From 74a46d96ebe786ceaab0a6b2189a11e4e2632015 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20Cobos=20=C3=81lvarez?= <emilio@crisal.io>
Date: Mon, 21 Sep 2020 11:05:51 +0000
Subject: [PATCH] style: Don't optimize ::before/::after away if
 content/display have been specified via custom properties.

We need to treat them the same way as we treat content: inherit.

Differential Revision: https://phabricator.services.mozilla.com/D90222
---
 components/style/properties/cascade.rs        | 19 +++++++++++++++++++
 .../style/properties/computed_value_flags.rs  |  8 ++++----
 .../style/properties/properties.mako.rs       |  4 ++--
 components/style/style_resolver.rs            |  4 ++--
 4 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/components/style/properties/cascade.rs b/components/style/properties/cascade.rs
index 11f3beb2481..e161e2690d2 100644
--- a/components/style/properties/cascade.rs
+++ b/components/style/properties/cascade.rs
@@ -478,6 +478,25 @@ impl<'a, 'b: 'a> Cascade<'a, 'b> {
                 .rule_cache_conditions
                 .borrow_mut()
                 .set_uncacheable();
+
+            // NOTE(emilio): We only really need to add the `display` /
+            // `content` flag if the CSS variable has not been specified on our
+            // declarations, but we don't have that information at this point,
+            // and it doesn't seem like an important enough optimization to
+            // warrant it.
+            match declaration.id {
+                LonghandId::Display => {
+                    self.context
+                        .builder
+                        .add_flags(ComputedValueFlags::DISPLAY_DEPENDS_ON_INHERITED_STYLE);
+                },
+                LonghandId::Content => {
+                    self.context
+                        .builder
+                        .add_flags(ComputedValueFlags::CONTENT_DEPENDS_ON_INHERITED_STYLE);
+                },
+                _ => {},
+            }
         }
 
         Cow::Owned(declaration.value.substitute_variables(
diff --git a/components/style/properties/computed_value_flags.rs b/components/style/properties/computed_value_flags.rs
index 221363ba4b1..dc9597e087b 100644
--- a/components/style/properties/computed_value_flags.rs
+++ b/components/style/properties/computed_value_flags.rs
@@ -42,17 +42,17 @@ bitflags! {
         /// A flag used to mark styles which are a pseudo-element or under one.
         const IS_IN_PSEUDO_ELEMENT_SUBTREE = 1 << 4;
 
-        /// Whether this style inherits the `display` property.
+        /// Whether this style's `display` property depends on our parent style.
         ///
         /// This is important because it may affect our optimizations to avoid
         /// computing the style of pseudo-elements, given whether the
         /// pseudo-element is generated depends on the `display` value.
-        const INHERITS_DISPLAY = 1 << 6;
+        const DISPLAY_DEPENDS_ON_INHERITED_STYLE = 1 << 6;
 
-        /// Whether this style inherits the `content` property.
+        /// Whether this style's `content` depends on our parent style.
         ///
         /// Important because of the same reason.
-        const INHERITS_CONTENT = 1 << 7;
+        const CONTENT_DEPENDS_ON_INHERITED_STYLE = 1 << 7;
 
         /// Whether the child explicitly inherits any reset property.
         const INHERITS_RESET_STYLE = 1 << 8;
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index f98df39a629..0198d7cdb9b 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -3646,11 +3646,11 @@ impl<'a> StyleBuilder<'a> {
         self.add_flags(ComputedValueFlags::INHERITS_RESET_STYLE);
 
         % if property.ident == "content":
-        self.add_flags(ComputedValueFlags::INHERITS_CONTENT);
+        self.add_flags(ComputedValueFlags::CONTENT_DEPENDS_ON_INHERITED_STYLE);
         % endif
 
         % if property.ident == "display":
-        self.add_flags(ComputedValueFlags::INHERITS_DISPLAY);
+        self.add_flags(ComputedValueFlags::DISPLAY_DEPENDS_ON_INHERITED_STYLE);
         % endif
 
         if self.${property.style_struct.ident}.ptr_eq(inherited_struct) {
diff --git a/components/style/style_resolver.rs b/components/style/style_resolver.rs
index 8caf3cec4c3..70ac1b3b4d3 100644
--- a/components/style/style_resolver.rs
+++ b/components/style/style_resolver.rs
@@ -139,13 +139,13 @@ fn eager_pseudo_is_definitely_not_generated(
         return false;
     }
 
-    if !style.flags.intersects(ComputedValueFlags::INHERITS_DISPLAY) &&
+    if !style.flags.intersects(ComputedValueFlags::DISPLAY_DEPENDS_ON_INHERITED_STYLE) &&
         style.get_box().clone_display() == Display::None
     {
         return true;
     }
 
-    if !style.flags.intersects(ComputedValueFlags::INHERITS_CONTENT) &&
+    if !style.flags.intersects(ComputedValueFlags::CONTENT_DEPENDS_ON_INHERITED_STYLE) &&
         style.ineffective_content_property()
     {
         return true;