Auto merge of #15768 - ferjm:issue-15592-document-elementsFromPoint, r=emilio

Trigger reflow on document.elementsFromPoint

As [suggested](https://github.com/servo/servo/issues/15592#issuecomment-280379805) by @jdm `Document::nodes_from_point` now triggers a reflow.

I added a new reftest that panics with `ERROR:servo: Tried to hit test without a DisplayList` if this patch is not applied.

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #15592.
- [X] There are tests for these changes

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components/layout/lib.rs

@@ -73,7 +73,7 @@ mod linked_list;
 mod list_item;
 mod model;
 mod multicol;
-mod opaque_node;
+pub mod opaque_node;
 pub mod parallel;
 mod persistent_list;
 pub mod query;

components/layout/query.rs

@@ -94,6 +94,9 @@ pub struct LayoutThreadData {
 
     /// A list of images requests that need to be initiated.
     pub pending_images: Vec<PendingImage>,
+
+    /// A queued response for the list of nodes at a given point.
+    pub nodes_from_point_response: Vec<UntrustedNodeAddress>,
 }
 
 pub struct LayoutRPCImpl(pub Arc<Mutex<LayoutThreadData>>);
@@ -144,33 +147,10 @@ impl LayoutRPC for LayoutRPCImpl {
         }
     }
 
-    fn nodes_from_point(&self,
-                        page_point: Point2D<f32>,
-                        client_point: Point2D<f32>) -> Vec<UntrustedNodeAddress> {
-        let page_point = Point2D::new(Au::from_f32_px(page_point.x),
-                                      Au::from_f32_px(page_point.y));
-        let client_point = Point2D::new(Au::from_f32_px(client_point.x),
-                                        Au::from_f32_px(client_point.y));
-
-        let nodes_from_point_list = {
+    fn nodes_from_point_response(&self) -> Vec<UntrustedNodeAddress> {
         let &LayoutRPCImpl(ref rw_data) = self;
         let rw_data = rw_data.lock().unwrap();
-            let result = match rw_data.display_list {
-                None => panic!("Tried to hit test without a DisplayList"),
-                Some(ref display_list) => {
-                    display_list.hit_test(&page_point,
-                                          &client_point,
-                                          &rw_data.stacking_context_scroll_offsets)
-                }
-            };
-
-            result
-        };
-
-        nodes_from_point_list.iter()
-           .rev()
-           .map(|metadata| metadata.node.to_untrusted_node_address())
-           .collect()
+        rw_data.nodes_from_point_response.clone()
     }
 
     fn node_geometry(&self) -> NodeGeometryResponse {

components/layout_thread/lib.rs

@@ -63,6 +63,7 @@ use layout::flow::{self, Flow, ImmutableFlowUtils, MutableFlowUtils, MutableOwne
 use layout::flow_ref::FlowRef;
 use layout::incremental::{LayoutDamageComputation, REFLOW_ENTIRE_DOCUMENT};
 use layout::layout_debug;
+use layout::opaque_node::OpaqueNodeMethods;
 use layout::parallel;
 use layout::query::{LayoutRPCImpl, LayoutThreadData, process_content_box_request, process_content_boxes_request};
 use layout::query::{process_margin_style_query, process_node_overflow_request, process_resolved_style_request};
@@ -459,6 +460,7 @@ impl LayoutThread {
                     stacking_context_scroll_offsets: HashMap::new(),
                     text_index_response: TextIndexResponse(None),
                     pending_images: vec![],
+                    nodes_from_point_response: vec![],
                 })),
             error_reporter: CSSErrorReporter {
                 pipelineid: id,
@@ -977,6 +979,9 @@ impl LayoutThread {
                     ReflowQueryType::HitTestQuery(..) => {
                         rw_data.hit_test_response = (None, false);
                     },
+                    ReflowQueryType::NodesFromPoint(..) => {
+                        rw_data.nodes_from_point_response = Vec::new();
+                    },
                     ReflowQueryType::NodeGeometryQuery(_) => {
                         rw_data.client_rect_response = Rect::zero();
                     },
@@ -1279,6 +1284,29 @@ impl LayoutThread {
                 let node = unsafe { ServoLayoutNode::new(&node) };
                 rw_data.margin_style_response = process_margin_style_query(node);
             },
+            ReflowQueryType::NodesFromPoint(page_point, client_point) => {
+                let page_point = Point2D::new(Au::from_f32_px(page_point.x),
+                                              Au::from_f32_px(page_point.y));
+                let client_point = Point2D::new(Au::from_f32_px(client_point.x),
+                                                Au::from_f32_px(client_point.y));
+                let nodes_from_point_list = {
+                    let result = match rw_data.display_list {
+                        None => panic!("Tried to hit test without a DisplayList"),
+                        Some(ref display_list) => {
+                            display_list.hit_test(&page_point,
+                                                  &client_point,
+                                                  &rw_data.stacking_context_scroll_offsets)
+                        }
+                    };
+
+                    result
+                };
+
+                rw_data.nodes_from_point_response = nodes_from_point_list.iter()
+                   .rev()
+                   .map(|metadata| metadata.node.to_untrusted_node_address())
+                   .collect()
+            },
             ReflowQueryType::NoQuery => {}
         }
     }
@@ -1585,7 +1613,8 @@ fn get_ua_stylesheets() -> Result<UserAgentStylesheets, &'static str> {
 /// or false if it only needs stacking-relative positions.
 fn reflow_query_type_needs_display_list(query_type: &ReflowQueryType) -> bool {
     match *query_type {
-        ReflowQueryType::HitTestQuery(..) | ReflowQueryType::TextIndexQuery(..) => true,
+        ReflowQueryType::HitTestQuery(..) | ReflowQueryType::TextIndexQuery(..) |
+        ReflowQueryType::NodesFromPoint(..) => true,
         ReflowQueryType::ContentBoxQuery(_) | ReflowQueryType::ContentBoxesQuery(_) |
         ReflowQueryType::NodeGeometryQuery(_) | ReflowQueryType::NodeScrollGeometryQuery(_) |
         ReflowQueryType::NodeOverflowQuery(_) | ReflowQueryType::NodeScrollRootIdQuery(_) |

