From 71dbc6c023320d29ae591e6010ece33b6e9c8d82 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20Cobos=20=C3=81lvarez?= <emilio@crisal.io>
Date: Sat, 20 May 2017 11:56:48 +0200
Subject: [PATCH] Bug 1366427: Make backdrop not inherit from the parent
 element. r=heycam
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MozReview-Commit-ID: EnnmvDsgbdx
Signed-off-by: Emilio Cobos Álvarez <emilio@crisal.io>
---
 components/style/gecko/pseudo_element.rs | 9 +++++++++
 components/style/stylist.rs              | 6 +++---
 ports/geckolib/glue.rs                   | 6 +++++-
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/components/style/gecko/pseudo_element.rs b/components/style/gecko/pseudo_element.rs
index b15e17e6f38..93da2b589d0 100644
--- a/components/style/gecko/pseudo_element.rs
+++ b/components/style/gecko/pseudo_element.rs
@@ -49,6 +49,15 @@ impl PseudoElement {
         PseudoElementCascadeType::Lazy
     }
 
+    /// Whether the pseudo-element should inherit from the default computed
+    /// values instead of from the parent element.
+    ///
+    /// This is not the common thing, but there are some pseudos (namely:
+    /// ::backdrop), that shouldn't inherit from the parent element.
+    pub fn inherits_from_default_values(&self) -> bool {
+        !matches!(*self, PseudoElement::Backdrop)
+    }
+
     /// Gets the canonical index of this eagerly-cascaded pseudo-element.
     #[inline]
     pub fn eager_index(&self) -> usize {
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index a2f358b3f22..f1c541b8ef1 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -630,7 +630,7 @@ impl Stylist {
                                                   guards: &StylesheetGuards,
                                                   element: &E,
                                                   pseudo: &PseudoElement,
-                                                  parent: &Arc<ComputedValues>,
+                                                  parent_style: &ComputedValues,
                                                   font_metrics: &FontMetricsProvider)
                                                   -> Option<ComputedStyle>
         where E: TElement,
@@ -649,8 +649,8 @@ impl Stylist {
             properties::cascade(&self.device,
                                 &rule_node,
                                 guards,
-                                Some(&**parent),
-                                Some(&**parent),
+                                Some(parent_style),
+                                Some(parent_style),
                                 None,
                                 &RustLogReporter,
                                 font_metrics,
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 55c031351c8..362c5804427 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -1205,7 +1205,11 @@ fn get_pseudo_style(guard: &SharedRwLockReadGuard,
         PseudoElementCascadeType::Precomputed => unreachable!("No anonymous boxes"),
         PseudoElementCascadeType::Lazy => {
             let d = doc_data.borrow_mut();
-            let base = styles.primary.values();
+            let base = if pseudo.inherits_from_default_values() {
+                d.default_computed_values()
+            } else {
+                styles.primary.values()
+            };
             let guards = StylesheetGuards::same(guard);
             let metrics = get_metrics_provider_for_product();
             d.stylist.lazily_compute_pseudo_element_style(&guards,