bug#60054: 29.0.60; Infinite loop when there are cyclic path in the parse tree

[Yuan Fu]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Yuan Fu <casouri@gmail.com>
>> Date: Wed, 14 Dec 2022 12:27:58 -0800
>> Cc: 60054@debbugs.gnu.org
>> 
>> >> https://github.com/tree-sitter/tree-sitter-c/issues/119
>> >> 
>> >> So far, I’ve only observed this in that specific edge case.
>> > 
>> > We should have protection against that, which should be easy, right?
>> 
>> Just to make sure, we want to use something like slow-fast pointers,
>> where we have two pointers, and one goes twice as fast, right?
>> That’s the one I was taught in school :-)
>
> No, I mean protect us from inflooping by checking that the parent of a
> node is not the node itself.

In this particular case, it is the siblings’ parent that equals to the
node. Ie, node->sibling->parent = node.  If your intention is to protect
us from this particular case, switching to use cursors will avoid this
bug.

Yuan