From 0307500c3d1bd9bf7042a78df31188d45c8c1768 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20Cobos=20=C3=81lvarez?= <emilio@crisal.io>
Date: Tue, 6 Jun 2023 23:37:35 +0200
Subject: [PATCH] style: Choose tabpanel background based on content preferred
 color-scheme

If the theme is dark but user prefers light pages, the background of the
tabpanel should arguably be light, since it can be seen across some
navigations.

Expose a -moz-content-prefers-color-scheme media query to chrome pages
so that our UI can correctly query it (and remove the unused -moz-proton
atom while at it).

Differential Revision: https://phabricator.services.mozilla.com/D136437
---
 components/style/gecko/media_features.rs | 32 +++++++++++++++++++++---
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/components/style/gecko/media_features.rs b/components/style/gecko/media_features.rs
index c80ace2015b..66722af6c72 100644
--- a/components/style/gecko/media_features.rs
+++ b/components/style/gecko/media_features.rs
@@ -396,16 +396,31 @@ 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 {
+fn do_eval_prefers_color_scheme(
+    device: &Device,
+    use_content: bool,
+    query_value: Option<PrefersColorScheme>,
+) -> bool {
     let prefers_color_scheme =
-        unsafe { bindings::Gecko_MediaFeatures_PrefersColorScheme(device.document()) };
+        unsafe { bindings::Gecko_MediaFeatures_PrefersColorScheme(device.document(), use_content) };
     match query_value {
         Some(v) => prefers_color_scheme == v,
         None => true,
     }
 }
 
+/// https://drafts.csswg.org/mediaqueries-5/#prefers-color-scheme
+fn eval_prefers_color_scheme(device: &Device, query_value: Option<PrefersColorScheme>) -> bool {
+    do_eval_prefers_color_scheme(device, /* use_content = */ false, query_value)
+}
+
+fn eval_content_prefers_color_scheme(
+    device: &Device,
+    query_value: Option<PrefersColorScheme>,
+) -> bool {
+    do_eval_prefers_color_scheme(device, /* use_content = */ true, query_value)
+}
+
 bitflags! {
     /// https://drafts.csswg.org/mediaqueries-4/#mf-interaction
     struct PointerCapabilities: u8 {
@@ -652,7 +667,7 @@ macro_rules! bool_pref_feature {
 /// 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 MEDIA_FEATURES: [MediaFeatureDescription; 57] = [
+pub static MEDIA_FEATURES: [MediaFeatureDescription; 58] = [
     feature!(
         atom!("width"),
         AllowsRanges::Yes,
@@ -805,6 +820,15 @@ pub static MEDIA_FEATURES: [MediaFeatureDescription; 57] = [
         keyword_evaluator!(eval_prefers_color_scheme, PrefersColorScheme),
         ParsingRequirements::empty(),
     ),
+    // Evaluates to the preferred color scheme for content. Only useful in
+    // chrome context, where the chrome color-scheme and the content
+    // color-scheme might differ.
+    feature!(
+        atom!("-moz-content-prefers-color-scheme"),
+        AllowsRanges::No,
+        keyword_evaluator!(eval_content_prefers_color_scheme, PrefersColorScheme),
+        ParsingRequirements::CHROME_AND_UA_ONLY,
+    ),
     feature!(
         atom!("pointer"),
         AllowsRanges::No,