From d6750de0c37025330fdac3e7b03d8d789da9e0ff Mon Sep 17 00:00:00 2001
From: Jonathan Kingston <jkt@mozilla.com>
Date: Fri, 15 Feb 2019 21:40:35 +0100
Subject: [PATCH] style: Add support for CSS prefers-color-scheme media
 feature.

Bug: 1494034
Reviewed-by: emilio
---
 components/style/cbindgen.toml           |  1 +
 components/style/gecko/media_features.rs | 28 +++++++++++++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/components/style/cbindgen.toml b/components/style/cbindgen.toml
index 1a736eb1be9..50696b32e6d 100644
--- a/components/style/cbindgen.toml
+++ b/components/style/cbindgen.toml
@@ -57,6 +57,7 @@ include = [
   "CursorKind",
   "Display",
   "DisplayMode",
+  "PrefersColorScheme",
   "ExtremumLength",
   "FillRule",
   "FontDisplay",
diff --git a/components/style/gecko/media_features.rs b/components/style/gecko/media_features.rs
index b6596c75de8..24f2009a3a8 100644
--- a/components/style/gecko/media_features.rs
+++ b/components/style/gecko/media_features.rs
@@ -280,6 +280,16 @@ enum PrefersReducedMotion {
     Reduce,
 }
 
+/// Values for the prefers-color-scheme media feature.
+#[derive(Clone, Copy, Debug, FromPrimitive, Parse, PartialEq, ToCss)]
+#[repr(u8)]
+#[allow(missing_docs)]
+pub enum PrefersColorScheme {
+    Light,
+    Dark,
+    NoPreference,
+}
+
 /// https://drafts.csswg.org/mediaqueries-5/#prefers-reduced-motion
 fn eval_prefers_reduced_motion(device: &Device, query_value: Option<PrefersReducedMotion>) -> bool {
     let prefers_reduced =
@@ -348,6 +358,16 @@ fn eval_overflow_inline(device: &Device, query_value: Option<OverflowInline>) ->
     }
 }
 
+/// https://drafts.csswg.org/mediaqueries-5/#prefers-color-scheme
+fn eval_prefers_color_scheme(device: &Device, query_value: Option<PrefersColorScheme>) -> bool {
+    let prefers_color_scheme =
+        unsafe { bindings::Gecko_MediaFeatures_PrefersColorScheme(device.document()) };
+    match query_value {
+        Some(v) => prefers_color_scheme == v,
+        None => prefers_color_scheme != PrefersColorScheme::NoPreference,
+    }
+}
+
 /// https://drafts.csswg.org/mediaqueries-4/#mf-interaction
 bitflags! {
     struct PointerCapabilities: u8 {
@@ -526,7 +546,7 @@ lazy_static! {
     /// to support new types in these entries and (2) ensuring that either
     /// nsPresContext::MediaFeatureValuesChanged is called when the value that
     /// would be returned by the evaluator function could change.
-    pub static ref MEDIA_FEATURES: [MediaFeatureDescription; 52] = [
+    pub static ref MEDIA_FEATURES: [MediaFeatureDescription; 53] = [
         feature!(
             atom!("width"),
             AllowsRanges::Yes,
@@ -657,6 +677,12 @@ lazy_static! {
             keyword_evaluator!(eval_overflow_inline, OverflowInline),
             ParsingRequirements::empty(),
         ),
+        feature!(
+            atom!("prefers-color-scheme"),
+            AllowsRanges::No,
+            keyword_evaluator!(eval_prefers_color_scheme, PrefersColorScheme),
+            ParsingRequirements::empty(),
+        ),
         feature!(
             atom!("pointer"),
             AllowsRanges::No,