components/script/dom/document.rs

@@ -1877,7 +1877,13 @@ impl Document {
             Point2D::new(client_point.x + self.window.PageXOffset() as f32,
                          client_point.y + self.window.PageYOffset() as f32);
 
-        self.window.layout().nodes_from_point(page_point, *client_point)
+        if !self.window.reflow(ReflowGoal::ForScriptQuery,
+                               ReflowQueryType::NodesFromPoint(page_point, *client_point),
+                               ReflowReason::Query) {
+            return vec!();
+        };
+
+        self.window.layout().nodes_from_point_response()
     }
 }
 

components/script/dom/window.rs

@@ -1811,6 +1811,7 @@ fn debug_reflow_events(id: PipelineId, goal: &ReflowGoal, query_type: &ReflowQue
         ReflowQueryType::ContentBoxQuery(_n) => "\tContentBoxQuery",
         ReflowQueryType::ContentBoxesQuery(_n) => "\tContentBoxesQuery",
         ReflowQueryType::HitTestQuery(..) => "\tHitTestQuery",
+        ReflowQueryType::NodesFromPoint(..) => "\tNodesFromPoint",
         ReflowQueryType::NodeGeometryQuery(_n) => "\tNodeGeometryQuery",
         ReflowQueryType::NodeOverflowQuery(_n) => "\tNodeOverFlowQuery",
         ReflowQueryType::NodeScrollGeometryQuery(_n) => "\tNodeScrollGeometryQuery",

components/script_layout_interface/message.rs

@@ -101,6 +101,7 @@ pub enum ReflowQueryType {
     OffsetParentQuery(TrustedNodeAddress),
     MarginStyleQuery(TrustedNodeAddress),
     TextIndexQuery(TrustedNodeAddress, i32, i32),
+    NodesFromPoint(Point2D<f32>, Point2D<f32>),
 }
 
 /// Information needed for a reflow.

components/script_layout_interface/rpc.rs

@@ -40,7 +40,8 @@ pub trait LayoutRPC {
     fn margin_style(&self) -> MarginStyleResponse;
     /// Requests the list of not-yet-loaded images that were encountered in the last reflow.
     fn pending_images(&self) -> Vec<PendingImage>;
-    fn nodes_from_point(&self, page_point: Point2D<f32>, client_point: Point2D<f32>) -> Vec<UntrustedNodeAddress>;
+    /// Requests the list of nodes from the given point.
+    fn nodes_from_point_response(&self) -> Vec<UntrustedNodeAddress>;
 
     fn text_index(&self) -> TextIndexResponse;
 }

tests/wpt/mozilla/meta/MANIFEST.json

@@ -12598,6 +12598,12 @@
      {}
     ]
    ],
+   "mozilla/document_elementsFromPoint.html": [
+    [
+     "/_mozilla/mozilla/document_elementsFromPoint.html",
+     {}
+    ]
+   ],
    "mozilla/document_getElementById.html": [
     [
      "/_mozilla/mozilla/document_getElementById.html",
@@ -25137,6 +25143,10 @@
    "12eef74e9ba1a62b0302df79633cab5c48f4977f",
    "testharness"
   ],
+  "mozilla/document_elementsFromPoint.html": [
+   "00da2141b1143619351c6fbb66d677ca9002a4a8",
+   "testharness"
+  ],
   "mozilla/document_getElementById.html": [
    "ae5270afde878c8fbe9b4a89c5c3f8ff609220dc",
    "testharness"

tests/wpt/mozilla/tests/mozilla/document_elementsFromPoint.html

@@ -0,0 +1,10 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>document.elementsFromPoint does not crash due to a missing display list</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+test(function() {
+    document.elementsFromPoint(10, 10);
+}, "doesn't crash");
+</script>