No way to tell if nested block closed by delimiter or EOF

[luniv]

I'm working on parsing media queries, and my understanding is that the syntax specifies that a media feature must end with a ) [1].

For example, if you have the string "(width", Parser::parse_nested_block will return Ok(_). And there is no easy way to determine how if it was closed by a ) or EOF, as far as I can see.

#[test]
fn block_closed_by_delimiter() {
    let mut input = Parser::new("(width");

    assert!(input.expect_parenthesis_block().is_ok());
    let result = input.parse_nested_block(|input| {
        assert!(input.expect_ident_matching("width").is_ok());
        assert!(input.is_exhausted());
        Ok(true)
    });
    assert!(result.is_err());
}

1: http://drafts.csswg.org/mediaqueries/#typedef-media-feature

<media-feature> = ( [ <mf-plain> | <mf-boolean> | <mf-range> ] )

[SimonSapin]

This is by design. The CSS error handling rules say that blocks close implicitly at EOF. (The newer CSS Syntax spec has the same behavior, but is less explicit about it.) This rule is implicit in all other grammar-like syntax definitions, to reduce verbosity.

By the way, you might want to copy some of Servo’s media_queries.rs. Maybe eventually the parsing parts could be move to rust-cssparser.

[luniv]

Ah. Thanks for the information!

I admit the reason I filed this bug was because I was extending the media query support in Servo (kind of got away on me; have pretty much the full spec implemented, just testing it now)