Method peek

crates/css_parse/src/syntax/declaration.rs:79–119

(p: &Parser<'a, Iter>, c: Cursor)

	#[inline(always)]
	fn peek<Iter>(p: &Parser<'a, Iter>, c: Cursor) -> bool
	where
		Iter: Iterator<Item = crate::Cursor> + Clone,
	{
		// A declaration must be an Ident followed by a Colon (with any number of whitespace inbetween). If that is not the
		// case then it definitely cannot be parsed as a Declaration.
		//
		// https://drafts.csswg.org/css-syntax-3/#consume-a-blocks-contents
		// ... "If the next non-whitespace token isn’t a <colon-token>, you can similarly immediately stop parsing as a
		// declaration." ... "(That is, font+ ... is guaranteed to not be a property"...
		if c != Kind::Ident || p.peek_n(2) != Kind::Colon {
			return false;
		}

		// https://drafts.csswg.org/css-syntax-3/#consume-a-blocks-contents
		// ... "If the first two non-whitespace tokens are a custom property name and a colon, it’s definitely a custom
		// property and won’t ever produce a valid rule" ... "(That is, --foo:hover {...} is guaranteed to be a custom
		// property, not a rule.)".
		if c.token().is_dashed_ident() {
			return true;
		}

		// If the third token is a `Colon` then it's likely a Pseudo Element selector. Colons are not valid value tokens
		// inside of a declaration at current, however this is _technically_ a non-standard affordance that may be removed
		// in future.
		if p.peek_n(3) == Kind::Colon {
			return false;
		}

		// https://drafts.csswg.org/css-syntax-3/#consume-a-blocks-contents
		// ... "If the first three non-whitespace tokens are a valid property name, a colon, and anything other than a
		// <{-token>, and then while parsing the declaration's value you encounter a <{-token>, you can immediately stop
		// parsing as a declaration and reparse as a rule instead.
		// (That is, font:bar {... is guaranteed to be an invalid property.)"
		if p.peek_n(4) == Kind::LeftCurly || p.peek_n(5) == Kind::LeftCurly {
			return false;
		}

		// All early checks have been exhausted, so the next step is to parse the Declaration to see if it is valid.
		true
	}
}

impl<'a, V, M> Parse<'a> for Declaration<'a, V, M>