style: Add support for parsing the content-visibility property from the CSS Contain specification

Add initial parsing support for the CSS `content-visibility` attribute.
Currently these parsed values have no effect.

Differential Revision: https://phabricator.services.mozilla.com/D140834

components/style/properties/counted_unknown_properties.py

@@ -120,5 +120,4 @@ COUNTED_UNKNOWN_PROPERTIES = [
     "-webkit-columns",
     "-webkit-column-rule-color",
     "-webkit-shape-margin",
-    "content-visibility",
 ]

components/style/properties/data.py

@@ -462,6 +462,7 @@ class Longhand(Property):
                 "Clear",
                 "ColumnCount",
                 "Contain",
+                "ContentVisibility",
                 "Display",
                 "FillRule",
                 "Float",

components/style/properties/longhands/box.mako.rs

@@ -613,6 +613,16 @@ ${helpers.predefined_type(
     spec="https://drafts.csswg.org/css-contain/#contain-property",
 )}
 
+${helpers.predefined_type(
+    "content-visibility",
+    "ContentVisibility",
+    "computed::ContentVisibility::Visible",
+    engines="gecko",
+    spec="https://drafts.csswg.org/css-contain/#content-visibility",
+    gecko_pref="layout.css.content-visibility.enabled",
+    animation_value_type="none",
+)}
+
 ${helpers.predefined_type(
     "appearance",
     "Appearance",

components/style/values/computed/box.rs

@@ -13,9 +13,9 @@ use crate::values::specified::box_ as specified;
 
 pub use crate::values::specified::box_::{
     AnimationName, AnimationTimeline, Appearance, BreakBetween, BreakWithin,
-    Clear as SpecifiedClear, Contain, Display, Float as SpecifiedFloat, Overflow, OverflowAnchor,
-    OverflowClipBox, OverscrollBehavior, ScrollSnapAlign, ScrollSnapAxis, ScrollSnapStrictness,
-    ScrollSnapType, ScrollbarGutter, TouchAction, TransitionProperty, WillChange,
+    Clear as SpecifiedClear, Contain, ContentVisibility, Display, Float as SpecifiedFloat, Overflow,
+    OverflowAnchor, OverflowClipBox, OverscrollBehavior, ScrollSnapAlign, ScrollSnapAxis,
+    ScrollSnapStrictness, ScrollSnapType, ScrollbarGutter, TouchAction, TransitionProperty, WillChange,
 };
 
 /// A computed value for the `vertical-align` property.

components/style/values/computed/mod.rs

@@ -45,7 +45,7 @@ pub use self::border::{BorderCornerRadius, BorderRadius, BorderSpacing};
 pub use self::border::{BorderImageRepeat, BorderImageSideWidth};
 pub use self::border::{BorderImageSlice, BorderImageWidth};
 pub use self::box_::{AnimationIterationCount, AnimationName, AnimationTimeline, Contain};
-pub use self::box_::{Appearance, BreakBetween, BreakWithin, Clear, Float};
+pub use self::box_::{Appearance, BreakBetween, BreakWithin, Clear, ContentVisibility, Float};
 pub use self::box_::{Display, Overflow, OverflowAnchor, TransitionProperty};
 pub use self::box_::{OverflowClipBox, OverscrollBehavior, Perspective, Resize, ScrollbarGutter};
 pub use self::box_::{ScrollSnapAlign, ScrollSnapAxis, ScrollSnapStrictness, ScrollSnapType};

components/style/values/specified/box.rs

@@ -1450,6 +1450,34 @@ impl Parse for Contain {
     }
 }
 
+#[allow(missing_docs)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Eq,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(u8)]
+pub enum ContentVisibility {
+    /// `auto` variant, the element turns on layout containment, style containment, and paint
+    /// containment. In addition, if the element is not relevant to the user (such as by being
+    /// offscreen) it also skips its content
+    Auto,
+    /// `hidden` variant, the element skips its content
+    Hidden,
+    /// 'visible' variant, no effect
+    Visible,
+}
+
 /// A specified value for the `perspective` property.
 pub type Perspective = GenericPerspective<NonNegativeLength>;
 

components/style/values/specified/mod.rs

@@ -38,7 +38,7 @@ pub use self::border::{BorderImageRepeat, BorderImageSideWidth};
 pub use self::border::{BorderRadius, BorderSideWidth, BorderSpacing, BorderStyle};
 pub use self::box_::{AnimationIterationCount, AnimationName, AnimationTimeline, Contain, Display};
 pub use self::box_::{Appearance, BreakBetween, BreakWithin};
-pub use self::box_::{Clear, Float, Overflow, OverflowAnchor};
+pub use self::box_::{Clear, ContentVisibility, Float, Overflow, OverflowAnchor};
 pub use self::box_::{OverflowClipBox, OverscrollBehavior, Perspective, Resize, ScrollbarGutter};
 pub use self::box_::{ScrollSnapAlign, ScrollSnapAxis, ScrollSnapStrictness, ScrollSnapType};
 pub use self::box_::{TouchAction, TransitionProperty, VerticalAlign, WillChange};