This will no longer be true once we implement at-rules nested inside
style rules, for example:
```css
.foo {
color: yellow;
@media (min-width: 800px) {
color: orange;
}
}
```
For pseudo elements that represent a browser-generated shadow tree
element, such as ::placeholder, we were reparsing their style attribute
in StyleComputer for some reason.
Instead of doing this, just access the already-parsed version via
Element::inline_style().
These are created when a style rule has properties listed after another
rule. For example:
```css
.test {
--a: 1;
--b: 1;
--c: 1;
.thing {
/* ... */
}
/* These are after a rule (.thing) so they're wrapped in a
CSSNestedDeclarations: */
--d: 1;
--e: 1;
--f: 1;
}
```
They're treated like a nested style rule with the exact same selectors
as their containing style rule.
For example, this:
```css
.foo {
color: red;
&:hover {
color: green;
}
}
```
now has the same effect as this:
```css
.foo {
color: red;
}
.foo:hover {
color: green;
}
```
CSSStyleRule now has "absolutized selectors", which are its selectors
with any `&`s resolved. We use these instead of the "real" selectors
when matching them, meaning the style computer doesn't have to know or
care about where the selector appears in the CSS document.
This will be the first step is making better use of system libraries
like fontconfig and CoreText to load system fonts for use by the UI
process and the CSS style computer.
Transitions are currently not implemented for pseudo elements which
causes the transition to be applied to the "real"/"parent" element. When
a transition adjusts width/height on a pseudo element this causes the
real elements layout to break.
As a quick fix we just skip doing transitions when they are against
pseudo elements.
StyleComputer is responsible for assigning animation targets, so we
have to make sure there are no pending style updates before querying
animations of an element.
This change also introduces a version of getAnimations() that does not
check style updates and used by StyleComputer to avoid mutual recursion.
Previously, we set the "needs style update" flag to false at the
beginning of recomputing the style. This meant that if any code within
the cascade set this flag to true, then we would end style computation
thinking the element still needed its style updating. This could occur
when starting a transition, and would make TreeBuilder crash.
By ensuring that we always set the flag to false at the very end of
style computation, this is avoided, along with any similar issues - I
noticed a comment in `Animation::cancel()` which sounds like a
workaround was needed for a similar problem previously.
This is an ad-hoc implementation that resolves the ready() promise once
the document and all fonts collected by the style computer are done
loading. A spec-compliant implementation would include creating a proxy
CSS::FontFace for each @font-face and correctly implementing the
specification steps for font fetching, but we are far from there yet.
This hackish implementation should yield good WPT progress because it
will actually start waiting for the Ahem font to load before capturing
layout measurements. For example, it makes
https://wpt.live/css/css-grid/abspos/positioned-grid-descendants-001.html
go from 0/100 to 36/100 passing subtests.
This is what the spec tells us to do:
The root element’s display type is always blockified,
and its principal box always establishes an independent
formatting context.
Additionally, a display of contents computes to block
on the root element.
Spec link: https://drafts.csswg.org/css-display/#rootFixes#1562
CSS Fonts level 4 renames font-stretch to font-width, with font-stretch
being left as a legacy alias. Unfortunately the other specs have not yet
been updated, so both terms are used in different places.
When a property is a "legacy name alias", any time it is used in CSS or
via the CSSOM its aliased name is used instead.
(See https://drafts.csswg.org/css-cascade-5/#legacy-name-alias)
This means we only care about the alias when parsing a string as a
PropertyID - and we can just return the PropertyID it is an alias for.
No need for a distinct PropertyID for it, and no need for LibWeb to
care about it at all.
Previously, we had a bunch of these properties, which misused our code
for "logical aliases", some of which I've discovered were not even
fully implemented. But with this change, all that code can go away, and
making a legacy alias is just a case of putting it in the JSON. This
also shrinks `StyleProperties` as it doesn't need to contain data for
these aliases, and removes a whole load of `-webkit-*` spam from the
style inspector.
The spec allows us to either treat them as part of the UA origin, or as
its own origin before author styles. This second behaviour turns out to
be what we are currently doing, which is nice!
