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style: Add support for the revert-layer keyword

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This patch looks bigger than it is, but it's mostly because
of plumbing.

To implement revert-layer we need not only the cascade origin of the
declaration, but the whole cascade level, plus also the layer order.

In order to do this, encapsulate these two things inside a 32-bit
`CascadePriority` struct and plumb it through the rule tree and so on.
This allows us to remove the packing and unpacking of CascadeLevel,
though I kept the ShadowCascadeOrder limit for now in case we need to
reintroduce it.

Fix `!important` behavior of layers while at it (implementing it in
`CascadeLevel::cmp`, spec quote included since it was tricky to find)
since some revert-layer tests were depending on it.

The style attribute test is failing now, but follow-up commit fixes
it, see spec issue.

In terms of the actual keyword implementation, it's sort of
straight-forward: We implement revert and revert-layer in a shared
way, by storing the cascade priority that reverted it.

Differential Revision: https://phabricator.services.mozilla.com/D133372
This commit is contained in:
Emilio Cobos Álvarez 2023-06-06 16:49:13 +02:00 • committed by Oriol Brufau
parent 26c10339e3
commit 8bb7d98f0c
17 changed files with 354 additions and 251 deletions
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118
components/style/rule_tree/level.rs
View file

@ -29,7 +29,7 @@ use crate::stylesheets::Origin;
/// [3]: https://html.spec.whatwg.org/multipage/#presentational-hints
/// [4]: https://drafts.csswg.org/css-scoping/#shadow-cascading
#[repr(u8)]
#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, PartialEq, PartialOrd)]
#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Ord, PartialEq, PartialOrd)]
pub enum CascadeLevel {
/// Normal User-Agent rules.
UANormal,
@ -69,82 +69,44 @@ pub enum CascadeLevel {
}
impl CascadeLevel {
/// Pack this cascade level in a single byte.
///
/// We have 10 levels, which we can represent with 4 bits, and then a
/// cascade order optionally, which we can clamp to three bits max, and
/// represent with a fourth bit for the sign.
///
/// So this creates: SOOODDDD
///
/// Where `S` is the sign of the order (one if negative, 0 otherwise), `O`
/// is the absolute value of the order, and `D`s are the discriminant.
#[inline]
pub fn to_byte_lossy(&self) -> u8 {
let (discriminant, order) = match *self {
Self::UANormal => (0, 0),
Self::UserNormal => (1, 0),
Self::PresHints => (2, 0),
/// Convert this level from "unimportant" to "important".
pub fn important(&self) -> Self {
match *self {
Self::UANormal => Self::UAImportant,
Self::UserNormal => Self::UserImportant,
Self::AuthorNormal {
shadow_cascade_order,
} => (3, shadow_cascade_order.0),
Self::SMILOverride => (4, 0),
Self::Animations => (5, 0),
Self::AuthorImportant {
shadow_cascade_order,
} => (6, shadow_cascade_order.0),
Self::UserImportant => (7, 0),
Self::UAImportant => (8, 0),
Self::Transitions => (9, 0),
};
debug_assert_eq!(discriminant & 0xf, discriminant);
if order == 0 {
return discriminant;
} => Self::AuthorImportant {
shadow_cascade_order: -shadow_cascade_order,
},
Self::PresHints |
Self::SMILOverride |
Self::Animations |
Self::AuthorImportant { .. } |
Self::UserImportant |
Self::UAImportant |
Self::Transitions => *self,
}
let negative = order < 0;
let value = std::cmp::min(order.abs() as u8, 0b111);
(negative as u8) << 7 | value << 4 | discriminant
}
/// Convert back from the single-byte representation of the cascade level
/// explained above.
#[inline]
pub fn from_byte(b: u8) -> Self {
let order = {
let abs = ((b & 0b01110000) >> 4) as i8;
let negative = b & 0b10000000 != 0;
if negative {
-abs
} else {
abs
}
};
let discriminant = b & 0xf;
let level = match discriminant {
0 => Self::UANormal,
1 => Self::UserNormal,
2 => Self::PresHints,
3 => {
return Self::AuthorNormal {
shadow_cascade_order: ShadowCascadeOrder(order),
}
/// Convert this level from "important" to "non-important".
pub fn unimportant(&self) -> Self {
match *self {
Self::UAImportant => Self::UANormal,
Self::UserImportant => Self::UserNormal,
Self::AuthorImportant {
shadow_cascade_order,
} => Self::AuthorNormal {
shadow_cascade_order: -shadow_cascade_order,
},
4 => Self::SMILOverride,
5 => Self::Animations,
6 => {
return Self::AuthorImportant {
shadow_cascade_order: ShadowCascadeOrder(order),
}
},
7 => Self::UserImportant,
8 => Self::UAImportant,
9 => Self::Transitions,
_ => unreachable!("Didn't expect {} as a discriminant", discriminant),
};
debug_assert_eq!(order, 0, "Didn't expect an order value for {:?}", level);
level
Self::PresHints |
Self::SMILOverride |
Self::Animations |
Self::AuthorNormal { .. } |
Self::UserNormal |
Self::UANormal |
Self::Transitions => *self,
}
}
/// Select a lock guard for this level
@ -231,6 +193,12 @@ impl CascadeLevel {
pub struct ShadowCascadeOrder(i8);
impl ShadowCascadeOrder {
/// We keep a maximum of 3 bits of order as a limit so that we can pack
/// CascadeLevel in one byte by using half of it for the order, if that ends
/// up being necessary.
const MAX: i8 = 0b111;
const MIN: i8 = -Self::MAX;
/// A level for the outermost shadow tree (the shadow tree we own, and the
/// ones from the slots we're slotted in).
#[inline]
@ -256,7 +224,9 @@ impl ShadowCascadeOrder {
#[inline]
pub fn dec(&mut self) {
debug_assert!(self.0 < 0);
self.0 = self.0.saturating_sub(1);
if self.0 != Self::MIN {
self.0 -= 1;
}
}
/// The level, moving inwards. We should only move inwards if we're
@ -264,7 +234,9 @@ impl ShadowCascadeOrder {
#[inline]
pub fn inc(&mut self) {
debug_assert_ne!(self.0, -1);
self.0 = self.0.saturating_add(1);
if self.0 != Self::MAX {
self.0 += 1;
}
}
}