Bug 1966890 - Factor out the light-dark() function. r=dshin

Remove the light-dark() pref while at it.

Differential Revision: https://phabricator.services.mozilla.com/D249787

modules/libpref/init/StaticPrefList.yaml

@@ -9751,13 +9751,6 @@
   mirror: always
   rust: true
 
-# Is support for light-dark() on content enabled?
-- name: layout.css.light-dark.enabled
-  type: RelaxedAtomicBool
-  value: true
-  mirror: always
-  rust: true
-
 # Is support for fit-content() enabled?
 - name: layout.css.fit-content-function.enabled
   type: RelaxedAtomicBool

servo/components/style/values/generics/color.rs

@@ -5,7 +5,8 @@
 //! Generic types for color properties.
 
 use crate::color::{mix::ColorInterpolationMethod, AbsoluteColor, ColorFunction};
-use crate::values::specified::percentage::ToPercentage;
+use crate::parser::ParserContext;
+use crate::values::{specified::percentage::ToPercentage, computed::ToComputedValue, Parser, ParseError};
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
 
@@ -208,3 +209,45 @@ impl<C> GenericCaretColor<C> {
 }
 
 pub use self::GenericCaretColor as CaretColor;
+
+/// A light-dark(<light>, <dark>) function.
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToShmem, ToCss)]
+#[css(function, comma)]
+#[repr(C)]
+pub struct GenericLightDark<T> {
+    /// The value returned when using a light theme.
+    pub light: T,
+    /// The value returned when using a dark theme.
+    pub dark: T,
+}
+
+impl<T> GenericLightDark<T> {
+    /// Parse the light-dark() function.
+    pub fn parse_with<'i>(
+        context: &ParserContext,
+        input: &mut Parser<'i, '_>,
+        mut parse_one: impl FnMut(&ParserContext, &mut Parser<'i, '_>) -> Result<T, ParseError<'i>>,
+    ) -> Result<Self, ParseError<'i>> {
+        input.expect_function_matching("light-dark")?;
+        input.parse_nested_block(|input| {
+            let light = parse_one(context, input)?;
+            input.expect_comma()?;
+            let dark = parse_one(context, input)?;
+            Ok(Self { light, dark })
+        })
+    }
+}
+
+impl<T: ToComputedValue> GenericLightDark<T> {
+    /// Choose the light or dark version of this value for computation purposes, and compute it.
+    pub fn compute(&self, cx: &crate::values::computed::Context) -> T::ComputedValue {
+        let dark = cx.device().is_dark_color_scheme(cx.builder.color_scheme);
+        if cx.for_non_inherited_property {
+            cx.rule_cache_conditions
+                .borrow_mut()
+                .set_color_scheme_dependency(cx.builder.color_scheme);
+        }
+        let chosen = if dark { &self.dark } else { &self.light };
+        chosen.to_computed_value(cx)
+    }
+}

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

@@ -11,7 +11,7 @@ use crate::media_queries::Device;
 use crate::parser::{Parse, ParserContext};
 use crate::values::computed::{Color as ComputedColor, Context, ToComputedValue};
 use crate::values::generics::color::{
-    ColorMixFlags, GenericCaretColor, GenericColorMix, GenericColorOrAuto,
+    ColorMixFlags, GenericCaretColor, GenericColorMix, GenericColorOrAuto, GenericLightDark
 };
 use crate::values::specified::Percentage;
 use crate::values::{normalize, CustomIdent};
@@ -124,54 +124,12 @@ pub enum Color {
     /// A color mix.
     ColorMix(Box<ColorMix>),
     /// A light-dark() color.
-    LightDark(Box<LightDark>),
+    LightDark(Box<GenericLightDark<Self>>),
     /// Quirksmode-only rule for inheriting color from the body
     #[cfg(feature = "gecko")]
     InheritFromBodyQuirk,
 }
 
-/// A light-dark(<light-color>, <dark-color>) function.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToShmem, ToCss)]
-#[css(function, comma)]
-pub struct LightDark {
-    /// The <color> that is returned when using a light theme.
-    pub light: Color,
-    /// The <color> that is returned when using a dark theme.
-    pub dark: Color,
-}
-
-impl LightDark {
-    fn compute(&self, cx: &Context) -> ComputedColor {
-        let dark = cx.device().is_dark_color_scheme(cx.builder.color_scheme);
-        if cx.for_non_inherited_property {
-            cx.rule_cache_conditions
-                .borrow_mut()
-                .set_color_scheme_dependency(cx.builder.color_scheme);
-        }
-        let used = if dark { &self.dark } else { &self.light };
-        used.to_computed_value(cx)
-    }
-
-    fn parse<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-        preserve_authored: PreserveAuthored,
-    ) -> Result<Self, ParseError<'i>> {
-        let enabled =
-            context.chrome_rules_enabled() || static_prefs::pref!("layout.css.light-dark.enabled");
-        if !enabled {
-            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-        }
-        input.expect_function_matching("light-dark")?;
-        input.parse_nested_block(|input| {
-            let light = Color::parse_internal(context, input, preserve_authored)?;
-            input.expect_comma()?;
-            let dark = Color::parse_internal(context, input, preserve_authored)?;
-            Ok(LightDark { light, dark })
-        })
-    }
-}
-
 impl From<AbsoluteColor> for Color {
     #[inline]
     fn from(value: AbsoluteColor) -> Self {
@@ -483,7 +441,7 @@ impl Color {
                     return Ok(Color::ColorMix(Box::new(mix)));
                 }
 
-                if let Ok(ld) = input.try_parse(|i| LightDark::parse(context, i, preserve_authored))
+                if let Ok(ld) = input.try_parse(|i| GenericLightDark::parse_with(context, i, |context, i| Self::parse_internal(context, i, preserve_authored)))
                 {
                     return Ok(Color::LightDark(Box::new(ld)));
                 }