Bug #9475: Behavior change with include + super + alias_method between 1.9.x and 2.x

• Status: Closed
• Assignee: nobu (Nobuyoshi Nakada)
• Target version: -
• ruby -v: ruby 2.1.0p0 (2013-12-25 revision 44422) [x86_64-darwin12.0]
• Backport: 1.9.3: DONTNEED, 2.0.0: DONE, 2.1: DONE

[benweint (Ben Weintraub)]

Ruby 2.0 appears to have introduced a subtle behavior change in method resolution that persists in 2.1.0.

The attached test case (also visible online at https://gist.github.com/benweint/8791007) is extracted from an actual application, and while I won't defend the need to do something like this, it is clear that the behavior changed in 2.0. Note that this sounds similar to https://bugs.ruby-lang.org/issues/9236 but is in fact distinct - the test case given in that bug was fixed in Ruby 2.1.

Steps to reproduce:

1. Run the attached testcase on Ruby 1.9.3 note the output
2. Run the attached testcase on Ruby 2.0.0-p353 or 2.1.0-p0, and note the output

Expected results:
While it's certainly not obvious to me what 'should' happen when executing this code, on 1.9.3, it produces this output:

foo from C
foo from B
foo from A  

Actual results:
On 2.0+, I get this instead

foo from C
foo from B
foo from B (again)
foo from B
foo from B (again)
foo from B
... previous two lines repeated many times ...
test.rb:11: stack level too deep (SystemStackError)

That is to say, on 2.0, we get into an infinitely recursive loop that doesn't happen with 1.9.3.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Assigned
• Assignee set to nobu (Nobuyoshi Nakada)

[nobu (Nobuyoshi Nakada)]

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

Applied in changeset r45367.

---

vm_method.c: fix infinite recursion

• vm_method.c (rb_method_entry_get_without_cache): get rid of
  infinite recursion at aliases in a subclass and a superclass.
  return actually defined class for other than singleton class.
  [ruby-core:60431] [Bug #9475]

[nobu (Nobuyoshi Nakada)]

• Backport changed from 1.9.3: UNKNOWN, 2.0.0: UNKNOWN, 2.1: UNKNOWN to 1.9.3: REQUIRED, 2.0.0: REQUIRED, 2.1: REQUIRED

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)
• Backport changed from 1.9.3: REQUIRED, 2.0.0: REQUIRED, 2.1: REQUIRED to 1.9.3: DONTNEED, 2.0.0: REQUIRED, 2.1: REQUIRED

[nagachika (Tomoyuki Chikanaga)]

• Related to Bug #9663: Segfault with alias_method and include added

[usa (Usaku NAKAMURA)]

• Backport changed from 1.9.3: DONTNEED, 2.0.0: REQUIRED, 2.1: REQUIRED to 1.9.3: DONTNEED, 2.0.0: DONE, 2.1: REQUIRED

backported r45367, r45387, r45388 and r45389 into ruby_2_0_0 at r45750.

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 1.9.3: DONTNEED, 2.0.0: DONE, 2.1: REQUIRED to 1.9.3: DONTNEED, 2.0.0: DONE, 2.1: DONE

r45367, r45387, r45388 and r45389 were backported into ruby_2_1 branch at r45955.