Auto merge of #19881 - jonleighton:issue-19811, r=emilio

Add layout RPC query for getting an element's style

This enables us to implement Element::has_css_layout_box() in a more
direct way, and also enables us to remove some of the existing more
specific queries.

Fixes #19811.

r? @emilio

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1 files changed, 30 insertions, 32 deletions

diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index c6224e7dc87..a1bcaa0437e 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -348,27 +348,24 @@ impl Element {
     }
 
     // https://drafts.csswg.org/cssom-view/#css-layout-box
-    //
-    // We'll have no content box if there's no fragment for the node, and we use
-    // bounding_content_box, for simplicity, to detect this (rather than making a more specific
-    // query to the layout thread).
     fn has_css_layout_box(&self) -> bool {
-        self.upcast::<Node>().bounding_content_box().is_some()
+        let style = self.upcast::<Node>().style();
+
+        // style will be None for elements in a display: none subtree. otherwise, the element has a
+        // layout box iff it doesn't have display: none.
+        style.map_or(false, |s| !s.get_box().clone_display().is_none())
     }
 
     // https://drafts.csswg.org/cssom-view/#potentially-scrollable
     fn potentially_scrollable(&self) -> bool {
-        self.has_css_layout_box() &&
-        !self.overflow_x_is_visible() &&
-        !self.overflow_y_is_visible()
+        self.has_css_layout_box() && !self.has_any_visible_overflow()
     }
 
     // https://drafts.csswg.org/cssom-view/#scrolling-box
     fn has_scrolling_box(&self) -> bool {
         // TODO: scrolling mechanism, such as scrollbar (We don't have scrollbar yet)
         //       self.has_scrolling_mechanism()
-        self.overflow_x_is_hidden() ||
-        self.overflow_y_is_hidden()
+        self.has_any_hidden_overflow()
     }
 
     fn has_overflow(&self) -> bool {
@@ -376,32 +373,33 @@ impl Element {
         self.ScrollWidth() > self.ClientWidth()
     }
 
-    // used value of overflow-x is "visible"
-    fn overflow_x_is_visible(&self) -> bool {
-        let window = window_from_node(self);
-        let overflow_pair = window.overflow_query(self.upcast::<Node>().to_trusted_node_address());
-        overflow_pair.x == overflow_x::computed_value::T::Visible
-    }
+    // TODO: Once #19183 is closed (overflow-x/y types moved out of mako), then we could implement
+    //       a more generic `fn has_some_overflow(&self, overflow: Overflow)` rather than have
+    //       these two `has_any_{visible,hidden}_overflow` methods which are very structurally
+    //       similar.
 
-    // used value of overflow-y is "visible"
-    fn overflow_y_is_visible(&self) -> bool {
-        let window = window_from_node(self);
-        let overflow_pair = window.overflow_query(self.upcast::<Node>().to_trusted_node_address());
-        overflow_pair.y == overflow_y::computed_value::T::Visible
-    }
+    /// Computed value of overflow-x or overflow-y is "visible"
+    fn has_any_visible_overflow(&self) -> bool {
+        let style = self.upcast::<Node>().style();
 
-    // used value of overflow-x is "hidden"
-    fn overflow_x_is_hidden(&self) -> bool {
-        let window = window_from_node(self);
-        let overflow_pair = window.overflow_query(self.upcast::<Node>().to_trusted_node_address());
-        overflow_pair.x == overflow_x::computed_value::T::Hidden
+        style.map_or(false, |s| {
+            let box_ = s.get_box();
+
+            box_.clone_overflow_x() == overflow_x::computed_value::T::Visible ||
+                box_.clone_overflow_y() == overflow_y::computed_value::T::Visible
+        })
     }
 
-    // used value of overflow-y is "hidden"
-    fn overflow_y_is_hidden(&self) -> bool {
-        let window = window_from_node(self);
-        let overflow_pair = window.overflow_query(self.upcast::<Node>().to_trusted_node_address());
-        overflow_pair.y == overflow_y::computed_value::T::Hidden
+    /// Computed value of overflow-x or overflow-y is "hidden"
+    fn has_any_hidden_overflow(&self) -> bool {
+        let style = self.upcast::<Node>().style();
+
+        style.map_or(false, |s| {
+            let box_ = s.get_box();
+
+            box_.clone_overflow_x() == overflow_x::computed_value::T::Hidden ||
+                box_.clone_overflow_y() == overflow_y::computed_value::T::Hidden
+        })
     }
 }