From 22cf429c35b1aea9096775a34cdb04bfbaf57b41 Mon Sep 17 00:00:00 2001
From: Xidorn Quan <me@upsuper.org>
Date: Mon, 9 Apr 2018 19:10:44 +1000
Subject: [PATCH] Use Servo code to check whether a property is inherited.

---
 .../style/properties/properties.mako.rs       |  3 ++-
 ports/geckolib/glue.rs                        | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 8c2376ecf85..39e9b25fa1f 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -826,7 +826,8 @@ impl LonghandId {
         }
     }
 
-    fn inherited(&self) -> bool {
+    /// Returns whether the longhand property is inherited by default.
+    pub fn inherited(&self) -> bool {
         ${static_longhand_id_set("INHERITED", lambda p: p.style_struct.inherited)}
         INHERITED.contains(*self)
     }
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 41905bfe55e..26cf67dc3a8 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -952,6 +952,25 @@ pub unsafe extern "C" fn Servo_Property_IsShorthand(
     prop_id.is_shorthand()
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Property_IsInherited(
+    prop_name: *const nsACString,
+) -> bool {
+    let prop_name = prop_name.as_ref().unwrap().as_str_unchecked();
+    let prop_id = match PropertyId::parse(prop_name) {
+        Ok(id) => id,
+        Err(_) => return false,
+    };
+    let longhand_id = match prop_id {
+        PropertyId::Custom(_) => return true,
+        PropertyId::Longhand(id) |
+        PropertyId::LonghandAlias(id, _) => id,
+        PropertyId::Shorthand(id) |
+        PropertyId::ShorthandAlias(id, _) => id.longhands().next().unwrap(),
+    };
+    longhand_id.inherited()
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_Property_IsAnimatable(property: nsCSSPropertyID) -> bool {
     use style::properties::animated_properties;