servo: Merge #18008 - stylo: Avoid reporting rules that contain both normal and important declarations twice (from emilio:double-important); r=upsuper

Bug: 1387906
Source-Repo: https://github.com/servo/servo
Source-Revision: 4fdc571e9fa4e95ec7a5ce7bfd03db6b544b8c9e

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 0474e60faf024161af94689d7d77233e55947605

servo/ports/geckolib/glue.rs

@@ -1823,13 +1823,34 @@ pub extern "C" fn Servo_ComputedValues_EqualCustomProperties(
 #[no_mangle]
 pub extern "C" fn Servo_ComputedValues_GetStyleRuleList(values: ServoStyleContextBorrowed,
                                                         rules: RawGeckoServoStyleRuleListBorrowedMut) {
-    if let Some(ref rule_node) = values.rules {
+    let rule_node = match values.rules {
+        Some(ref r) => r,
+        None => return,
+    };
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+
+    // TODO(emilio): Will benefit from SmallVec.
     let mut result = vec![];
     for node in rule_node.self_and_ancestors() {
-            if let &StyleSource::Style(ref rule) = node.style_source() {
-                result.push(rule);
+        let style_rule = match *node.style_source() {
+            StyleSource::Style(ref rule) => rule,
+            _ => continue,
+        };
+
+        if node.importance().important() {
+            let block = style_rule.read_with(&guard).block.read_with(&guard);
+            if block.any_normal() {
+                // We'll append it when we find the normal rules in our
+                // parent chain.
+                continue;
             }
         }
+
+        result.push(style_rule);
+    }
+
     unsafe { rules.set_len(result.len() as u32) };
     for (ref src, ref mut dest) in result.into_iter().zip(rules.iter_mut()) {
         src.with_raw_offset_arc(|arc| {
@@ -1837,7 +1858,6 @@ pub extern "C" fn Servo_ComputedValues_GetStyleRuleList(values: ServoStyleContex
         })
     }
 }
-}
 
 /// See the comment in `Device` to see why it's ok to pass an owned reference to
 /// the pres context (hint: the context outlives the StyleSet, that holds the