Always trigger an input sources change event on session creation

components/script/dom/xr.rs

@@ -284,7 +284,6 @@ impl XR {
                 return;
             },
         };
-
         let session = XRSession::new(&self.global(), session, mode, frame_receiver);
         if mode == XRSessionMode::Inline {
             self.active_inline_sessions
@@ -294,6 +293,9 @@ impl XR {
             self.set_active_immersive_session(&session);
         }
         promise.resolve_native(&session);
+        // https://github.com/immersive-web/webxr/issues/961
+        // This must be called _after_ the promise is resolved
+        session.setup_initial_inputs();
     }
 
     pub fn get_displays(&self) -> Result<Vec<DomRoot<VRDisplay>>, ()> {

components/script/dom/xrinputsourcearray.rs

@@ -38,30 +38,22 @@ impl XRInputSourceArray {
         )
     }
 
-    pub fn set_initial_inputs(&self, session: &XRSession) {
+    pub fn add_input_sources(&self, session: &XRSession, inputs: &[InputSource]) {
         let mut input_sources = self.input_sources.borrow_mut();
         let global = self.global();
-        session.with_session(|sess| {
-            for info in sess.initial_inputs() {
-                // XXXManishearth we should be able to listen for updates
-                // to the input sources
-                let input = XRInputSource::new(&global, &session, info.clone());
-                input_sources.push(Dom::from_ref(&input));
-            }
-        });
-    }
 
-    pub fn add_input_source(&self, session: &XRSession, info: InputSource) {
+        let mut added = vec![];
-        let mut input_sources = self.input_sources.borrow_mut();
+        for info in inputs {
-        let global = self.global();
+            // This is quadratic, but won't be a problem for the only case
+            // where we add multiple input sources (the initial input sources case)
             debug_assert!(
                 input_sources.iter().find(|i| i.id() == info.id).is_none(),
                 "Should never add a duplicate input id!"
             );
-        let input = XRInputSource::new(&global, &session, info);
+            let input = XRInputSource::new(&global, &session, info.clone());
             input_sources.push(Dom::from_ref(&input));
-
+            added.push(input);
-        let added = [input];
+        }
 
         let event = XRInputSourcesChangeEvent::new(
             &global,

components/script/dom/xrsession.rs

@@ -136,7 +136,6 @@ impl XRSession {
             global,
             XRSessionBinding::Wrap,
         );
-        input_sources.set_initial_inputs(&ret);
         ret.attach_event_handler();
         ret.setup_raf_loop(frame_receiver);
         ret
@@ -208,6 +207,36 @@ impl XRSession {
         self.session.borrow_mut().set_event_dest(sender);
     }
 
+    // Must be called after the promise for session creation is resolved
+    // https://github.com/immersive-web/webxr/issues/961
+    //
+    // This enables content that assumes all input sources are accompanied
+    // by an inputsourceschange event to work properly. Without
+    pub fn setup_initial_inputs(&self) {
+        let initial_inputs = self.session.borrow().initial_inputs().to_owned();
+
+        if initial_inputs.is_empty() {
+            // do not fire an empty event
+            return;
+        }
+
+        let global = self.global();
+        let window = global.as_window();
+        let (task_source, canceller) = window
+            .task_manager()
+            .dom_manipulation_task_source_with_canceller();
+        let this = Trusted::new(self);
+        // Queue a task so that it runs after resolve()'s microtasks complete
+        // so that content has a chance to attach a listener for inputsourceschange
+        let _ = task_source.queue_with_canceller(
+            task!(session_initial_inputs: move || {
+                let this = this.root();
+                this.input_sources.add_input_sources(&this, &initial_inputs);
+            }),
+            &canceller,
+        );
+    }
+
     fn event_callback(&self, event: XREvent) {
         match event {
             XREvent::SessionEnd => {
@@ -290,7 +319,7 @@ impl XRSession {
                 event.upcast::<Event>().fire(self.upcast());
             },
             XREvent::AddInput(info) => {
-                self.input_sources.add_input_source(self, info);
+                self.input_sources.add_input_sources(self, &[info]);
             },
             XREvent::RemoveInput(id) => {
                 self.input_sources.remove_input_source(self, id);