From 34373c2ac81131ec9aa8681adc7d546d9e3efc0c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20Cobos=20=C3=81lvarez?= <emilio@crisal.io>
Date: Mon, 20 Jun 2022 14:07:12 +0000
Subject: [PATCH] style: Check for allowed colors recursively in forced-colors
 mode

Differential Revision: https://phabricator.services.mozilla.com/D149733
---
 components/style/properties/cascade.rs     | 21 +++++++++------------
 components/style/values/specified/color.rs | 21 +++++++++++----------
 2 files changed, 20 insertions(+), 22 deletions(-)

diff --git a/components/style/properties/cascade.rs b/components/style/properties/cascade.rs
index 3d3c6b833b8..a85d507bd18 100644
--- a/components/style/properties/cascade.rs
+++ b/components/style/properties/cascade.rs
@@ -425,13 +425,7 @@ fn tweak_when_ignoring_colors(
     // A few special-cases ahead.
     match **declaration {
         PropertyDeclaration::BackgroundColor(ref color) => {
-            // We honor system colors.
-            if color.is_system() {
-                return;
-            }
-            // For background-color, we revert or initial-with-preserved-alpha
-            // otherwise, this is needed to preserve semi-transparent
-            // backgrounds.
+            // We honor system colors and transparent colors unconditionally.
             //
             // NOTE(emilio): We honor transparent unconditionally, like we do
             // for color, even though it causes issues like bug 1625036. The
@@ -440,6 +434,12 @@ fn tweak_when_ignoring_colors(
             // broken in other applications as well, and not honoring
             // transparent makes stuff uglier or break unconditionally
             // (bug 1666059, bug 1755713).
+            if color.honored_in_forced_colors_mode(/* allow_transparent = */ true) {
+                return;
+            }
+            // For background-color, we revert or initial-with-preserved-alpha
+            // otherwise, this is needed to preserve semi-transparent
+            // backgrounds.
             let alpha = alpha_channel(color, context);
             if alpha == 0 {
                 return;
@@ -451,10 +451,7 @@ fn tweak_when_ignoring_colors(
         },
         PropertyDeclaration::Color(ref color) => {
             // We honor color: transparent and system colors.
-            if color.0.is_system() {
-                return;
-            }
-            if alpha_channel(&color.0, context) == 0 {
+            if color.0.honored_in_forced_colors_mode(/* allow_transparent = */ true) {
                 return;
             }
             // If the inherited color would be transparent, but we would
@@ -491,7 +488,7 @@ fn tweak_when_ignoring_colors(
             // caret-color doesn't make sense (using currentColor is fine), and
             // we ignore accent-color in high-contrast-mode anyways.
             if let Some(color) = declaration.color_value() {
-                if color.is_system() {
+                if color.honored_in_forced_colors_mode(/* allow_transparent = */ false) {
                     return;
                 }
             }
diff --git a/components/style/values/specified/color.rs b/components/style/values/specified/color.rs
index 6a285a265d5..e29f3558e6a 100644
--- a/components/style/values/specified/color.rs
+++ b/components/style/values/specified/color.rs
@@ -515,16 +515,17 @@ fn parse_hash_color(value: &[u8]) -> Result<RGBA, ()> {
 }
 
 impl Color {
-    /// Returns whether this color is a system color.
-    #[cfg(feature = "gecko")]
-    pub fn is_system(&self) -> bool {
-        matches!(self, Color::System(..))
-    }
-
-    /// Returns whether this color is a system color.
-    #[cfg(feature = "servo")]
-    pub fn is_system(&self) -> bool {
-        false
+    /// Returns whether this color is allowed in forced-colors mode.
+    pub fn honored_in_forced_colors_mode(&self, allow_transparent: bool) -> bool {
+        match *self {
+            Color::InheritFromBodyQuirk | Color::CurrentColor => false,
+            Color::System(..) => true,
+            Color::Numeric { ref parsed, .. } => allow_transparent && parsed.alpha == 0,
+            Color::ColorMix(ref mix) => {
+                mix.left.honored_in_forced_colors_mode(allow_transparent) &&
+                    mix.right.honored_in_forced_colors_mode(allow_transparent)
+            },
+        }
     }
 
     /// Returns currentcolor value.