Bug 1891700 - Accept color-mix() in font palette override colors, provided the components used are absolute colors. r=tlouw

Differential Revision: https://phabricator.services.mozilla.com/D208115

servo/components/style/stylesheets/font_palette_values_rule.rs

@@ -44,12 +44,17 @@ impl Parse for FontPaletteOverrideColor {
         let index = NonNegativeInteger::parse(context, input)?;
         let location = input.current_source_location();
         let color = SpecifiedColor::parse(context, input)?;
-        // Only absolute colors are accepted here.
-        if let SpecifiedColor::Absolute { .. } = color {
-            Ok(FontPaletteOverrideColor { index, color })
-        } else {
-            Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+        // Only absolute colors are accepted here:
+        //   https://drafts.csswg.org/css-fonts/#override-color
+        //   https://drafts.csswg.org/css-color-5/#absolute-color
+        // so check that the specified color can be resolved without a context
+        // or currentColor value.
+        if color.resolve_to_absolute().is_some() {
+            // We store the specified color (not the resolved absolute color)
+            // because that is what the rule exposes to authors.
+            return Ok(FontPaletteOverrideColor { index, color });
         }
+        Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError))
     }
 }
 
@@ -178,14 +183,15 @@ impl FontPaletteValuesRule {
                 }
             }
             for c in &self.override_colors {
-                if let SpecifiedColor::Absolute(ref absolute) = c.color {
-                    unsafe {
-                        Gecko_SetFontPaletteOverride(
-                            palette_values,
-                            c.index.0.value(),
-                            (&absolute.color) as *const _ as *mut _,
-                        );
-                    }
+                // We checked at parse time that the specified color can be resolved
+                // in this way, so the unwrap() here will succeed.
+                let absolute = c.color.resolve_to_absolute().unwrap();
+                unsafe {
+                    Gecko_SetFontPaletteOverride(
+                        palette_values,
+                        c.index.0.value(),
+                        (&absolute) as *const _ as *mut _,
+                    );
                 }
             }
         }

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

@@ -607,6 +607,35 @@ impl Color {
         }))
     }
 
+    /// Resolve this Color into an AbsoluteColor if it does not use any of the
+    /// forms that are invalid in an absolute color.
+    ///   https://drafts.csswg.org/css-color-5/#absolute-color
+    /// Returns None if the specified color is not valid as an absolute color.
+    pub fn resolve_to_absolute(&self) -> Option<AbsoluteColor> {
+        use crate::values::specified::percentage::ToPercentage;
+
+        match self {
+            Self::Absolute(c) => return Some(c.color),
+            Self::ColorMix(ref mix) => {
+                if let Some(left) = mix.left.resolve_to_absolute() {
+                    if let Some(right) = mix.right.resolve_to_absolute() {
+                        return Some(crate::color::mix::mix(
+                            mix.interpolation,
+                            &left,
+                            mix.left_percentage.to_percentage(),
+                            &right,
+                            mix.right_percentage.to_percentage(),
+                            mix.flags,
+                        ))
+                    }
+                }
+            },
+            _ => (),
+        };
+
+        None
+    }
+
     /// Parse a color, with quirks.
     ///
     /// <https://quirks.spec.whatwg.org/#the-hashless-hex-color-quirk>

testing/web-platform/meta/css/css-fonts/parsing/font-palette-values-invalid.html.ini

@@ -1,3 +0,0 @@
-[font-palette-values-invalid.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]

testing/web-platform/meta/css/css-fonts/parsing/font-palette-values-valid.html.ini

@@ -1,5 +0,0 @@
-[font-palette-values-valid.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
-  [CSS Fonts Module Level 4: parsing @font-palette-values 33]
-    expected: FAIL