1 files changed, 545 insertions, 0 deletions
diff --git a/servo/components/style/data.rs b/servo/components/style/data.rs
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+++ b/servo/components/style/data.rs
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Per-node data used in style calculation.
+
+use crate::computed_value_flags::ComputedValueFlags;
+use crate::context::{SharedStyleContext, StackLimitChecker};
+use crate::dom::TElement;
+use crate::invalidation::element::invalidator::InvalidationResult;
+use crate::invalidation::element::restyle_hints::RestyleHint;
+use crate::properties::ComputedValues;
+use crate::selector_parser::{PseudoElement, RestyleDamage, EAGER_PSEUDO_COUNT};
+use crate::style_resolver::{PrimaryStyle, ResolvedElementStyles, ResolvedStyle};
+#[cfg(feature = "gecko")]
+use malloc_size_of::MallocSizeOfOps;
+use selectors::matching::SelectorCaches;
+use servo_arc::Arc;
+use std::fmt;
+use std::mem;
+use std::ops::{Deref, DerefMut};
+
+bitflags! {
+    /// Various flags stored on ElementData.
+    #[derive(Debug, Default)]
+    pub struct ElementDataFlags: u8 {
+        /// Whether the styles changed for this restyle.
+        const WAS_RESTYLED = 1 << 0;
+        /// Whether the last traversal of this element did not do
+        /// any style computation. This is not true during the initial
+        /// styling pass, nor is it true when we restyle (in which case
+        /// WAS_RESTYLED is set).
+        ///
+        /// This bit always corresponds to the last time the element was
+        /// traversed, so each traversal simply updates it with the appropriate
+        /// value.
+        const TRAVERSED_WITHOUT_STYLING = 1 << 1;
+
+        /// Whether the primary style of this element data was reused from
+        /// another element via a rule node comparison. This allows us to
+        /// differentiate between elements that shared styles because they met
+        /// all the criteria of the style sharing cache, compared to elements
+        /// that reused style structs via rule node identity.
+        ///
+        /// The former gives us stronger transitive guarantees that allows us to
+        /// apply the style sharing cache to cousins.
+        const PRIMARY_STYLE_REUSED_VIA_RULE_NODE = 1 << 2;
+    }
+}
+
+/// A lazily-allocated list of styles for eagerly-cascaded pseudo-elements.
+///
+/// We use an Arc so that sharing these styles via the style sharing cache does
+/// not require duplicate allocations. We leverage the copy-on-write semantics of
+/// Arc::make_mut(), which is free (i.e. does not require atomic RMU operations)
+/// in servo_arc.
+#[derive(Clone, Debug, Default)]
+pub struct EagerPseudoStyles(Option<Arc<EagerPseudoArray>>);
+
+#[derive(Default)]
+struct EagerPseudoArray(EagerPseudoArrayInner);
+type EagerPseudoArrayInner = [Option<Arc<ComputedValues>>; EAGER_PSEUDO_COUNT];
+
+impl Deref for EagerPseudoArray {
+    type Target = EagerPseudoArrayInner;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for EagerPseudoArray {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+// Manually implement `Clone` here because the derived impl of `Clone` for
+// array types assumes the value inside is `Copy`.
+impl Clone for EagerPseudoArray {
+    fn clone(&self) -> Self {
+        let mut clone = Self::default();
+        for i in 0..EAGER_PSEUDO_COUNT {
+            clone[i] = self.0[i].clone();
+        }
+        clone
+    }
+}
+
+// Override Debug to print which pseudos we have, and substitute the rule node
+// for the much-more-verbose ComputedValues stringification.
+impl fmt::Debug for EagerPseudoArray {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "EagerPseudoArray {{ ")?;
+        for i in 0..EAGER_PSEUDO_COUNT {
+            if let Some(ref values) = self[i] {
+                write!(
+                    f,
+                    "{:?}: {:?}, ",
+                    PseudoElement::from_eager_index(i),
+                    &values.rules
+                )?;
+            }
+        }
+        write!(f, "}}")
+    }
+}
+
+// Can't use [None; EAGER_PSEUDO_COUNT] here because it complains
+// about Copy not being implemented for our Arc type.
