Make regex lookahead check more strict

[RedCMD]

Fixes #1024

Regex on new line breaks js/ts highlighter

[sheetalkamat]

Please add testcase which this fixes

[jimmy-zhening-luo]

@RedCMD , bump. Here's an example of valid TypeScript that transpiles to correct JavaScript but fails highlighting in my IDE:

Example

protected url(string: string) {
  const regex = /^(([^:/?#]+):)?(\/\/([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?/u;
  
  // Hereafter, highlighting broken
  const parts = regex.exec(string);
  
  if (parts === null)
    throw new Error("Input unparseable as URL");
  else
    return {
      scheme: parts[2],
      host: parts[4],
      path: parts[5],
      query: parts[7],
      fragment: parts[9],
    };
}

Environment

• TypeScript versions 5.4.5 to 5.6.2 checked
• Targets ES6
• Strictest compiler options
• Is correctly highlighted in VSCode, but fails in my IDE which depends on the latest TypeScript TmLanguage

[RedCMD]

@jimmy-zhening-luo what IDE do you use?
can you send a screenshot?
should prob make a new bug report

[RedCMD]

Before:

After: