Code Mirror syntax highlighting bugs

[ghost]

As discussed in #3435 (comment), also relevant #3054, the syntax highlighter in Code Mirror has even more severe issues with latex-math and even other things than the basic editor. Here's an example

# Example note

## braces

I don't think this citation to [Some Book, p. 12] should be highlighted, although I also don't really mind it. It shouldn't however happen within latex-math, as it right now does:
$$
	[x].
$$
It even detects within math stuff that is not a link:
$$
	[f+g](x).
$$

## Italics

This works
$$
	x_k = a
$$
so does (with respect to syntax highlighting) this
$$
	x_k_y = incorrect LaTeX code,
$$
(not even rendere by KaTeX), but this correct latex code
$$
	{x_k}_y = THIS  NOT BE HIGHLIGHTED IN ITALICS.
$$
fails the highlighter. It italics even flows out of the math environment.

Can you just please add a detector (and a specific highlighting colour) for math blocks?

[laurent22]

@CalebJohn, do you think it's possible to add a special rule for Katex blocks, so that they are either highlighted as Katex, or highlighting is disabled within the block?

Ace Editor handles this as expected:

Also [Some Book, p. 12] indeed shouldn't be highlighted because it's not a complete Markdown link.

[ghost]

I just noticed that also TV:three_letters_or_more is underlined. Why? the TV: bit is critical, other combinations like AB: don't trigger the underlining.

[CalebJohn]

@yadayadaydadaa Thanks for reporting these issues. Personally I disagree that katex is more broken than in the old editor (although your note does seem to be more broken!) I would say that it is just as broken :). Looking at @laurent22 's screenshot the old editor seems to fail in all the same locations (except the last one where it still fails but differently), but the highlighting is more subtle. I digress. This can be fixed as suggested by @laurent22 . I'll start looking into it right away.

In regards to the TV:three_letters_or_more this was an un-needed highlighting feature, which I'm not sure the purpose of. I disabled it in #3448.

And for [Some Book, p. 12] according to the commonmark spec this is a valid markdown link (which is supported by the Joplin renderer). I suspect this isn't a commonly used feature, so I added a commit to #3448 that disables highlighting for link text. There is still a css class associated with text in a square bracket, so users can turn highlighting back on by adding the .cm-link-text class to userchrome.css.

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