style: Initial support for the color-scheme CSS property

Add initial support for the color-scheme CSS property, allowing pages to
choose between light and dark system colors per-element, and such.

Things that are left to do so that this can be enabled by default:

 * Dark system colors on Windows / Android / Standins.
 * Dark Canvas/CanvasText/Link visited colors (which right now are set
   via PreferenceSheet).
 * Dark form controls in nsNativeBasicTheme.
 * Processing the color-scheme meta tag to fill-in
   Document::mColorSchemeBits.

But this seems like enough progress to be landable on its own.

Differential Revision: https://phabricator.services.mozilla.com/D120843

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

@@ -95,6 +95,17 @@ ${helpers.predefined_type(
     has_effect_on_gecko_scrollbars=False,
 )}
 
+${helpers.predefined_type(
+    "color-scheme",
+    "ColorScheme",
+    "specified::color::ColorScheme::normal()",
+    engines="gecko",
+    spec="https://drafts.csswg.org/css-color-adjust/#color-scheme-prop",
+    gecko_pref="layout.css.color-scheme.enabled",
+    animation_value_type="discrete",
+    has_effect_on_gecko_scrollbars=False,
+)}
+
 ${helpers.predefined_type(
     "scrollbar-color",
     "ui::ScrollbarColor",

components/style/properties/properties.mako.rs

@@ -1376,6 +1376,9 @@ impl LonghandId {
             LonghandId::FontStyle |
             LonghandId::FontFamily |
 
+            // color-scheme affects how system colors resolve.
+            LonghandId::ColorScheme |
+
             // Needed to properly compute the writing mode, to resolve logical
             // properties, and similar stuff.
             LonghandId::WritingMode |

components/style/values/computed/color.rs

@@ -11,6 +11,8 @@ use cssparser::{Color as CSSParserColor, RGBA};
 use std::fmt;
 use style_traits::{CssWriter, ToCss};
 
+pub use crate::values::specified::color::ColorScheme;
+
 /// The computed value of the `color` property.
 pub type ColorPropertyValue = RGBA;
 

components/style/values/computed/mod.rs

@@ -50,7 +50,7 @@ pub use self::box_::{Display, Overflow, OverflowAnchor, TransitionProperty};
 pub use self::box_::{OverflowClipBox, OverscrollBehavior, Perspective, Resize};
 pub use self::box_::{ScrollSnapAlign, ScrollSnapAxis, ScrollSnapStrictness, ScrollSnapType};
 pub use self::box_::{TouchAction, VerticalAlign, WillChange};
-pub use self::color::{Color, ColorOrAuto, ColorPropertyValue};
+pub use self::color::{Color, ColorOrAuto, ColorPropertyValue, ColorScheme};
 pub use self::column::ColumnCount;
 pub use self::counters::{Content, ContentItem, CounterIncrement, CounterSetOrReset};
 pub use self::easing::TimingFunction;

components/style/values/specified/color.rs

@@ -12,6 +12,7 @@ use crate::values::computed::{Color as ComputedColor, Context, ToComputedValue};
 use crate::values::generics::color::{GenericColorOrAuto, GenericCaretColor};
 use crate::values::specified::calc::CalcNode;
 use crate::values::specified::Percentage;
+use crate::values::CustomIdent;
 use cssparser::{AngleOrNumber, Color as CSSParserColor, Parser, Token, RGBA};
 use cssparser::{BasicParseErrorKind, NumberOrPercentage, ParseErrorKind};
 use itoa;
@@ -409,7 +410,10 @@ impl SystemColor {
         use crate::gecko_bindings::bindings;
 
         let colors = &cx.device().pref_sheet_prefs().mColors;
+        let style_color_scheme = cx.style().get_inherited_ui().clone_color_scheme();
 
+        // TODO: At least Canvas / CanvasText should be color-scheme aware
+        // (probably the link colors too).
         convert_nscolor_to_computedcolor(match *self {
             SystemColor::Canvastext => colors.mDefault,
             SystemColor::Canvas => colors.mDefaultBackground,
@@ -419,7 +423,7 @@ impl SystemColor {
 
