From d89816bb5fa90421a4dea49ff6387f635ce7b389 Mon Sep 17 00:00:00 2001
From: Bobby Holley <bobbyholley@gmail.com>
Date: Wed, 4 Nov 2015 18:15:30 -0800
Subject: [PATCH] Consider all the pseudo-classes in a given compound selector
 when computing restyle hints, not just the rightmost one.

For some reason when I wrote this code I mixed up the rules for pseudo-elements
(rightmost, maximum of one) with those of pseudo-classes (which have no such
restriction). This caused a correctness issue which can be demonstrated with the
associated reftest modification.
---
 components/style/restyle_hints.rs             | 19 ++++++++++---------
 .../mozilla/tests/css/restyle_hints_state.css |  8 ++++++--
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/components/style/restyle_hints.rs b/components/style/restyle_hints.rs
index acb521b0f10..fe143c3e315 100644
--- a/components/style/restyle_hints.rs
+++ b/components/style/restyle_hints.rs
@@ -220,15 +220,16 @@ impl StateDependencySet {
         let mut cur = selector;
         let mut combinator: Option<Combinator> = None;
         loop {
-            if let Some(rightmost) = cur.simple_selectors.last() {
-                let state_dep = selector_to_state(rightmost);
-                if !state_dep.is_empty() {
-                    self.deps.push(StateDependency {
-                        selector: cur.clone(),
-                        combinator: combinator,
-                        state: state_dep,
-                    });
-                }
+            let mut deps = ElementState::empty();
+            for s in &cur.simple_selectors {
+                deps.insert(selector_to_state(s));
+            }
+            if !deps.is_empty() {
+                self.deps.push(StateDependency {
+                    selector: cur.clone(),
+                    combinator: combinator,
+                    state: deps,
+                });
             }
 
             cur = match cur.next {
diff --git a/tests/wpt/mozilla/tests/css/restyle_hints_state.css b/tests/wpt/mozilla/tests/css/restyle_hints_state.css
index 673ac25d572..6a152778e42 100644
--- a/tests/wpt/mozilla/tests/css/restyle_hints_state.css
+++ b/tests/wpt/mozilla/tests/css/restyle_hints_state.css
@@ -19,11 +19,15 @@ fieldset:enabled div {
 fieldset:enabled > div {
   background-color: yellow;
 }
-fieldset:enabled ~ div {
+
+/* Add an unnecessary :first-child to make sure that restyle hints see
+ * non-rightmost pseudo-selectors.
+ * */
+fieldset:enabled:first-child ~ div {
   color: pink;
   background-color: purple;
 }
-fieldset:enabled + div {
+fieldset:enabled:first-child + div {
   color: brown;
   background-color: orange;
 }