+#[cfg(feature = "gecko")]
+const EMPTY_PSEUDO_ARRAY: &'static EagerPseudoArrayInner = &[None, None, None, None];
+#[cfg(feature = "servo")]
+const EMPTY_PSEUDO_ARRAY: &'static EagerPseudoArrayInner = &[None, None, None];
+
+impl EagerPseudoStyles {
+    /// Returns whether there are any pseudo styles.
+    pub fn is_empty(&self) -> bool {
+        self.0.is_none()
+    }
+
+    /// Grabs a reference to the list of styles, if they exist.
+    pub fn as_optional_array(&self) -> Option<&EagerPseudoArrayInner> {
+        match self.0 {
+            None => None,
+            Some(ref x) => Some(&x.0),
+        }
+    }
+
+    /// Grabs a reference to the list of styles or a list of None if
+    /// there are no styles to be had.
+    pub fn as_array(&self) -> &EagerPseudoArrayInner {
+        self.as_optional_array().unwrap_or(EMPTY_PSEUDO_ARRAY)
+    }
+
+    /// Returns a reference to the style for a given eager pseudo, if it exists.
+    pub fn get(&self, pseudo: &PseudoElement) -> Option<&Arc<ComputedValues>> {
+        debug_assert!(pseudo.is_eager());
+        self.0
+            .as_ref()
+            .and_then(|p| p[pseudo.eager_index()].as_ref())
+    }
+
+    /// Sets the style for the eager pseudo.
+    pub fn set(&mut self, pseudo: &PseudoElement, value: Arc<ComputedValues>) {
+        if self.0.is_none() {
+            self.0 = Some(Arc::new(Default::default()));
+        }
+        let arr = Arc::make_mut(self.0.as_mut().unwrap());
+        arr[pseudo.eager_index()] = Some(value);
+    }
+}
+
+/// The styles associated with a node, including the styles for any
+/// pseudo-elements.
+#[derive(Clone, Default)]
+pub struct ElementStyles {
+    /// The element's style.
+    pub primary: Option<Arc<ComputedValues>>,
+    /// A list of the styles for the element's eagerly-cascaded pseudo-elements.
+    pub pseudos: EagerPseudoStyles,
+}
+
+// There's one of these per rendered elements so it better be small.
+size_of_test!(ElementStyles, 16);
+
+/// Information on how this element uses viewport units.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub enum ViewportUnitUsage {
+    /// No viewport units are used.
+    None = 0,
+    /// There are viewport units used from regular style rules (which means we
+    /// should re-cascade).
+    FromDeclaration,
+    /// There are viewport units used from container queries (which means we
+    /// need to re-selector-match).
+    FromQuery,
+}
+
+impl ElementStyles {
+    /// Returns the primary style.
+    pub fn get_primary(&self) -> Option<&Arc<ComputedValues>> {
+        self.primary.as_ref()
+    }
+
+    /// Returns the primary style.  Panic if no style available.
+    pub fn primary(&self) -> &Arc<ComputedValues> {
+        self.primary.as_ref().unwrap()
+    }
+
+    /// Whether this element `display` value is `none`.
+    pub fn is_display_none(&self) -> bool {
+        self.primary().get_box().clone_display().is_none()
+    }
+
+    /// Whether this element uses viewport units.
+    pub fn viewport_unit_usage(&self) -> ViewportUnitUsage {
+        fn usage_from_flags(flags: ComputedValueFlags) -> ViewportUnitUsage {
+            if flags.intersects(ComputedValueFlags::USES_VIEWPORT_UNITS_ON_CONTAINER_QUERIES) {
+                return ViewportUnitUsage::FromQuery;
+            }
+            if flags.intersects(ComputedValueFlags::USES_VIEWPORT_UNITS) {
+                return ViewportUnitUsage::FromDeclaration;
+            }
+            ViewportUnitUsage::None
+        }
+
+        let mut usage = usage_from_flags(self.primary().flags);
+        for pseudo_style in self.pseudos.as_array() {
+            if let Some(ref pseudo_style) = pseudo_style {
+                usage = std::cmp::max(usage, usage_from_flags(pseudo_style.flags));
+            }
+        }
+
+        usage
+    }
+
+    #[cfg(feature = "gecko")]
+    fn size_of_excluding_cvs(&self, _ops: &mut MallocSizeOfOps) -> usize {
+        // As the method name suggests, we don't measures the ComputedValues
+        // here, because they are measured on the C++ side.