             _ => {
                 let color = unsafe {
-                    bindings::Gecko_GetLookAndFeelSystemColor(*self as i32, cx.device().document(), scheme)
+                    bindings::Gecko_GetLookAndFeelSystemColor(*self as i32, cx.device().document(), scheme, &style_color_scheme)
                 };
                 if color == bindings::NS_SAME_AS_FOREGROUND_COLOR {
                     return ComputedColor::currentcolor();
@@ -876,3 +880,123 @@ impl Parse for CaretColor {
         ColorOrAuto::parse(context, input).map(GenericCaretColor)
     }
 }
+
+bitflags! {
+    /// Various flags to represent the color-scheme property in an efficient
+    /// way.
+    #[derive(Default, MallocSizeOf, SpecifiedValueInfo, ToComputedValue, ToResolvedValue, ToShmem)]
+    #[repr(C)]
+    #[value_info(other_values = "light,dark,only")]
+    pub struct ColorSchemeFlags: u8 {
+        /// Whether the author specified `light`.
+        const LIGHT = 1 << 0;
+        /// Whether the author specified `dark`.
+        const DARK = 1 << 1;
+        /// Whether the author specified `only`.
+        const ONLY = 1 << 2;
+    }
+}
+
+/// <https://drafts.csswg.org/css-color-adjust/#color-scheme-prop>
+#[derive(
+    Clone,
+    Debug,
+    Default,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C)]
+#[value_info(other_values = "normal")]
+pub struct ColorScheme {
+    #[ignore_malloc_size_of = "Arc"]
+    idents: crate::ArcSlice<CustomIdent>,
+    bits: ColorSchemeFlags,
+}
+
+impl ColorScheme {
+    /// Returns the `normal` value.
+    pub fn normal() -> Self {
+        Self {
+            idents: Default::default(),
+            bits: ColorSchemeFlags::empty(),
+        }
+    }
+}
+
+impl Parse for ColorScheme {
+    fn parse<'i, 't>(_: &ParserContext, input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
+        let mut idents = vec![];
+        let mut bits = ColorSchemeFlags::empty();
+
+        let mut location = input.current_source_location();
+        while let Ok(ident) = input.try_parse(|i| i.expect_ident_cloned()) {
+            let mut is_only = false;
+            match_ignore_ascii_case! { &ident,
+                "normal" => {
+                    if idents.is_empty() && bits.is_empty() {
+                        return Ok(Self::normal());
+                    }
+                    return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+                },
+                "light" => bits.insert(ColorSchemeFlags::LIGHT),
+                "dark" => bits.insert(ColorSchemeFlags::DARK),
+                "only" => {
+                    if bits.intersects(ColorSchemeFlags::ONLY) {
+                        return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+                    }
+                    bits.insert(ColorSchemeFlags::ONLY);
+                    is_only = true;
+                },
+                _ => {},
+            };
+
+            if is_only {
+                if !idents.is_empty() {
+                    // Only is allowed either at the beginning or at the end,
+                    // but not in the middle.
+                    break;
+                }
+            } else {
+                idents.push(CustomIdent::from_ident(location, &ident, &[])?);
+            }
+            location = input.current_source_location();
+        }
+
+        if idents.is_empty() {
+            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+        }
+
+        Ok(Self {
+            idents: crate::ArcSlice::from_iter(idents.into_iter()),
+            bits,
+        })
+    }
+}
+
+impl ToCss for ColorScheme {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        if self.idents.is_empty() {
+            debug_assert!(self.bits.is_empty());
+            return dest.write_str("normal");
+        }
+        let mut first = true;
+        for ident in self.idents.iter() {
+            if !first {
+                dest.write_char(' ')?;
+            }
+            first = false;
+            ident.to_css(dest)?;
+        }
+        if self.bits.intersects(ColorSchemeFlags::ONLY) {
+            dest.write_str(" only")?;
+        }
+        Ok(())
+    }
+}

components/style/values/specified/mod.rs

@@ -42,7 +42,7 @@ pub use self::box_::{Clear, Float, Overflow, OverflowAnchor};
 pub use self::box_::{OverflowClipBox, OverscrollBehavior, Perspective, Resize};
 pub use self::box_::{ScrollSnapAlign, ScrollSnapAxis, ScrollSnapStrictness, ScrollSnapType};
 pub use self::box_::{TouchAction, TransitionProperty, VerticalAlign, WillChange};
-pub use self::color::{Color, ColorOrAuto, ColorPropertyValue};
+pub use self::color::{Color, ColorOrAuto, ColorPropertyValue, ColorScheme};
 pub use self::column::ColumnCount;
 pub use self::counters::{Content, ContentItem, CounterIncrement, CounterSetOrReset};
 pub use self::easing::TimingFunction;