catastrophic backtracking in options-list regex

[asottile]

this regex causes catastrophic backtracking leading to denial-of-service for particularly written files --

vscode-rst/syntaxes/rst.tmLanguage.json

Line 187 in 0de9133

"match": "^((?:-\\w|--[\\w-]+|/\\w+)(?:,? ?[\\w-]+)*)(?: |\\t|$)",

here's a small rst example from cpython:

The decimal module now requires libmpdec-2.5.0. Users of
--with-system-libmpdec should update their system library.

when attempting to match the second line the engine will recurse ~essentially forever (libonig has a boundary case to prevent this and raises an error)

I'm a little unfamiliar with what this is attempting to match -- but converting the second group to an atomic group (?>: seems to make the regex terminate quickly rather than spinning

[trond-snekvik]

Hey, thanks for reporting, and thanks for the fix.

I can confirm that the fix does resolve the issue, but as I was writing a test case for this, I found a few other flaws in the options list regex. I made a PR to fix all issues here: #42.

For reference, the options list entry covers this concept: https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#option-lists