stylo: Implement font-language-override descriptor for @font-face rule

components/style/font_face.rs

@@ -17,6 +17,8 @@ use error_reporting::ContextualParseError;
 #[cfg(feature = "gecko")] use gecko_bindings::structs::CSSFontFaceDescriptors;
 #[cfg(feature = "gecko")] use cssparser::UnicodeRange;
 use parser::{ParserContext, log_css_error, Parse};
+#[cfg(feature = "gecko")]
+use properties::longhands::font_language_override;
 use selectors::parser::SelectorParseError;
 use shared_lock::{SharedRwLockReadGuard, ToCssWithGuard};
 use std::fmt;
@@ -407,7 +409,10 @@ font_face_descriptors! {
             font_feature_settings::T::Normal
         },
 
-        // FIXME: add font-language-override.
+        /// The language override of this font face.
+        "font-language-override" language_override / mFontLanguageOverride: font_language_override::SpecifiedValue = {
+            font_language_override::SpecifiedValue::Normal
+        },
     ]
 }
 

components/style/gecko/rules.rs

@@ -15,6 +15,7 @@ use gecko_bindings::structs::{self, nsCSSFontFaceRule, nsCSSValue};
 use gecko_bindings::structs::{nsCSSCounterDesc, nsCSSCounterStyleRule};
 use gecko_bindings::sugar::ns_css_value::ToNsCssValue;
 use gecko_bindings::sugar::refptr::{RefPtr, UniqueRefPtr};
+use properties::longhands::font_language_override;
 use shared_lock::{ToCssWithGuard, SharedRwLockReadGuard};
 use std::{fmt, str};
 use values::generics::FontSettings;
@@ -67,6 +68,17 @@ impl ToNsCssValue for font_feature_settings::T {
     }
 }
 
+impl ToNsCssValue for font_language_override::SpecifiedValue {
+    fn convert(self, nscssvalue: &mut nsCSSValue) {
+        match self {
+            font_language_override::SpecifiedValue::Normal => nscssvalue.set_normal(),
+            font_language_override::SpecifiedValue::Override(ref lang) => nscssvalue.set_string(&*lang),
+            // This path is unreachable because the descriptor is only specified by the user.
+            font_language_override::SpecifiedValue::System(_) => unreachable!(),
+        }
+    }
+}
+
 macro_rules! map_enum {
     (
         $(

components/style/properties/longhand/font.mako.rs

@@ -2012,7 +2012,7 @@ https://drafts.csswg.org/css-fonts-4/#low-level-font-variation-settings-control-
         // OpenType "language system" tag, so we should be able to compute
         // it and store it as a 32-bit integer
         // (see http://www.microsoft.com/typography/otspec/languagetags.htm).
-        #[derive(PartialEq, Clone, Copy, Debug)]
+        #[derive(Clone, Copy, Debug, PartialEq, Eq)]
         #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
         pub struct T(pub u32);
     }
@@ -2082,6 +2082,14 @@ https://drafts.csswg.org/css-fonts-4/#low-level-font-variation-settings-control-
         }
     }
 
+    /// Used in @font-face.
+    impl Parse for SpecifiedValue {
+        fn parse<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>)
+                         -> Result<Self, ParseError<'i>> {
+            parse(context, input)
+        }
+    }
+
     #[cfg(feature = "gecko")]
     impl From<u32> for computed_value::T {
         fn from(bits: u32) -> computed_value::T {