style: Implement scroll-snap-align parser and serializer.

https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-align

Differential Revision: https://phabricator.services.mozilla.com/D20205

components/style/cbindgen.toml

@@ -70,6 +70,7 @@ include = [
   "UserSelect",
   "Float",
   "OverscrollBehavior",
+  "ScrollSnapAlign",
   "ScrollSnapType",
   "OverflowAnchor",
   "OverflowClipBox",

components/style/properties/data.py

@@ -339,6 +339,7 @@ class Longhand(object):
                 "Resize",
                 "SVGOpacity",
                 "SVGPaintOrder",
+                "ScrollSnapAlign",
                 "ScrollSnapType",
                 "TextAlign",
                 "TextDecorationLine",

components/style/properties/gecko.mako.rs

@@ -1354,6 +1354,7 @@ impl Clone for ${style_struct.gecko_struct_name} {
         "Appearance": impl_simple,
         "OverscrollBehavior": impl_simple,
         "OverflowClipBox": impl_simple,
+        "ScrollSnapAlign": impl_simple,
         "ScrollSnapType": impl_simple,
         "Float": impl_simple,
         "Overflow": impl_simple,

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

@@ -417,6 +417,16 @@ ${helpers.single_keyword(
     animation_value_type="discrete",
 )}
 
+${helpers.predefined_type(
+    "scroll-snap-align",
+    "ScrollSnapAlign",
+    "computed::ScrollSnapAlign::none()",
+    products="gecko",
+    gecko_pref="layout.css.scroll-snap-v1.enabled",
+    spec="https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-align",
+    animation_value_type="discrete",
+)}
+
 % for axis in ["x", "y"]:
     ${helpers.predefined_type(
         "scroll-snap-type-" + axis,

components/style/values/computed/box.rs

@@ -15,7 +15,7 @@ pub use crate::values::specified::box_::{AnimationName, Appearance, BreakBetween
 pub use crate::values::specified::box_::{Clear as SpecifiedClear, Float as SpecifiedFloat};
 pub use crate::values::specified::box_::{Contain, Display, Overflow};
 pub use crate::values::specified::box_::{OverflowAnchor, OverflowClipBox};
-pub use crate::values::specified::box_::{OverscrollBehavior, ScrollSnapType};
+pub use crate::values::specified::box_::{OverscrollBehavior, ScrollSnapAlign, ScrollSnapType};
 pub use crate::values::specified::box_::{TouchAction, TransitionProperty, WillChange};
 
 /// A computed value for the `vertical-align` property.

components/style/values/computed/mod.rs

@@ -44,7 +44,7 @@ pub use self::box_::{AnimationIterationCount, AnimationName, Contain};
 pub use self::box_::{Appearance, BreakBetween, BreakWithin, Clear, Float};
 pub use self::box_::{Display, Overflow, OverflowAnchor, TransitionProperty};
 pub use self::box_::{OverflowClipBox, OverscrollBehavior, Perspective, Resize};
-pub use self::box_::{ScrollSnapType, TouchAction, VerticalAlign, WillChange};
+pub use self::box_::{ScrollSnapAlign, ScrollSnapType, TouchAction, VerticalAlign, WillChange};
 pub use self::color::{Color, ColorPropertyValue, RGBAColor};
 pub use self::column::ColumnCount;
 pub use self::counters::{Content, ContentItem, CounterIncrement, CounterReset};

components/style/values/specified/box.rs

@@ -392,6 +392,86 @@ pub enum ScrollSnapType {
     Proximity,
 }
 
+/// Specified value of scroll-snap-align keyword value.
+#[allow(missing_docs)]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Eq,
+    FromPrimitive,
+    Hash,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+)]
+#[repr(u8)]
+pub enum ScrollSnapAlignKeyword {
+    None,
+    Start,
+    End,
+    Center,
+}
+
+/// https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-align
+#[allow(missing_docs)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Eq,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+)]
+#[repr(C)]
+pub struct ScrollSnapAlign {
+    block: ScrollSnapAlignKeyword,
+    inline: ScrollSnapAlignKeyword,
+}
+
+impl ScrollSnapAlign {
+    /// Returns `none`.
+    #[inline]
+    pub fn none() -> Self {
+        ScrollSnapAlign {
+            block: ScrollSnapAlignKeyword::None,
+            inline: ScrollSnapAlignKeyword::None,
+        }
+    }
+}
+
+impl Parse for ScrollSnapAlign {
+    /// [ none | start | end | center ]{1,2}
+    fn parse<'i, 't>(
+        _context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<ScrollSnapAlign, ParseError<'i>> {
+        let block = ScrollSnapAlignKeyword::parse(input)?;
+        let inline = input.try(ScrollSnapAlignKeyword::parse).unwrap_or(block);
+        Ok(ScrollSnapAlign { block, inline })
+    }
+}
+
+impl ToCss for ScrollSnapAlign {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        self.block.to_css(dest)?;
+        if self.block != self.inline {
+            dest.write_str(" ")?;
+            self.inline.to_css(dest)?;
+        }
+        Ok(())
+    }
+}
+
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 #[derive(

components/style/values/specified/mod.rs

@@ -39,7 +39,8 @@ pub use self::box_::{AnimationIterationCount, AnimationName, Contain, Display};
 pub use self::box_::{Appearance, BreakBetween, BreakWithin};
 pub use self::box_::{Clear, Float, Overflow, OverflowAnchor};
 pub use self::box_::{OverflowClipBox, OverscrollBehavior, Perspective, Resize};
-pub use self::box_::{ScrollSnapType, TouchAction, TransitionProperty, VerticalAlign, WillChange};
+pub use self::box_::{ScrollSnapAlign, ScrollSnapType};
+pub use self::box_::{TouchAction, TransitionProperty, VerticalAlign, WillChange};
 pub use self::color::{Color, ColorPropertyValue, RGBAColor};
 pub use self::column::ColumnCount;
 pub use self::counters::{Content, ContentItem, CounterIncrement, CounterReset};