+
+        // XXX: measure the EagerPseudoArray itself, but not the ComputedValues
+        // within it.
+
+        0
+    }
+}
+
+// We manually implement Debug for ElementStyles so that we can avoid the
+// verbose stringification of every property in the ComputedValues. We
+// substitute the rule node instead.
+impl fmt::Debug for ElementStyles {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "ElementStyles {{ primary: {:?}, pseudos: {:?} }}",
+            self.primary.as_ref().map(|x| &x.rules),
+            self.pseudos
+        )
+    }
+}
+
+/// Style system data associated with an Element.
+///
+/// In Gecko, this hangs directly off the Element. Servo, this is embedded
+/// inside of layout data, which itself hangs directly off the Element. In
+/// both cases, it is wrapped inside an AtomicRefCell to ensure thread safety.
+#[derive(Debug, Default)]
+pub struct ElementData {
+    /// The styles for the element and its pseudo-elements.
+    pub styles: ElementStyles,
+
+    /// The restyle damage, indicating what kind of layout changes are required
+    /// afte restyling.
+    pub damage: RestyleDamage,
+
+    /// The restyle hint, which indicates whether selectors need to be rematched
+    /// for this element, its children, and its descendants.
+    pub hint: RestyleHint,
+
+    /// Flags.
+    pub flags: ElementDataFlags,
+}
+
+// There's one of these per rendered elements so it better be small.
+size_of_test!(ElementData, 24);
+
+/// The kind of restyle that a single element should do.
+#[derive(Debug)]
+pub enum RestyleKind {
+    /// We need to run selector matching plus re-cascade, that is, a full
+    /// restyle.
+    MatchAndCascade,
+    /// We need to recascade with some replacement rule, such as the style
+    /// attribute, or animation rules.
+    CascadeWithReplacements(RestyleHint),
+    /// We only need to recascade, for example, because only inherited
+    /// properties in the parent changed.
+    CascadeOnly,
+}
+
+impl ElementData {
+    /// Invalidates style for this element, its descendants, and later siblings,
+    /// based on the snapshot of the element that we took when attributes or
+    /// state changed.
+    pub fn invalidate_style_if_needed<'a, E: TElement>(
+        &mut self,
+        element: E,
+        shared_context: &SharedStyleContext,
+        stack_limit_checker: Option<&StackLimitChecker>,
+        selector_caches: &'a mut SelectorCaches,
+    ) -> InvalidationResult {
+        // In animation-only restyle we shouldn't touch snapshot at all.
+        if shared_context.traversal_flags.for_animation_only() {
+            return InvalidationResult::empty();
+        }
+
+        use crate::invalidation::element::invalidator::TreeStyleInvalidator;
+        use crate::invalidation::element::state_and_attributes::StateAndAttrInvalidationProcessor;
+
+        debug!(
+            "invalidate_style_if_needed: {:?}, flags: {:?}, has_snapshot: {}, \
+             handled_snapshot: {}, pseudo: {:?}",
+            element,
+            shared_context.traversal_flags,
+            element.has_snapshot(),
+            element.handled_snapshot(),
+            element.implemented_pseudo_element()
+        );
+
+        if !element.has_snapshot() || element.handled_snapshot() {
+            return InvalidationResult::empty();
+        }
+
+        let mut processor =
+            StateAndAttrInvalidationProcessor::new(shared_context, element, self, selector_caches);
+
+        let invalidator = TreeStyleInvalidator::new(element, stack_limit_checker, &mut processor);
+
+        let result = invalidator.invalidate();
+
+        unsafe { element.set_handled_snapshot() }
+        debug_assert!(element.handled_snapshot());
+
+        result
+    }
+
+    /// Returns true if this element has styles.
+    #[inline]
+    pub fn has_styles(&self) -> bool {
+        self.styles.primary.is_some()
+    }
+
+    /// Returns this element's styles as resolved styles to use for sharing.
