servo: Merge #19368 - Bug 951793 - Add support for the 'overscroll-behavior' CSS property (Servo changes) (from theres-waldo:bug951793); r=emilio

Servo changes for [bug 951793](https://bugzilla.mozilla.org/show_bug.cgi?id=951793).

Source-Repo: https://github.com/servo/servo
Source-Revision: 6158a4bf91d8d38900c5fec8bb20ff219e444f61

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : b3142a8aae8deb3d9c00a3907f30bde63b570fdd

servo/components/style/properties/gecko.mako.rs

@@ -3099,6 +3099,8 @@ fn static_assert() {
                           scroll-snap-points-x scroll-snap-points-y
                           scroll-snap-type-x scroll-snap-type-y scroll-snap-coordinate
                           perspective-origin -moz-binding will-change
+                          overscroll-behavior-x overscroll-behavior-y
+                          perspective-origin -moz-binding will-change
                           shape-outside contain touch-action""" %>
 <%self:impl_trait style_struct_name="Box" skip_longhands="${skip_box_longhands}">
 
@@ -3486,6 +3488,11 @@ fn static_assert() {
     ${impl_keyword('scroll_snap_type_y', 'mScrollSnapTypeY', scroll_snap_type_keyword)}
     ${impl_keyword('scroll_snap_type_x', 'mScrollSnapTypeX', scroll_snap_type_keyword)}
 
+    <% overscroll_behavior_keyword = Keyword("overscroll-behavior", "Auto Contain None",
+                                             gecko_enum_prefix="StyleOverscrollBehavior") %>
+    ${impl_keyword('overscroll_behavior_x', 'mOverscrollBehaviorX', overscroll_behavior_keyword)}
+    ${impl_keyword('overscroll_behavior_y', 'mOverscrollBehaviorY', overscroll_behavior_keyword)}
+
     pub fn set_perspective_origin(&mut self, v: longhands::perspective_origin::computed_value::T) {
         self.gecko.mPerspectiveOrigin[0].set(v.horizontal);
         self.gecko.mPerspectiveOrigin[1].set(v.vertical);

servo/components/style/properties/longhand/box.mako.rs

@@ -601,6 +601,19 @@ ${helpers.single_keyword("scroll-behavior",
     )}
 % endfor
 
+% for axis in ["x", "y"]:
+    ${helpers.predefined_type(
+        "overscroll-behavior-" + axis,
+        "OverscrollBehavior",
+        "computed::OverscrollBehavior::Auto",
+        products="gecko",
+        needs_context=False,
+        gecko_pref="layout.css.overscroll-behavior.enabled",
+        spec="https://wicg.github.io/overscroll-behavior/#overscroll-behavior-properties",
+        animation_value_type="discrete"
+    )}
+% endfor
+
 // Compositing and Blending Level 1
 // http://www.w3.org/TR/compositing-1/
 ${helpers.single_keyword("isolation",

servo/components/style/properties/shorthand/box.mako.rs

@@ -346,7 +346,7 @@ macro_rules! try_parse_one {
     }
 
     impl<'a> ToCss for LonghandsToSerialize<'a>  {
-        // Serializes into the single keyword value if both scroll-snap-type and scroll-snap-type-y are same.
+        // Serializes into the single keyword value if both scroll-snap-type-x and scroll-snap-type-y are same.
         // Otherwise into an empty string. This is done to match Gecko's behaviour.
         fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
             if self.scroll_snap_type_x == self.scroll_snap_type_y {
@@ -358,6 +358,36 @@ macro_rules! try_parse_one {
     }
 </%helpers:shorthand>
 
