bug#53680: Endless loop in peculiar case of string-match and string-match-p 27.02 and 28.0.50

[Lars Ingebrigtsen]

Christian Johansson <christian@cvj.se> writes:

> In a peculiar case a endless loop happens and I can reproduce this bug
> in Emacs 27.2 and 28.0.50 (have not tested any other versions), ok try
> to eval following snippet:
>
> (string-match-p·"[\r\t·]*implements[\r\t·]+\\([\r\t·]*[\\a-zA-Z_0-9_]+,?\\)+[\r\t·]*{$"·"ariable·implements·\\Magento\\Framework\\Event\\OberserverInterface\r{\r····public·function·__construct()\r·")
> or

I guess the · are supposed to be spaces, so it's:

(string-match
 "[\r\t ]*implements[\r\t ]+\\([\r\t ]*[\\a-zA-Z_0-9_]+,?\\)+[\r\t ]*{$"
 "ariable implements \\Magento\\Framework\\Event\\OberserverInterface\r{\r    
public function __construct()\r ")

And I can reproduce this on master, too.  Is it a problem with excessive
backtracking, perhaps?  I let it run for a minute, and it didn't finish
in that time.

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