+    pub fn share_styles(&self) -> ResolvedElementStyles {
+        ResolvedElementStyles {
+            primary: self.share_primary_style(),
+            pseudos: self.styles.pseudos.clone(),
+        }
+    }
+
+    /// Returns this element's primary style as a resolved style to use for sharing.
+    pub fn share_primary_style(&self) -> PrimaryStyle {
+        let reused_via_rule_node = self
+            .flags
+            .contains(ElementDataFlags::PRIMARY_STYLE_REUSED_VIA_RULE_NODE);
+
+        PrimaryStyle {
+            style: ResolvedStyle(self.styles.primary().clone()),
+            reused_via_rule_node,
+        }
+    }
+
+    /// Sets a new set of styles, returning the old ones.
+    pub fn set_styles(&mut self, new_styles: ResolvedElementStyles) -> ElementStyles {
+        if new_styles.primary.reused_via_rule_node {
+            self.flags
+                .insert(ElementDataFlags::PRIMARY_STYLE_REUSED_VIA_RULE_NODE);
+        } else {
+            self.flags
+                .remove(ElementDataFlags::PRIMARY_STYLE_REUSED_VIA_RULE_NODE);
+        }
+        mem::replace(&mut self.styles, new_styles.into())
+    }
+
+    /// Returns the kind of restyling that we're going to need to do on this
+    /// element, based of the stored restyle hint.
+    pub fn restyle_kind(&self, shared_context: &SharedStyleContext) -> Option<RestyleKind> {
+        if shared_context.traversal_flags.for_animation_only() {
+            return self.restyle_kind_for_animation(shared_context);
+        }
+
+        let style = match self.styles.primary {
+            Some(ref s) => s,
+            None => return Some(RestyleKind::MatchAndCascade),
+        };
+
+        let hint = self.hint;
+        if hint.is_empty() {
+            return None;
+        }
+
+        let needs_to_match_self = hint.intersects(RestyleHint::RESTYLE_SELF) ||
+            (hint.intersects(RestyleHint::RESTYLE_SELF_IF_PSEUDO) && style.is_pseudo_style());
+        if needs_to_match_self {
+            return Some(RestyleKind::MatchAndCascade);
+        }
+
+        if hint.has_replacements() {
+            debug_assert!(
+                !hint.has_animation_hint(),
+                "Animation only restyle hint should have already processed"
+            );
+            return Some(RestyleKind::CascadeWithReplacements(
+                hint & RestyleHint::replacements(),
+            ));
+        }
+
+        let needs_to_recascade_self = hint.intersects(RestyleHint::RECASCADE_SELF) ||
+            (hint.intersects(RestyleHint::RECASCADE_SELF_IF_INHERIT_RESET_STYLE) &&
+                style
+                    .flags
+                    .contains(ComputedValueFlags::INHERITS_RESET_STYLE));
+        if needs_to_recascade_self {
+            return Some(RestyleKind::CascadeOnly);
+        }
+
+        None
+    }
+
+    /// Returns the kind of restyling for animation-only restyle.
+    fn restyle_kind_for_animation(
+        &self,
+        shared_context: &SharedStyleContext,
+    ) -> Option<RestyleKind> {
+        debug_assert!(shared_context.traversal_flags.for_animation_only());
+        debug_assert!(
+            self.has_styles(),
+            "animation traversal doesn't care about unstyled elements"
+        );
+
+        // FIXME: We should ideally restyle here, but it is a hack to work around our weird
+        // animation-only traversal stuff: If we're display: none and the rules we could
+        // match could change, we consider our style up-to-date. This is because re-cascading with
+        // and old style doesn't guarantee returning the correct animation style (that's
+        // bug 1393323). So if our display changed, and it changed from display: none, we would
+        // incorrectly forget about it and wouldn't be able to correctly style our descendants
+        // later.
+        // XXX Figure out if this still makes sense.
+        let hint = self.hint;
+        if self.styles.is_display_none() && hint.intersects(RestyleHint::RESTYLE_SELF) {
+            return None;
+        }
+
+        let style = self.styles.primary();
+        // Return either CascadeWithReplacements or CascadeOnly in case of
+        // animation-only restyle. I.e. animation-only restyle never does
+        // selector matching.
