Bug 1956645 - Parse and serialize view-transition-class. r=view-transitions-reviewers,firefox-style-system-reviewers,emilio

Parse and serialize `view-transition-class: none | <custom-ident>+`.
This property will be used after we extend `<pt-name-selector>` to
`<pt-name-and-class-selector>` for named view transition pseudo-elements.
Will do this in Bug 1956646. Also, we will handle the class matching in
Bug 1964949.

Differential Revision: https://phabricator.services.mozilla.com/D249681

servo/components/style/properties/longhands/ui.mako.rs

@@ -439,3 +439,16 @@ ${helpers.predefined_type(
     affects="",
     enabled_in="ua",
 )}
+
+${helpers.predefined_type(
+    "view-transition-class",
+    "ViewTransitionClass",
+    "computed::ViewTransitionClass::none()",
+    engines="gecko servo",
+    servo_pref="layout.unimplemented",
+    animation_type="discrete",
+    gecko_pref="dom.viewTransitions.enabled",
+    spec="https://drafts.csswg.org/css-view-transitions-2/#view-transition-class-prop",
+    affects="",
+    enabled_in="ua",
+)}

servo/components/style/values/computed/animation.rs

@@ -13,7 +13,8 @@ use style_traits::{CssWriter, ToCss};
 
 pub use crate::values::specified::animation::{
     AnimationComposition, AnimationDirection, AnimationFillMode, AnimationName, AnimationPlayState,
-    ScrollAxis, TimelineName, TransitionBehavior, TransitionProperty, ViewTransitionName,
+    ScrollAxis, TimelineName, TransitionBehavior, TransitionProperty, ViewTransitionClass,
+    ViewTransitionName,
 };
 
 /// A computed value for the `animation-duration` property.

servo/components/style/values/computed/mod.rs

@@ -43,7 +43,8 @@ pub use self::angle::Angle;
 pub use self::animation::{
     AnimationComposition, AnimationDirection, AnimationDuration, AnimationFillMode,
     AnimationIterationCount, AnimationName, AnimationPlayState, AnimationTimeline, ScrollAxis,
-    TimelineName, TransitionBehavior, TransitionProperty, ViewTimelineInset, ViewTransitionName,
+    TimelineName, TransitionBehavior, TransitionProperty, ViewTimelineInset, ViewTransitionClass,
+    ViewTransitionName,
 };
 pub use self::background::{BackgroundRepeat, BackgroundSize};
 pub use self::basic_shape::FillRule;

servo/components/style/values/specified/animation.rs

@@ -731,3 +731,58 @@ impl ToCss for ViewTransitionName {
         serialize_atom_identifier(&self.0, dest)
     }
 }
+
+/// The view-transition-class: `none | <custom-ident>+`.
+///
+/// https://drafts.csswg.org/css-view-transitions-2/#view-transition-class-prop
+///
+/// Empty slice represents `none`.
+#[derive(
+    Clone,
+    Debug,
+    Eq,
+    Hash,
+    PartialEq,
+    MallocSizeOf,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C)]
+#[value_info(other_values = "none")]
+pub struct ViewTransitionClass(
+    #[css(iterable, if_empty = "none")]
+    #[ignore_malloc_size_of = "Arc"]
+    crate::ArcSlice<CustomIdent>,
+);
+
+impl ViewTransitionClass {
+    /// Returns the default value, `none`. We use the default slice (i.e. empty) to represent it.
+    pub fn none() -> Self {
+        Self(Default::default())
+    }
+
+    /// Returns whether this is the `none` value.
+    pub fn is_none(&self) -> bool {
+        self.0.is_empty()
+    }
+}
+
+impl Parse for ViewTransitionClass {
+    fn parse<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        use style_traits::{Separator, Space};
+
+        if input.try_parse(|i| i.expect_ident_matching("none")).is_ok() {
+            return Ok(Self::none());
+        }
+
+        Ok(Self(crate::ArcSlice::from_iter(
+            Space::parse(input, |i| CustomIdent::parse(i, &["none"]))?.into_iter(),
+        )))
+    }
+}

servo/components/style/values/specified/mod.rs

@@ -31,7 +31,8 @@ pub use self::angle::{AllowUnitlessZeroAngle, Angle};
 pub use self::animation::{
     AnimationComposition, AnimationDirection, AnimationDuration, AnimationFillMode,
     AnimationIterationCount, AnimationName, AnimationPlayState, AnimationTimeline, ScrollAxis,
-    TimelineName, TransitionBehavior, TransitionProperty, ViewTimelineInset, ViewTransitionName,
+    TimelineName, TransitionBehavior, TransitionProperty, ViewTimelineInset, ViewTransitionClass,
+    ViewTransitionName,
 };
 pub use self::background::{BackgroundRepeat, BackgroundSize};
 pub use self::basic_shape::FillRule;

servo/ports/geckolib/cbindgen.toml

@@ -325,6 +325,7 @@ include = [
   "XTextScale",
   "Zoom",
   "TransitionProperty",
+  "ViewTransitionClass",
   "ViewTransitionName",
   "Inset",
   "AnchorFunction",