Auto merge of #20865 - gterzian:improve_spec_compliance_window_close, r=cbrewster

improve spec compliance of window.close

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Improve the spec compliance of https://html.spec.whatwg.org/multipage/window-object.html#dom-window-close, mainly by implementing the steps related to [closing a browsing context](https://html.spec.whatwg.org/multipage/window-object.html#close-a-browsing-context)

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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/script/dom/window.rs

@@ -11,6 +11,7 @@ use devtools_traits::{ScriptToDevtoolsControlMsg, TimelineMarker, TimelineMarker
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::DocumentBinding::{DocumentMethods, DocumentReadyState};
 use dom::bindings::codegen::Bindings::FunctionBinding::Function;
+use dom::bindings::codegen::Bindings::HistoryBinding::HistoryBinding::HistoryMethods;
 use dom::bindings::codegen::Bindings::PermissionStatusBinding::PermissionState;
 use dom::bindings::codegen::Bindings::RequestBinding::RequestInit;
 use dom::bindings::codegen::Bindings::WindowBinding::{self, FrameRequestCallback, WindowMethods};
@@ -543,9 +544,27 @@ impl WindowMethods for Window {
 
     // https://html.spec.whatwg.org/multipage/#dom-window-close
     fn Close(&self) {
-        self.main_thread_script_chan()
-            .send(MainThreadScriptMsg::ExitWindow(self.upcast::<GlobalScope>().pipeline_id()))
-            .unwrap();
+        // Note: check the length of the "session history", as opposed to the joint session history?
+        // see https://github.com/whatwg/html/issues/3734
+        if let Ok(history_length) = self.History().GetLength() {
+            // TODO: allow auxilliary browsing contexts created by script to be script-closeable,
+            // regardless of history length.
+            // https://html.spec.whatwg.org/multipage/#script-closable
+            let is_script_closable = self.is_top_level() && history_length == 1;
+            if is_script_closable {
+                let doc = self.Document();
+                // https://html.spec.whatwg.org/multipage/#closing-browsing-contexts
+                // Step 1, prompt to unload.
+                if doc.prompt_to_unload(false) {
+                    // Step 2, unload.
+                    doc.unload(false, false);
+                    // Step 3, remove from the user interface
+                    let _ = self.send_to_embedder(EmbedderMsg::CloseBrowser);
+                    // Step 4, discard browsing context.
+                    let _ = self.send_to_constellation(ScriptMsg::DiscardTopLevelBrowsingContext);
+                }
+            }
+        }
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-document-2

components/script/script_thread.rs

@@ -220,9 +220,6 @@ enum MixedMessage {
 pub enum MainThreadScriptMsg {
     /// Common variants associated with the script messages
     Common(CommonScriptMsg),
-    /// Notifies the script that a window associated with a particular pipeline
-    /// should be closed (only dispatched to ScriptThread).
-    ExitWindow(PipelineId),
     /// Begins a content-initiated load on the specified pipeline (only
     /// dispatched to ScriptThread). Allows for a replace bool to be passed. If true,
     /// the current entry will be replaced instead of a new entry being added.
@@ -1193,7 +1190,6 @@ impl ScriptThread {
                     MainThreadScriptMsg::Common(CommonScriptMsg::Task(_, _, pipeline_id)) =>
                         pipeline_id,
                     MainThreadScriptMsg::Common(CommonScriptMsg::CollectReports(_)) => None,
-                    MainThreadScriptMsg::ExitWindow(pipeline_id) => Some(pipeline_id),
                     MainThreadScriptMsg::Navigate(pipeline_id, ..) => Some(pipeline_id),
                     MainThreadScriptMsg::WorkletLoaded(pipeline_id) => Some(pipeline_id),
                     MainThreadScriptMsg::RegisterPaintWorklet { pipeline_id, .. } => Some(pipeline_id),
@@ -1344,9 +1340,6 @@ impl ScriptThread {
             MainThreadScriptMsg::Navigate(parent_pipeline_id, load_data, replace) => {
                 self.handle_navigate(parent_pipeline_id, None, load_data, replace)
             },
-            MainThreadScriptMsg::ExitWindow(id) => {
-                self.handle_exit_window_msg(id)
-            },
             MainThreadScriptMsg::Common(CommonScriptMsg::Task(_, task, _)) => {
                 task.run_box()
             }
@@ -1715,20 +1708,6 @@ impl ScriptThread {
         window.set_window_size(new_size);
     }
 
-    /// We have gotten a window.close from script, which we pass on to the compositor.
-    /// We do not shut down the script thread now, because the compositor will ask the
-    /// constellation to shut down the pipeline, which will clean everything up
-    /// normally. If we do exit, we will tear down the DOM nodes, possibly at a point
-    /// where layout is still accessing them.
-    fn handle_exit_window_msg(&self, id: PipelineId) {
-        debug!("script thread handling exit window msg");
-
-        // TODO(tkuehn): currently there is only one window,
-        // so this can afford to be naive and just shut down the
-        // constellation. In the future it'll need to be smarter.
-        self.script_sender.send((id, ScriptMsg::Exit)).unwrap();
-    }
-
     /// We have received notification that the response associated with a load has completed.
     /// Kick off the document and frame tree creation process using the result.
     fn handle_page_headers_available(&self, id: &PipelineId,