Funnily enough this was clarified in the spec barely a month after this
original comment was written. :^)
`revert` is supposed to revert to the previous cascade origin, but we
previously had it reverting to the previous layer. To support both,
track them separately during the cascade.
As part of this, we make `set_property_expanding_shorthands()` fall back
to `initial` if it can't find a previous value to revert to. Previously
we would just shrug and do nothing if that happened, which only works
if the value you want to revert to is whatever is currently in `style`.
That's no longer the case, because `revert` should skip over any layer
styles that have been applied since the previous origin.
If we don't recognize a given transition-property value as a known CSS
property (one that we know about, not necessarily an invalid one),
we should not extrapolate the other transition-foo values for it.
Fixes#1480
As useful as they may be to web developers, :has() selectors complicate
the style invalidation process quite a lot.
Let's have StyleComputer keep track of whether they are present at all
in the current set of active style sheets. This will allow us to
implement fast-path optimizations when there are no :has() selectors.
The web server for WPT has a tendency to just disconnect after sending
us a resource. This makes curl think an error occurred, but it's
actually still recoverable and we have the data.
So instead of just bailing, do what we already do for other kinds of
resources and try to parse the data we got. If it works out, great!
It would be nice to solve this in the networking layer instead, but
I'll leave that as an exercise for our future selves.
Instead of throwing all pseudo-element rules in one bucket, let's have
one bucket per pseudo-element.
This means we only run ::before rules for ::before pseudo-elements,
only ::after rules for ::after, etc.
Average style update time on https://tailwindcss.com/ 250ms -> 215ms.
Once we know the final value of the `content` property for a
pseudo-element, we can bail early if the value is `none` or `normal`
(note that `normal` only applies to ::before and ::after).
In those cases, no pseudo-element will be generated, so everything
that follows in StyleComputer would be wasted work.
This noticeably improves performance on many pages, such as
https://tailwindcss.com/ where style updates go from 360ms -> 250ms.
This makes the way we've implemented the CSS `revert` keyword a lot less
expensive.
Until now, we were making a deep copy of all property values at the
start of each cascade origin. (Those are the values that `revert` would
bring us back to if encountered.)
With this patch, the revert property set becomes a shallow copy, and we
only clone the property set if the cascade ends up writing something.
This knocks a 5% profile item down to 1.3% on https://tailwindcss.com
Skia is more permissive when it comes to font loading, compared to our
own OpenType implementation, which it has superseded, parsing an invalid
TTF does not result in an error but rather produces a font that is
incorrectly displayed. This change updates the FontLoader to address
this behavior and to stop attempting to parse a font as a last resort
when format detection has failed.
Fixes regression on x.com when text is not displayed introduced in
a9d5a99568
Instead of only bucketing these by class name, let's also bucket by
tag name and ID.
Reduces the number of selectors evaluated on https://tailwindcss.com/
from 2.9% to 1.9%.
By filtering first, we end up allocating much less vector space
most of the time.
This is mostly helpful in pathological cases where there's a huge number
of rules present, but most of them get rejected early.
By bucketing these seletors by class or ID, we can avoid running them
in more cases.
Before, we were only avoiding them if the context element wasn't a div.
Now we avoid them for any element that doesn't have that specific class
or ID.
This reduces the number of selectors ran on https://vercel.com by a bit
more, from 1.90% to 1.65%.
These are just roundabout ways of writing .foo, so we can still put them
in the rules-by-class bucket and skip running them when the element
doesn't have that class.
Note that :is(.foo .bar) is also bucketed as a class rule, since the
context element must have the `bar` class for the selector to match.
This is a massive speedup on https://vercel.com/ as it cuts the number
of selectors we actually evaluate from 7.0% to 1.9%.
You can now build with STYLE_INVALIDATION_DEBUG and get a debug stream
of reasons why style invalidations are happening and where.
I've rewritten this code many times, so instead of throwing it away once
again, I figured we should at least have it behind a flag.
Before this change, we were cascading custom properties for each layer,
and then replacing any previously cascaded properties for the element
with only the set from this latest layer.
The patch fixes the issue by making each pass of the custom property
cascade add to the same set, and then finally assigning that set of
properties to the element.
