Improved javascript regex highlight

[RexSkz]

Improve JS regex highlight according to references in https://regexr.com/.

Note: this PR can't recognize capture group because "matching bracket" is not a thing where a pure regex way can do.

[RunDevelopment]

Nice PR. I had something similar in mind, so I will share my own ideas as well.

1. I don't think that this alias-approach for styling is good. The fact that the alias escape doesn't do any coloring in the default themes, doesn't help.
   (I personally prefer the subtle color changes for regexes like in editors like VS Code, but this requires that you change all themes Prism offers, so that might be a little overkill...)

2. Please add highlighting for escapes and character ranges inside of character sets.
   This is where I for example use escapes the most often.

Apart from these two things, I really like it. Keep up the good work ^^

[RunDevelopment]

Regarding the quantifiers:
I think that it's a good idea to keep them separately, but *, + and ? (for optional) are also quantifiers, so we should include them as well.
And when we include those, then maybe we should include ? (for lazy) as well? I'm not really sure, what do you think?

Regarding the escapes:
I still think that we should put anchors and default character classes into their own category, as they are not really escape sequences.

[RexSkz]

I started to think that highlighting regex is not a simple job, maybe I should treat regex as a kind of "pseudo language" rather than just improve highlight for some situations. I'll keep trying.

[RexSkz]

@RunDevelopment

Hi, I have re-written my code according to the reference in https://regexr.com.

In this reference, ? for both optional and lazy are called "quantifier".

Now the code can recognize flag, character set, escape, reference, anchor, quantifier and alternation.

It's a pity that recognizing capture group is not a thing where pure regex way can do, because regex can't be used for matching bracket. VSCode can't do this either, it can be proved from here (the class .mtk6 means normal character):

[RunDevelopment]

@RexSkz

Nice work!
With this, you now support almost the full JS regex syntax!

I do have some suggestions:

1. Run escape before any other pattern matching backslashes.
   This will ensure that you don't accidentally match something which is part of an escape sequence. Just add what you want to match later to the [^ ... ] at the end.
2. Rename regex-charset1 to regex-charset and only let it capture stuff like [^...]. Also rename regex-charset2 to regex-charclass and let it capture ., \d can co.
   This will make it easier to correctly match \d (and co). Right now, \\d is matched as a charset1. Searching for it after the escapes ensures correctness. (This requires that the escapes don't match them.)

Apart from that and the minor things I commented on in the code, this looks pretty good.
Also, using VS Code and RegExr for reference was a good idea.

The only thing that is left to do now is to highlight the stuff that is inside of char sets and that's it.

[RexSkz]

@RunDevelopment

Run escape first will seperate the regex (for example [a\\b\\c] will be seperated to [a, b and c]), so that \\b\\ won't be wrapped in charset.

Highlighting stuff inside the character set was not taken into consideration at first, but if it's necessary, using inside (and extra patterns) is a way. The problem is: what should I name the pattern like a-z or the ^ right after [?

Other suggestions seems great, I'll make changes to my code tomorrow, it's midnight here now :(

[RunDevelopment]

@RexSkz

You are absolutely right. charset has to be run before escape. (I forgot to mention it...)

Don't worry, take your time ^^

[RexSkz]

@RunDevelopment

I have pushed another commit, which fixes the bugs and provides more test cases. The most important thing is: it can recognize stuff inside charset now!

[RunDevelopment]

@RexSkz

Looks really good! Well done!

Now, apart from the comments, I have some other things:

1. You used the pattern for escape twice.
   It's quite long. Maybe you could extract it into a variable? (Don't forget to wrap the whole thing with a function block. Just like e.g. Crystal.)
2. Maybe we could highlight the [] of a char set as something like punctuation?
3. Ranges are hard. Do we really need them?
   (Look at my comment for more info)

[RexSkz]

@RunDevelopment

All issues are fixed, range is removed.

[RunDevelopment]

@RexSkz

Looks good!

From a correctness point of view, this PR is ready for merge, but the maintainers might have a thing or two to say about it.

[mAAdhaTTah]

Maybe this should be combined w/ #1714 and put into a js-extras language?

[RunDevelopment]

This is already captured by #1682.

@RexSkz
Thank you for your hard work!