style: Make the -moz-toolbar-prefers-color-scheme a tri-state

This will allow detecting the system theme, which allows fixing some of
the blocked bugs.

Note that when using the system theme we will still match light or dark
appropriately, so this shouldn't change behavior just yet.

Differential Revision: https://phabricator.services.mozilla.com/D113516

components/style/gecko/media_features.rs

@@ -406,18 +406,42 @@ fn eval_prefers_color_scheme(device: &Device, query_value: Option<PrefersColorSc
     }
 }
 
+/// Values for the -moz-toolbar-prefers-color-scheme media feature.
+#[derive(Clone, Copy, Debug, FromPrimitive, Parse, PartialEq, ToCss)]
+#[repr(u8)]
+enum ToolbarPrefersColorScheme {
+    Dark,
+    Light,
+    System,
+}
+
 /// The color-scheme of the toolbar in the current Firefox theme. This is based
 /// on a pref managed by the front-end.
-fn eval_toolbar_prefers_color_scheme(_: &Device, query_value: Option<PrefersColorScheme>) -> bool {
-    let prefers_color_scheme = if static_prefs::pref!("browser.theme.dark-toolbar-theme") {
-        PrefersColorScheme::Dark
-    } else {
-        PrefersColorScheme::Light
+fn eval_toolbar_prefers_color_scheme(d: &Device, query_value: Option<ToolbarPrefersColorScheme>) -> bool {
+    let toolbar_value = match static_prefs::pref!("browser.theme.toolbar-theme") {
+        0 => ToolbarPrefersColorScheme::Dark,
+        1 => ToolbarPrefersColorScheme::Light,
+        _ => ToolbarPrefersColorScheme::System,
     };
 
+    let query_value = match query_value {
+        Some(v) => v,
+        None => return true,
+    };
+
+    if query_value == toolbar_value {
+        return true;
+    }
+
+    if toolbar_value != ToolbarPrefersColorScheme::System {
+        return false;
+    }
+
+    // System might match light and dark as well.
     match query_value {
-        Some(v) => prefers_color_scheme == v,
-        None => true,
+        ToolbarPrefersColorScheme::Dark => eval_prefers_color_scheme(d, Some(PrefersColorScheme::Dark)),
+        ToolbarPrefersColorScheme::Light => eval_prefers_color_scheme(d, Some(PrefersColorScheme::Light)),
+        ToolbarPrefersColorScheme::System => true,
     }
 }
 
@@ -617,7 +641,7 @@ macro_rules! lnf_int_feature {
 /// In order to use them you need to make sure that the pref defined as a static
 /// pref, with `rust: true`. The feature name needs to be defined in
 /// `StaticAtoms.py` just like the others. In order to support dynamic changes,
-/// you also need to add them to kBoolMediaQueryPrefs in nsXPLookAndFeel.cpp
+/// you also need to add them to kMediaQueryPrefs in nsXPLookAndFeel.cpp
 macro_rules! bool_pref_feature {
     ($feature_name:expr, $pref:tt) => {{
         fn __eval(_: &Device, query_value: Option<bool>, _: Option<RangeOrOperator>) -> bool {
@@ -852,7 +876,7 @@ pub static MEDIA_FEATURES: [MediaFeatureDescription; 62] = [
     feature!(
         atom!("-moz-toolbar-prefers-color-scheme"),
         AllowsRanges::No,
-        keyword_evaluator!(eval_toolbar_prefers_color_scheme, PrefersColorScheme),
+        keyword_evaluator!(eval_toolbar_prefers_color_scheme, ToolbarPrefersColorScheme),
         ParsingRequirements::CHROME_AND_UA_ONLY,
     ),