+<%helpers:shorthand name="overscroll-behavior" products="gecko"
+                    gecko_pref="layout.css.overscroll-behavior.enabled"
+                    sub_properties="overscroll-behavior-x overscroll-behavior-y"
+                    spec="https://wicg.github.io/overscroll-behavior/#overscroll-behavior-properties">
+    pub fn parse_value<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>
+    ) -> Result<Longhands, ParseError<'i>> {
+        use values::specified::OverscrollBehavior;
+        let behavior_x = OverscrollBehavior::parse(input)?;
+        let behavior_y = input.try(OverscrollBehavior::parse).unwrap_or(behavior_x);
+        Ok(expanded! {
+            overscroll_behavior_x: behavior_x,
+            overscroll_behavior_y: behavior_y,
+        })
+    }
+
+    impl<'a> ToCss for LonghandsToSerialize<'a> {
+        // Serializes into the single keyword value if both overscroll-behavior-x and overscroll-behavior-y are same.
+        // Otherwise into two values separated by a space.
+        fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+            self.overscroll_behavior_x.to_css(dest)?;
+            if self.overscroll_behavior_y != self.overscroll_behavior_x {
+                dest.write_str(" ")?;
+                self.overscroll_behavior_y.to_css(dest)?;
+            }
+            Ok(())
+        }
+    }
+</%helpers:shorthand>
 
 <%helpers:shorthand name="-moz-transform" products="gecko"
                     sub_properties="transform"

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

@@ -9,7 +9,7 @@ use values::computed::length::LengthOrPercentage;
 use values::generics::box_::AnimationIterationCount as GenericAnimationIterationCount;
 use values::generics::box_::VerticalAlign as GenericVerticalAlign;
 
-pub use values::specified::box_::{AnimationName, ScrollSnapType};
+pub use values::specified::box_::{AnimationName, OverscrollBehavior, ScrollSnapType};
 
 /// A computed value for the `vertical-align` property.
 pub type VerticalAlign = GenericVerticalAlign<LengthOrPercentage>;

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

@@ -40,7 +40,7 @@ pub use self::font::{FontSize, FontSizeAdjust, FontSynthesis, FontWeight, FontVa
 pub use self::font::{FontLanguageOverride, FontVariantSettings, FontVariantEastAsian};
 pub use self::font::{FontVariantLigatures, FontVariantNumeric, FontFeatureSettings};
 pub use self::font::{MozScriptLevel, MozScriptMinSize, MozScriptSizeMultiplier, XTextZoom, XLang};
-pub use self::box_::{AnimationIterationCount, AnimationName, ScrollSnapType, VerticalAlign};
+pub use self::box_::{AnimationIterationCount, AnimationName, OverscrollBehavior, ScrollSnapType, VerticalAlign};
 pub use self::color::{Color, ColorPropertyValue, RGBAColor};
 pub use self::effects::{BoxShadow, Filter, SimpleShadow};
 pub use self::flex::FlexBasis;

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

@@ -117,3 +117,10 @@ define_css_keyword_enum! { ScrollSnapType:
     "proximity" => Proximity,
 }
 add_impls_for_keyword_enum!(ScrollSnapType);
+
+define_css_keyword_enum! { OverscrollBehavior:
+    "auto" => Auto,
+    "contain" => Contain,
+    "none" => None,
+}
+add_impls_for_keyword_enum!(OverscrollBehavior);

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

@@ -34,7 +34,7 @@ pub use self::font::{FontSize, FontSizeAdjust, FontSynthesis, FontWeight, FontVa
 pub use self::font::{FontLanguageOverride, FontVariantSettings, FontVariantEastAsian};
 pub use self::font::{FontVariantLigatures, FontVariantNumeric, FontFeatureSettings};
 pub use self::font::{MozScriptLevel, MozScriptMinSize, MozScriptSizeMultiplier, XTextZoom, XLang};
-pub use self::box_::{AnimationIterationCount, AnimationName, ScrollSnapType, VerticalAlign};
+pub use self::box_::{AnimationIterationCount, AnimationName, OverscrollBehavior, ScrollSnapType, VerticalAlign};
 pub use self::color::{Color, ColorPropertyValue, RGBAColor};
 pub use self::effects::{BoxShadow, Filter, SimpleShadow};
 pub use self::flex::FlexBasis;