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

[Christian Johansson]

Hello

Some context first, since I needed a multi-line regexp matcher that 
could tell the difference of end-of-string vs newline ($ vs \n) in a 
string I replace occurrences of \n with \r in a string.

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

(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·")


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Hälsningar / Best Regards
Christian