Auto merge of #12757 - emilio:stylo, r=bholley,pcwalton

stylo: Stop restyling display: none elements, remove the has_changed hack that made us use ReconstructFrame unconditionally.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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r? @bholley

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components/layout/animation.rs

@@ -135,7 +135,7 @@ pub fn recalc_style_for_animations(context: &SharedLayoutContext,
                 update_style_for_animation(&context.style_context,
                                            animation,
                                            &mut fragment.style);
-                damage |= RestyleDamage::compute(Some(&old_style), &fragment.style);
+                damage |= RestyleDamage::compute(&old_style, &fragment.style);
             }
         }
     });

components/layout/construct.rs

@@ -1374,12 +1374,20 @@ impl<'a, ConcreteThreadSafeLayoutNode: ThreadSafeLayoutNode>
         // We visit the kids first and reset their HAS_NEWLY_CONSTRUCTED_FLOW flags after checking
         // them.  NOTE: Make sure not to bail out early before resetting all the flags!
         let mut need_to_reconstruct = false;
+
+        // If the node has display: none, it's possible that we haven't even
+        // styled the children once, so we need to bailout early here.
+        if node.style(self.style_context()).get_box().clone_display() == display::T::none {
+            return false;
+        }
+
         for kid in node.children() {
             if kid.flags().contains(HAS_NEWLY_CONSTRUCTED_FLOW) {
                 kid.remove_flags(HAS_NEWLY_CONSTRUCTED_FLOW);
                 need_to_reconstruct = true
             }
         }
+
         if need_to_reconstruct {
             return false
         }

components/layout/query.rs

@@ -30,6 +30,7 @@ use std::ops::Deref;
 use std::sync::{Arc, Mutex};
 use string_cache::Atom;
 use style::computed_values;
+use style::context::StyleContext;
 use style::logical_geometry::{WritingMode, BlockFlowDirection, InlineBaseDirection};
 use style::properties::longhands::{display, position};
 use style::properties::style_structs;
@@ -37,7 +38,7 @@ use style::selector_impl::PseudoElement;
 use style::selector_matching::Stylist;
 use style::values::LocalToCss;
 use style_traits::cursor::Cursor;
-use wrapper::ThreadSafeLayoutNodeHelpers;
+use wrapper::{LayoutNodeLayoutData, ThreadSafeLayoutNodeHelpers};
 
 /// Mutable data belonging to the LayoutThread.
 ///
@@ -620,11 +621,39 @@ pub fn process_node_scroll_area_request< N: LayoutNode>(requested_node: N, layou
     }
 }
 
+/// Ensures that a node's data, and all its parents' is initialized. This is
+/// needed to resolve style lazily.
+fn ensure_node_data_initialized<N: LayoutNode>(node: &N) {
+    let mut cur = Some(node.clone());
+    while let Some(current) = cur {
+        if current.borrow_data().is_some() {
+            break;
+        }
+
+        current.initialize_data();
+        cur = current.parent_node();
+    }
+}
+
 /// Return the resolved value of property for a given (pseudo)element.
 /// https://drafts.csswg.org/cssom/#resolved-value
-pub fn process_resolved_style_request<N: LayoutNode>(
-            requested_node: N, pseudo: &Option<PseudoElement>,
-            property: &Atom, layout_root: &mut FlowRef) -> Option<String> {
+pub fn process_resolved_style_request<'a, N, C>(requested_node: N,
+                                                style_context: &'a C,
+                                                pseudo: &Option<PseudoElement>,
+                                                property: &Atom,
+                                                layout_root: &mut FlowRef) -> Option<String>
+    where N: LayoutNode,
+          C: StyleContext<'a>
+{
+    use style::traversal::ensure_node_styled;
+
+    // This node might have display: none, or it's style might be not up to
+    // date, so we might need to do style recalc.
+    //
+    // FIXME(emilio): Is a bit shame we have to do this instead of in style.
+    ensure_node_data_initialized(&requested_node);
+    ensure_node_styled(requested_node, style_context);
+
     let layout_node = requested_node.to_threadsafe();
     let layout_node = match *pseudo {
         Some(PseudoElement::Before) => layout_node.get_before_pseudo(),

components/layout/traversal.rs

@@ -16,6 +16,7 @@ use std::mem;
 use style::context::SharedStyleContext;
 use style::dom::TNode;
 use style::selector_impl::ServoSelectorImpl;
+use style::traversal::RestyleResult;
 use style::traversal::{DomTraversalContext, remove_from_bloom_filter, recalc_style_at};
 use util::opts;
 use wrapper::{LayoutNodeLayoutData, ThreadSafeLayoutNodeHelpers};
@@ -69,12 +70,12 @@ impl<'lc, N> DomTraversalContext<N> for RecalcStyleAndConstructFlows<'lc>
         }
     }
 
-    fn process_preorder(&self, node: N) {
-        // FIXME(pcwalton): Stop allocating here. Ideally this should just be done by the HTML
-        // parser.
+    fn process_preorder(&self, node: N) -> RestyleResult {
+        // FIXME(pcwalton): Stop allocating here. Ideally this should just be
+        // done by the HTML parser.
         node.initialize_data();
 
-        recalc_style_at(&self.context, self.root, node);
+        recalc_style_at(&self.context, self.root, node)
     }
 
     fn process_postorder(&self, node: N) {