Parse nth-child(-/*comment*/n+b)

[Manishearth]

fixes #153

r? @emilio

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This change is 

[emilio]

I'm a bit confused, the patch in bug 1364009 reads:

Don't allow comments/spaces between signs,numbers,and `n` in an+b syntax for nth-child;

But it seems it's allowing comments but not spaces, right?

[emilio]

nit: spacing.

But I'd write it as:

Token::Delim(delim) => {
    let val = match delim {
        '+' => 1,
        '-' => -1,
        _ => return Err(()),
    };
    match try!(input.next_including_whitespace()) {
        // ...
    }
}

That way you avoid the extra variable at the top too.

[Manishearth]

Yeah, so the spec is weird here. It explicitly includes a specification for all kinds of tokens, including tokens like 3n- (which is a dimension token). Based on these, neither whitespace nor comments are allowed within any token, as is usual. The 3n is never parsed as two tokens, so it never has whitespace. This was the main point of the patch.

On top of that, the -n is parsed as two tokens, but does not allow whitespace, as is specced. Chrome takes this to mean "comments but not whitespace", and Firefox supported comments and whitespace already. So I changed it to be uniformly "comments but not whitespace" everywhere, since by default you can assume that the spec is ignoring comments all the time.

Yes, that probably could be clarified more in that commit message but it's long :) I will try.

In this cssparser PR, i don't really change much behavior, I just make -n behave the the same as +n, which should match up regardless of your interpretation of the rest.

[emilio]

Ok, fair enough.

The fix seems legit (feels weird to treat + differently than - here), and as long as it matches other browsers...

r=me

[emilio]

Let's wait until the discussion in #153 settles though.

[Manishearth]

w3c/csswg-drafts#1498

[SimonSapin]

r=me if w3c/csswg-drafts#1498 is accepted. (I’m officially co-editor of that spec so I could accept that change, but this section is tricky and Tab wrote it so I’d rather have him do it.)

[tabatkins]

👎, this appears to be a total misreading of the Syntax spec. More details in w3c/csswg-drafts#1498

[Manishearth]

This means that these tests only require Firefox fixes to pass now.