Inexplicable error -8 while matching certain pattern

[michaeltyson]

Hi!

There is an error when matching the following pattern:

a(.|\s)*?asdf

against:

a                b b bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbf

Specifically: a, followed by newline, followed by 16 spaces, followed by b, space, b, space, 35 b's, then an f.

pcregrep 'a(.|\s)*?asdf' returns:

pcregrep: pcre_exec() gave error -8 while matching this text:

a                b b bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbf


pcregrep: Error -8, -21 or -27 means that a resource limit was exceeded.
pcregrep: Check your regex for nested unlimited loops.

Using pcre2 10.37_1, as installed on macOS 11.6 via Homebrew.

Am I missing something obvious? This should work, right?

[zherczeg]

If you using pcre_exec, that means you are using PCRE1, which is not maintained anymore, and it will never see another release. Anyway, the problem is not with pcre1, because PCRE2 also throws PCRE2_ERROR_MATCHLIMIT. This pattern is 2^n exponential pattern on this particular input because both \s and dot matches to space. To avoid long runs, the engine exits at some point.

Because '.|\s' essentially matches to all characters, you can simply enable dotall temporarily for the dot character: a(?s:.)*?asdf.

[michaeltyson]

🤨😄

[zherczeg]

Let me know if you are ok with this answer because we can close this bug then.

[michaeltyson]

I suspect that's more in your court - this still feels like incorrect behaviour to me, but I don't think it's my place 😊

And I'm fine with the workaround.

Thanks!

[zherczeg]

Regex101 says: https://regex101.com/r/6XKrAV/1
Catastrophic backtracking has been detected and the execution of your expression has been halted. To find out more and what this is, please read the following article: Runaway Regular Expressions

Writing good patterns is important, the engine has limits to help you. E.g. a bubble sort is always much slower than a quick sort, whatever a C compiler does, and this is not the fault of the compiler.