+        if hint.has_animation_hint() {
+            return Some(RestyleKind::CascadeWithReplacements(
+                hint & RestyleHint::for_animations(),
+            ));
+        }
+
+        let needs_to_recascade_self = hint.intersects(RestyleHint::RECASCADE_SELF) ||
+            (hint.intersects(RestyleHint::RECASCADE_SELF_IF_INHERIT_RESET_STYLE) &&
+                style
+                    .flags
+                    .contains(ComputedValueFlags::INHERITS_RESET_STYLE));
+        if needs_to_recascade_self {
+            return Some(RestyleKind::CascadeOnly);
+        }
+        return None;
+    }
+
+    /// Drops any restyle state from the element.
+    ///
+    /// FIXME(bholley): The only caller of this should probably just assert that
+    /// the hint is empty and call clear_flags_and_damage().
+    #[inline]
+    pub fn clear_restyle_state(&mut self) {
+        self.hint = RestyleHint::empty();
+        self.clear_restyle_flags_and_damage();
+    }
+
+    /// Drops restyle flags and damage from the element.
+    #[inline]
+    pub fn clear_restyle_flags_and_damage(&mut self) {
+        self.damage = RestyleDamage::empty();
+        self.flags.remove(ElementDataFlags::WAS_RESTYLED);
+    }
+
+    /// Mark this element as restyled, which is useful to know whether we need
+    /// to do a post-traversal.
+    pub fn set_restyled(&mut self) {
+        self.flags.insert(ElementDataFlags::WAS_RESTYLED);
+        self.flags
+            .remove(ElementDataFlags::TRAVERSED_WITHOUT_STYLING);
+    }
+
+    /// Returns true if this element was restyled.
+    #[inline]
+    pub fn is_restyle(&self) -> bool {
+        self.flags.contains(ElementDataFlags::WAS_RESTYLED)
+    }
+
+    /// Mark that we traversed this element without computing any style for it.
+    pub fn set_traversed_without_styling(&mut self) {
+        self.flags
+            .insert(ElementDataFlags::TRAVERSED_WITHOUT_STYLING);
+    }
+
+    /// Returns whether this element has been part of a restyle.
+    #[inline]
+    pub fn contains_restyle_data(&self) -> bool {
+        self.is_restyle() || !self.hint.is_empty() || !self.damage.is_empty()
+    }
+
+    /// Returns whether it is safe to perform cousin sharing based on the ComputedValues
+    /// identity of the primary style in this ElementData. There are a few subtle things
+    /// to check.
+    ///
+    /// First, if a parent element was already styled and we traversed past it without
+    /// restyling it, that may be because our clever invalidation logic was able to prove
+    /// that the styles of that element would remain unchanged despite changes to the id
+    /// or class attributes. However, style sharing relies on the strong guarantee that all
+    /// the classes and ids up the respective parent chains are identical. As such, if we
+    /// skipped styling for one (or both) of the parents on this traversal, we can't share
+    /// styles across cousins. Note that this is a somewhat conservative check. We could
+    /// tighten it by having the invalidation logic explicitly flag elements for which it
+    /// ellided styling.
+    ///
+    /// Second, we want to only consider elements whose ComputedValues match due to a hit
+    /// in the style sharing cache, rather than due to the rule-node-based reuse that
+    /// happens later in the styling pipeline. The former gives us the stronger guarantees
+    /// we need for style sharing, the latter does not.
+    pub fn safe_for_cousin_sharing(&self) -> bool {
+        if self.flags.intersects(
+            ElementDataFlags::TRAVERSED_WITHOUT_STYLING |
+                ElementDataFlags::PRIMARY_STYLE_REUSED_VIA_RULE_NODE,
+        ) {
+            return false;
+        }
+        if !self
+            .styles
+            .primary()
+            .get_box()
+            .clone_container_type()
+            .is_normal()
+        {
+            return false;
+        }
+        true
+    }
+
+    /// Measures memory usage.
+    #[cfg(feature = "gecko")]
+    pub fn size_of_excluding_cvs(&self, ops: &mut MallocSizeOfOps) -> usize {
+        let n = self.styles.size_of_excluding_cvs(ops);
+
+        // We may measure more fields in the future if DMD says it's worth it.
+
+        n
+    }
+}