, B, A], since they are aliases appart from their name

Here is another bug (even more clear) that might be related:
B.instance_method(:m).owner # => P in rc2 (ok), B in trunk (not ok)
B.instance_method(:m2).owner # => #<B:0x0000010384b418>, should be P

I wish I had time to look at it further.

[matz (Yukihiro Matsumoto)]

I expect:

  module P
    def m; puts "P"; super; end
  end
  class A
    def m; puts "A"; end
  end
  class B < A
    def m; puts "B"; end
    alias m2 m
    prepend P
    alias m3 m
  end
  B.new.m2
    #=> expected: B, A
  B.new.m3
    #=> expected: P, B, A

Matz.

[phluid61 (Matthew Kerwin)]

I'm sorry, but this ticket confuses me. Why does "A" ever get output, if
B#m does not also call super?

[marcandre (Marc-Andre Lafortune)]

phluid61 (Matthew Kerwin) wrote:

I'm sorry, but this ticket confuses me. Why does "A" ever get output, if
B#m does not also call super?

You're right to be confused, there's a missing super in the examples that everyone assumed was there.

So here's the corrected version:

    module P
      def m; puts "P"; super; end
    end
    class A
      def m; puts "A"; end
    end
    class B < A
      def m; puts "B"; super; end
      alias m2 m
      prepend P
      alias m3 m
    end

    B.new.m2 #=> expected: B, A
    B.new.m3 #=> expected: P, B, A

[marcandre (Marc-Andre Lafortune)]

• Category set to core
• Assignee deleted (matz (Yukihiro Matsumoto))

[ko1 (Koichi Sasada)]

• Assignee set to nobu (Nobuyoshi Nakada)
• Target version changed from 2.6 to 2.1.0

marcandre: why you remove assignee?
you mean specification discussion was finished at [ruby-core:52386]#5?
I assume the reason and I assign this ticket nobu, the patch monster.

[marcandre (Marc-Andre Lafortune)]

ko1 (Koichi Sasada) wrote:

marcandre: why you remove assignee?
you mean specification discussion was finished at [ruby-core:52386]#5?
I assume the reason and I assign this ticket nobu, the patch monster.

Exactly.

[nobu (Nobuyoshi Nakada)]

• Status changed from Assigned to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r44175.
Yusuke, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

proc.c, vm_method.c: fix super and alias

• proc.c (method_owner): return the class where alias is defined, not
  the class original method is defined.
• vm_method.c (rb_method_entry_make, rb_alias): store the originally
  defined class in me. [Bug #7993] [Bug #7842] [Bug #9236]
• vm_method.c (rb_method_entry_get_without_cache): cache included
  module but not iclass.

[nobu (Nobuyoshi Nakada)]

• Backport set to 1.9.3: DONTNEED, 2.0.0: REQUIRED

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 1.9.3: DONTNEED, 2.0.0: REQUIRED to 1.9.3: DONTNEED, 2.0.0: DONE

r44175 was already backported to ruby_2_0_0 at r44345.

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

[usa (Usaku NAKAMURA)]

• Related to Bug #11189: alias prepended module added