Bug 259536 – Positive look-behind RegExp doesn't match in JSC but does match in V8

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Jarred Sumner]

Reproduction:
```
const print = globalThis.print ?? console.log;
const re =
  /(?<=^v?|\sv?)(?:(?:0|[1-9]\d{0,9}?)\.){2}(?:0|[1-9]\d{0,9})(?:-(?:--+)?(?:0|[1-9]\d*|\d*[a-z]+\d*)){0,100}(?=$| |\+|\.)(?:(?<=-\S+)(?:\.(?:--?|[\da-z-]*[a-z-]\d*|0|[1-9]\d*)){1,100}?)?(?!\.)(?:\+(?:[\da-z]\.?-?){1,100}?(?!\w))?(?!\+)/;
const res = re.exec("v1.0.1448");
print(res);
```

`res` is null in jsc shell

In Node, `res` is:

```
[ '1.0.1448', index: 1, input: 'v1.0.1448', groups: undefined ]
```

This is running on a build of JSC from July 23rd

[Radar WebKit Bug Importer]

<rdar://problem/112952197>

[Michael Saboff]

Pull request: https://github.com/WebKit/WebKit/pull/16694

[EWS]

Committed 266912@main (caa31552bab4): <https://commits.webkit.org/266912@main>

Reviewed commits have been landed. Closing PR #16694 and removing active labels.