[wp-trac] [WordPress Trac] #17817: do_action/apply_filters/etc. recursion on same filter kills underlying call

[WordPress Trac]

#17817: do_action/apply_filters/etc. recursion on same filter kills underlying call
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 Reporter:  kernfel                              |       Owner:
     Type:  defect (bug)                         |      Status:  reopened
 Priority:  normal                               |   Milestone:  Future
Component:  Plugins                              |  Release
 Severity:  normal                               |     Version:  2.2
 Keywords:  dev-feedback has-unit-tests has-     |  Resolution:
  patch                                          |     Focuses:
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Comment (by leewillis77):

 Great to see this being worked on - I just wasted a good two hours trying
 to work out why a hook wasn't being fired with this as the root cause (Not
 in my code thankfully).

 Good news - the patch here resolves the issue I was having. However - it
 causes issues where there are multiple callbacks registered against a
 hook, and an earlier hook accepts fewer arguments than a subsequent hook,
 e.g.

 {{{
 add_action($tag, array(&$a1, 'action'), 10, 2);
 add_action($tag, array(&$a2, 'action'));
 add_action($tag, array(&$a3, 'action'), 10, 2);
 }}}

 In this situation, the third callback will only receive one argument, not
 two. The revised patch attached resolves this, complete with a test to
 prove it. I cannot for the life of me work out why though - it's as though
 the array_slice is affecting $args (Which it shouldn't).

 In my defense, it's late in the day though ...

 So - this probably needs more work (At least we'd need to verify that
 creating a copy of the args rather than reusing a reference doesn't impact
 on performance (CPU or memory)), but throwing this out for discussion.

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Ticket URL: <https://core.trac.wordpress.org/ticket/17817#comment:72>
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