stylo: Bug 1355345 - Support font-display descriptor in @font-face rule

2 files changed, 28 insertions, 2 deletions

diff --git a/components/style/font_face.rs b/components/style/font_face.rs
index 4eb79690c91..4c953c3b028 100644
--- a/components/style/font_face.rs
+++ b/components/style/font_face.rs
@@ -72,6 +72,17 @@ impl ToCss for UrlSource {
     }
 }
 
+/// A font-display value for a @font-face rule.
+/// The font-display descriptor determines how a font face is displayed based
+/// on whether and when it is downloaded and ready to use.
+define_css_keyword_enum!(FontDisplay:
+                         "auto" => Auto,
+                         "block" => Block,
+                         "swap" => Swap,
+                         "fallback" => Fallback,
+                         "optional" => Optional);
+add_impls_for_keyword_enum!(FontDisplay);
+
 /// Parse the block inside a `@font-face` rule.
 ///
 /// Note that the prelude parsing code lives in the `stylesheets` module.
@@ -332,6 +343,9 @@ font_face_descriptors! {
         /// The stretch of this font face
         "font-stretch" stretch / mStretch: font_stretch::T = font_stretch::T::normal,
 
+        /// The display of this font face
+        "font-display" display / mDisplay: FontDisplay = FontDisplay::Auto,
+
         /// The ranges of code points outside of which this font face should not be used.
         "unicode-range" unicode_range / mUnicodeRange: Vec<UnicodeRange> = vec![
             UnicodeRange { start: 0, end: 0x10FFFF }
@@ -342,7 +356,7 @@ font_face_descriptors! {
             font_feature_settings::T::Normal
         },
 
-        // FIXME: add font-language-override, and font-display.
+        // FIXME: add font-language-override.
     ]
 }
 
diff --git a/components/style/gecko/rules.rs b/components/style/gecko/rules.rs
index aceb4aec5e9..80aa7a7acb2 100644
--- a/components/style/gecko/rules.rs
+++ b/components/style/gecko/rules.rs
@@ -9,7 +9,7 @@ use computed_values::{font_feature_settings, font_stretch, font_style, font_weig
 use computed_values::font_family::FamilyName;
 use counter_style;
 use cssparser::UnicodeRange;
-use font_face::{FontFaceRuleData, Source};
+use font_face::{FontFaceRuleData, Source, FontDisplay};
 use gecko_bindings::bindings;
 use gecko_bindings::structs::{self, nsCSSFontFaceRule, nsCSSValue};
 use gecko_bindings::structs::{nsCSSCounterDesc, nsCSSCounterStyleRule};
@@ -137,6 +137,18 @@ impl ToNsCssValue for Vec<UnicodeRange> {
     }
 }
 
+impl ToNsCssValue for FontDisplay {
+    fn convert(self, nscssvalue: &mut nsCSSValue) {
+        nscssvalue.set_enum(match self {
+            FontDisplay::Auto => structs::NS_FONT_DISPLAY_AUTO,
+            FontDisplay::Block => structs::NS_FONT_DISPLAY_BLOCK,
+            FontDisplay::Swap => structs::NS_FONT_DISPLAY_SWAP,
+            FontDisplay::Fallback => structs::NS_FONT_DISPLAY_FALLBACK,
+            FontDisplay::Optional => structs::NS_FONT_DISPLAY_OPTIONAL,
+        } as i32)
+    }
+}
+
 impl From<FontFaceRuleData> for FontFaceRule {
     fn from(data: FontFaceRuleData) -> FontFaceRule {
         let mut result = unsafe {