implement windowproxy "delay-load-event-mode", and partially document "completely-loaded"

components/script/dom/document.rs

@@ -416,6 +416,8 @@ pub struct Document {
     /// List of tasks to execute as soon as last script/layout blocker is removed.
     #[ignore_malloc_size_of = "Measuring trait objects is hard"]
     delayed_tasks: DomRefCell<Vec<Box<dyn TaskBox>>>,
+    /// https://html.spec.whatwg.org/multipage/#completely-loaded
+    completely_loaded: Cell<bool>,
 }
 
 #[derive(JSTraceable, MallocSizeOf)]
@@ -507,6 +509,10 @@ impl Document {
         self.https_state.set(https_state);
     }
 
+    pub fn is_completely_loaded(&self) -> bool {
+        self.completely_loaded.get()
+    }
+
     pub fn is_fully_active(&self) -> bool {
         self.activity.get() == DocumentActivity::FullyActive
     }
@@ -1899,7 +1905,21 @@ impl Document {
 
     // https://html.spec.whatwg.org/multipage/#the-end
     pub fn maybe_queue_document_completion(&self) {
-        if self.loader.borrow().is_blocked() {
+        // https://html.spec.whatwg.org/multipage/#delaying-load-events-mode
+        let is_in_delaying_load_events_mode = match self.window.undiscarded_window_proxy() {
+            Some(window_proxy) => window_proxy.is_delaying_load_events_mode(),
+            None => false,
+        };
+
+        // Note: if the document is not fully active, the layout thread will have exited already,
+        // and this method will panic.
+        // The underlying problem might actually be that layout exits while it should be kept alive.
+        // See https://github.com/servo/servo/issues/22507
+        let not_ready_for_load = self.loader.borrow().is_blocked() ||
+            !self.is_fully_active() ||
+            is_in_delaying_load_events_mode;
+
+        if not_ready_for_load {
             // Step 6.
             return;
         }
@@ -1952,8 +1972,6 @@ impl Document {
 
                 window.reflow(ReflowGoal::Full, ReflowReason::DocumentLoaded);
 
-                document.notify_constellation_load();
-
                 if let Some(fragment) = document.url().fragment() {
                     document.check_and_scroll_fragment(fragment);
                 }
@@ -2008,8 +2026,26 @@ impl Document {
         // Step 11.
         // TODO: ready for post-load tasks.
 
-        // Step 12.
-        // TODO: completely loaded.
+        // Step 12: completely loaded.
+        // https://html.spec.whatwg.org/multipage/#completely-loaded
+        // TODO: fully implement "completely loaded".
+        let document = Trusted::new(self);
+        if document.root().browsing_context().is_some() {
+            self.window
+                .task_manager()
+                .dom_manipulation_task_source()
+                .queue(
+                    task!(completely_loaded: move || {
+                    let document = document.root();
+                    document.completely_loaded.set(true);
+                    // Note: this will, among others, result in the "iframe-load-event-steps" being run.
+                    // https://html.spec.whatwg.org/multipage/#iframe-load-event-steps
+                    document.notify_constellation_load();
+                }),
+                    self.window.upcast(),
+                )
+                .unwrap();
+        }
     }
 
     // https://html.spec.whatwg.org/multipage/#pending-parsing-blocking-script
@@ -2701,6 +2737,7 @@ impl Document {
             fired_unload: Cell::new(false),
             responsive_images: Default::default(),
             redirect_count: Cell::new(0),
+            completely_loaded: Cell::new(false),
             script_and_layout_blockers: Cell::new(0),
             delayed_tasks: Default::default(),
         }

components/script/dom/htmliframeelement.rs

@@ -276,8 +276,13 @@ impl HTMLIFrameElement {
         );
 
         let pipeline_id = self.pipeline_id();
-        // If the initial `about:blank` page is the current page, load with replacement enabled.
-        let replace = pipeline_id.is_some() && pipeline_id == self.about_blank_pipeline_id.get();
+        // If the initial `about:blank` page is the current page, load with replacement enabled,
+        // see https://html.spec.whatwg.org/multipage/#the-iframe-element:about:blank-3
+        let is_about_blank =
+            pipeline_id.is_some() && pipeline_id == self.about_blank_pipeline_id.get();
+        // Replacement enabled also takes into account whether the document is "completely loaded",
+        // see https://html.spec.whatwg.org/multipage/#the-iframe-element:completely-loaded
+        let replace = is_about_blank || !document.is_completely_loaded();
         self.navigate_or_reload_child_browsing_context(
             Some(load_data),
             NavigationType::Regular,

components/script/dom/window.rs

@@ -1417,7 +1417,9 @@ impl Window {
             dom_count: self.Document().dom_count(),
         };
 
-        self.layout_chan.send(Msg::Reflow(reflow)).unwrap();
+        self.layout_chan
+            .send(Msg::Reflow(reflow))
+            .expect("Layout thread disconnected.");
 
         debug!("script: layout forked");
 
@@ -1776,8 +1778,14 @@ impl Window {
             }
         }
 
-        // Step 7
+        // Step 8
         if doc.prompt_to_unload(false) {
+            if self.window_proxy().parent().is_some() {
+                // Step 10
+                // If browsingContext is a nested browsing context,
+                // then put it in the delaying load events mode.
+                self.window_proxy().start_delaying_load_events_mode();
+            }
             self.main_thread_script_chan()
                 .send(MainThreadScriptMsg::Navigate(
                     pipeline_id,

components/script/dom/windowproxy.rs

@@ -94,6 +94,9 @@ pub struct WindowProxy {
 
     /// The parent browsing context's window proxy, if this is a nested browsing context
     parent: Option<Dom<WindowProxy>>,
+
+    /// https://html.spec.whatwg.org/multipage/#delaying-load-events-mode
+    delaying_load_events_mode: Cell<bool>,
 }
 
 impl WindowProxy {
@@ -118,6 +121,7 @@ impl WindowProxy {
             disowned: Cell::new(false),
             frame_element: frame_element.map(Dom::from_ref),
             parent: parent.map(Dom::from_ref),
+            delaying_load_events_mode: Cell::new(false),
             opener,
         }
     }
@@ -314,6 +318,26 @@ impl WindowProxy {
         None
     }
 
+    /// https://html.spec.whatwg.org/multipage/#delaying-load-events-mode
+    pub fn is_delaying_load_events_mode(&self) -> bool {
+        self.delaying_load_events_mode.get()
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#delaying-load-events-mode
+    pub fn start_delaying_load_events_mode(&self) {
+        self.delaying_load_events_mode.set(true);
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#delaying-load-events-mode
+    pub fn stop_delaying_load_events_mode(&self) {
+        self.delaying_load_events_mode.set(false);
+        if let Some(document) = self.document() {
+            if !document.loader().events_inhibited() {
+                ScriptThread::mark_document_with_no_blocked_loads(&document);
+            }
+        }
+    }
+
     // https://html.spec.whatwg.org/multipage/#disowned-its-opener
     pub fn disown(&self) {
         self.disowned.set(true);