Different regular expression match result in PHP 7.4.11 and 7.4.12

[ken678]

I'm hoping someone might be able to explain to me why the following code produces different results in PHP 7.4.11 and 7.4.12. This is a simplified version of a real example from a project I'm working on. I can see that 7.4.12 moved to PCRE 10.35 but can't see any obvious reason why the below would behave differently.

<?php

preg_match('/([^\.]|^)\s*a/', "a", $matches);

var_dump($matches);

https://onlinephp.io/c/b56ca

[kicken]

I'm not sure why there is a difference, but swapping the order of your alternatives seems to fix it.

preg_match('/(^|[^\.])\s*a/', "a", $matches);

 

[requinix]

Most of the time, when you find an oddity like this that can't be explained any other way, the answer is going to be a JIT thing: PCRE isn't supposed to, but occasionally does behave in slightly different ways when JIT is on or off.

ini_set("pcre.jit", 0);
preg_match('/([^\.]|^)\s*a/', "a", $matches);

But turning off JIT is not the best answer. Instead, do what kicken did and tweak the expression so it works.

Anyway, that expression really should work even with JIT enabled, so feel free to file a bug report against PCRE2 about it.
https://github.com/PCRE2Project/pcre2/issues

[ken678]

Thank you for the explanation requinix. I will rework the expression but I'm working on legacy code and the expression is significantly more complicated than the above so just hoping not to break anything!