The :host family of pseudo class selectors select the shadow host
element when matching against a rule from within the element's shadow
tree.
This is a bit convoluted due to the fact that the document-level
StyleComputer keeps track of *all* style rules, and not just the
document-level ones.
In the future, we should refactor style storage so that shadow roots
have their own style scope, and we can simplify a lot of this.
If we determine that a selector is simple enough, we now run it using a
special matching loop that traverses up the DOM ancestor chain without
recursion.
The criteria for this fast path are:
- All combinators involved must be either descendant or child.
- Only tag name, class, ID and attribute selectors allowed.
It's definitely possible to increase the coverage of this fast path,
but this first version already provides a substantial reduction in time
spent evaluating selectors.
48% of the selectors evaluated when loading our GitHub repo are now
using this fast path.
18% speed-up on the "Descendant and child combinators" subtest of
StyleBench. :^)
No functional impact intended. This is just a more complicated way of
writing what we have now.
The goal of this commit is so that we are able to store the 'name' of a
pseudo element for use in serializing 'unknown -webkit-
pseudo-elements', see:
https://www.w3.org/TR/selectors-4/#compat
This is quite awkward, as in pretty much all cases just the selector
type enum is enough, but we will need to cache the name for serializing
these unknown selectors. I can't figure out any reason why we would need
this name anywhere else in the engine, so pretty much everywhere is
still just passing around this raw enum. But this change will allow us
to easily store the name inside of this new struct for when it is needed
for serialization, once those webkit unknown elements are supported by
our engine.
Since each selector can only have zero or one pseudo-element, we match
against it as a separate step, before matching the rest of the
selector. This should be faster, but mostly I did this because I could
not figure out how else to stop selectors without a pseudo-element from
matching the pseudo-element, eg so `.foo` styles don't affect
`.foo::before`.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
