refactor(parser): reduce work parsing regexps

[overlookmotel]

#1926 produced a small performance regression because when parsing a regexp, some work is repeated.

Hopefully this PR may reverse it.

Perhaps implementation is a little messy, but posting it now as want to see what Codspeed says.

[codspeed-hq]

CodSpeed Performance Report

Merging #1999 will not alter performance

_{Comparing overlookmotel:parser-regex (efee37e) with main (0a08686)}

Summary

✅ 14 untouched benchmarks

[overlookmotel]

Damn it! This makes no difference whatsoever!

Any idea why performance dropped slightly on #1926? Or was it just noise in the benchmarks?

[Boshen]

Damn it! This makes no difference whatsoever!

Any idea why performance dropped slightly on #1926? Or was it just noise in the benchmarks?

Just noise.

---

I forgot that regex has it's own standalone code path for getting the token, this PR is still good because it removes the weird re-parsing code from parse_regex.

There is no perf different because this is such a minor code path, and probably there's only a few regexes in the benchmark.

[overlookmotel]

Thanks. One question: You said on #1926:

In order to make things work nicely, the lexer will no longer recover
from a invalid regex.

Was that a desired outcome, or a compromise you had to make to get it working?

If the latter, I think the old behavior could now be restored after this PR by changing the breaks back into continues in the 2nd loop in read_regex:

oxc/crates/oxc_parser/src/lexer/mod.rs

Lines 871 to 888 in aa91fde

	while let Some(ch @ ('$' | '_' | 'a'..='z' | 'A'..='Z' | '0'..='9')) = self.peek() {
	self.current.chars.next();
	if !ch.is_ascii_lowercase() {
	self.error(diagnostics::RegExpFlag(ch, self.current_offset()));
	break;
	}
	let flag = if let Ok(flag) = RegExpFlags::try_from(ch) {
	flag
	} else {
	self.error(diagnostics::RegExpFlag(ch, self.current_offset()));
	break;
	};
	if flags.contains(flag) {
	self.error(diagnostics::RegExpFlagTwice(ch, self.current_offset()));
	break;
	}
	flags |= flag;
	}

[Boshen]

Was that a desired outcome, or a compromise you had to make to get it working?

A compromise.

But leaving it as a hard error is also fine, I never had any rules for recoverability 😅