C and C++: backslash-newline continues comments

[zackw]

In C, C++, Objective-C, and Objective-C++, the official parser specification requires backslash-newline to be removed from the input stream before comments are handled, which means it can extend comments. The most important case of this is

// this line is a comment \
this line is also part of the comment
this line is outside the comment

where both the first and second lines, but not the third, should be highlighted as a comment. Other cases include

/\
/ this line is a comment
this line is outside the comment

and

/\
* this is a block comment *\
/ outside the comment

https://prismjs.com/test.html currently gets all of these wrong. I would forgive you for not bothering to handle the second and third cases.

And of course -newline can also be spelled ??/-newline, but again, I'd forgive you for not bothering with that one.

[mAAdhaTTah]

I suspect this one is going to be tough to get right with a regex.

[zackw]

For the line comments,

/\/(?:|\\\n)\/.*?(?:\\\n.*)*?[^\\]$/m

WFM in casual testing (see https://regex101.com/r/Q1xuiv/2 ). I didn't bother with trigraphs, because I didn't see a good way to do it without negative lookbehind, which JS regexen don't have. But trigraphs come up far less often.

[mAAdhaTTah]

Ok cool, would you be able to open a PR with that change + tests? Thanks!

[zackw]

I'm sorry, I will not have time to do that for at least two months. (Throwing together regexes is easy. Writing tests is hard.)