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style: Add ::marker when checking may_have_animations() during traver…
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When unhidding a ::marker element, we construct its generated item, and
then call StyleNewSubtree() on this generated item. During traversal, we
may update any animation related values in Gecko_UpdateAnimations(), which
may update the base styles for animation properties.

The test case is an animation segment from "null" to "inital" value. We
replace the "null" value with the base style value for the specific animation
property, so we can do interpolation properly.
(e.g. opacity: "null => initial" becomes "1.0 => initial")
If we don't update the animation related values in
Gecko_UpdateAnimations after generating ::marker, we may do
interpolation from "null" to "initial", which causes a panic.

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BorisChiou authored and emilio committed Jun 3, 2020
1 parent c67c9fd commit 6a7c0b7
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Showing 2 changed files with 7 additions and 1 deletion.
6 changes: 6 additions & 0 deletions components/style/gecko/
Expand Up @@ -92,6 +92,12 @@ impl PseudoElement {

/// Whether the current pseudo element is animatable.
pub fn is_animatable(&self) -> bool {
matches!(*self, Self::Before | Self::After | Self::Marker)

/// Whether the current pseudo element is ::before or ::after.
pub fn is_before_or_after(&self) -> bool {
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2 changes: 1 addition & 1 deletion components/style/gecko/
Expand Up @@ -1446,7 +1446,7 @@ impl<'le> TElement for GeckoElement<'le> {
fn may_have_animations(&self) -> bool {
if let Some(pseudo) = self.implemented_pseudo_element() {
if !pseudo.is_before_or_after() {
if !pseudo.is_animatable() {
return false;
// FIXME(emilio): When would the parent of a ::before / ::after
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