Auto merge of #16295 - jdm:transition-safety, r=nox

Root nodes for the duration of their CSS transitions

This ensures that we can pass a node address as part of the asynchronous
transition end notification, making it safe to fire the corresponding
DOM event on the node from the script thread. Without explicitly rooting
this node when the transition starts, we risk the node being GCed before
the transition is complete.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #14972
- [X] There are tests for these changes

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---
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1 files changed, 20 insertions, 6 deletions

diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 2f0d9dcfde3..bce898e6347 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -826,6 +826,7 @@ impl Document {
         }
     }
 
+    #[allow(unsafe_code)]
     pub fn handle_mouse_event(&self,
                               js_runtime: *mut JSRuntime,
                               button: MouseButton,
@@ -841,7 +842,9 @@ impl Document {
         let node = match self.window.hit_test_query(client_point, false) {
             Some(node_address) => {
                 debug!("node address is {:?}", node_address);
-                node::from_untrusted_node_address(js_runtime, node_address)
+                unsafe {
+                    node::from_untrusted_node_address(js_runtime, node_address)
+                }
             },
             None => return,
         };
@@ -988,13 +991,16 @@ impl Document {
         *self.last_click_info.borrow_mut() = Some((now, click_pos));
     }
 
+    #[allow(unsafe_code)]
     pub fn handle_touchpad_pressure_event(&self,
                                           js_runtime: *mut JSRuntime,
                                           client_point: Point2D<f32>,
                                           pressure: f32,
                                           phase_now: TouchpadPressurePhase) {
         let node = match self.window.hit_test_query(client_point, false) {
-            Some(node_address) => node::from_untrusted_node_address(js_runtime, node_address),
+            Some(node_address) => unsafe {
+                node::from_untrusted_node_address(js_runtime, node_address)
+            },
             None => return
         };
 
@@ -1089,6 +1095,7 @@ impl Document {
         event.fire(target);
     }
 
+    #[allow(unsafe_code)]
     pub fn handle_mouse_move_event(&self,
                                    js_runtime: *mut JSRuntime,
                                    client_point: Option<Point2D<f32>>,
@@ -1104,7 +1111,7 @@ impl Document {
         };
 
         let maybe_new_target = self.window.hit_test_query(client_point, true).and_then(|address| {
-            let node = node::from_untrusted_node_address(js_runtime, address);
+            let node = unsafe { node::from_untrusted_node_address(js_runtime, address) };
             node.inclusive_ancestors()
                 .filter_map(Root::downcast::<Element>)
                 .next()
@@ -1186,6 +1193,7 @@ impl Document {
                            ReflowReason::MouseEvent);
     }
 
+    #[allow(unsafe_code)]
     pub fn handle_touch_event(&self,
                               js_runtime: *mut JSRuntime,
                               event_type: TouchEventType,
@@ -1202,7 +1210,9 @@ impl Document {
         };
 
         let node = match self.window.hit_test_query(point, false) {
-            Some(node_address) => node::from_untrusted_node_address(js_runtime, node_address),
+            Some(node_address) => unsafe {
+                node::from_untrusted_node_address(js_runtime, node_address)
+            },
             None => return TouchEventResult::Processed(false),
         };
         let el = match node.downcast::<Element>() {
@@ -3480,7 +3490,9 @@ impl DocumentMethods for Document {
             Some(untrusted_node_address) => {
                 let js_runtime = unsafe { JS_GetRuntime(window.get_cx()) };
 
-                let node = node::from_untrusted_node_address(js_runtime, untrusted_node_address);
+                let node = unsafe {
+                    node::from_untrusted_node_address(js_runtime, untrusted_node_address)
+                };
                 let parent_node = node.GetParentNode().unwrap();
                 let element_ref = node.downcast::<Element>().unwrap_or_else(|| {
                     parent_node.downcast::<Element>().unwrap()
@@ -3515,7 +3527,9 @@ impl DocumentMethods for Document {
         // Step 1 and Step 3
         let mut elements: Vec<Root<Element>> = self.nodes_from_point(point).iter()
             .flat_map(|&untrusted_node_address| {
-                let node = node::from_untrusted_node_address(js_runtime, untrusted_node_address);
+                let node = unsafe {
+                    node::from_untrusted_node_address(js_runtime, untrusted_node_address)
+                };
                 Root::downcast::<Element>(node)
         }).collect();