LibWeb+WebContent+Browser: Plumb visibility state from GUI to web pages

OOPWV now reacts to show/hide events and informs LibWeb about the state
change. This makes visibilitychange events fire when switching tabs. :^)

Userland/Libraries/LibWeb/HTML/BrowsingContext.cpp

@@ -1113,7 +1113,7 @@ DOM::ExceptionOr<void> BrowsingContext::traverse_the_history(size_t entry_index,
             new_document->set_page_showing(true);
 
             // 3. Update the visibility state of newDocument to "hidden".
-            new_document->update_the_visibility_state("hidden");
+            new_document->update_the_visibility_state(VisibilityState::Hidden);
 
             // 4. Fire a page transition event named pageshow at newDocument's relevant global object with true.
             auto& window = verify_cast<HTML::Window>(relevant_global_object(*new_document));
@@ -1248,18 +1248,55 @@ BrowsingContext const* BrowsingContext::the_one_permitted_sandboxed_navigator()
 }
 
 // https://html.spec.whatwg.org/multipage/browsers.html#document-family
-bool BrowsingContext::document_family_contains(DOM::Document const& document) const
+Vector<JS::Handle<DOM::Document>> BrowsingContext::document_family() const
 {
-    HashTable<DOM::Document const*> family;
-
+    HashTable<DOM::Document*> documents;
     for (auto& entry : m_session_history) {
         if (!entry.document)
             continue;
-        if (family.set(entry.document) == AK::HashSetResult::ReplacedExistingEntry)
+        if (documents.set(entry.document.ptr()) == AK::HashSetResult::ReplacedExistingEntry)
             continue;
-        // FIXME: The document family of a Document object consists of the union of all the document families of the browsing contexts in the list of the descendant browsing contexts of the Document object.
+        for (auto& context : entry.document->list_of_descendant_browsing_contexts()) {
+            for (auto& document : context->document_family()) {
+                documents.set(document.ptr());
+            }
+        }
     }
 
-    return family.contains(&document);
+    Vector<JS::Handle<DOM::Document>> family;
+    for (auto* document : documents) {
+        family.append(*document);
+    }
+    return family;
 }
+
+// https://html.spec.whatwg.org/multipage/browsers.html#document-family
+bool BrowsingContext::document_family_contains(DOM::Document const& document) const
+{
+    return document_family().first_matching([&](auto& entry) { return entry.ptr() == &document; }).has_value();
+}
+
+VisibilityState BrowsingContext::system_visibility_state() const
+{
+    return m_system_visibility_state;
+}
+
+// https://html.spec.whatwg.org/multipage/interaction.html#system-visibility-state
+void BrowsingContext::set_system_visibility_state(VisibilityState visibility_state)
+{
+    if (m_system_visibility_state == visibility_state)
+        return;
+    m_system_visibility_state = visibility_state;
+
+    // When a user-agent determines that the system visibility state for top-level browsing context context
+    // has changed to newState, it must queue a task on the user interaction task source to update
+    // the visibility state of all the Document objects in the top-level browsing context's document family with newState.
+    auto document_family = top_level_browsing_context().document_family();
+    queue_global_task(Task::Source::UserInteraction, Bindings::main_thread_vm().current_realm()->global_object(), [visibility_state, document_family = move(document_family)]() mutable {
+        for (auto& document : document_family) {
+            document->update_the_visibility_state(visibility_state);
+        }
+    });
+}
+
 }

Userland/Libraries/LibWeb/HTML/BrowsingContext.h

@@ -18,6 +18,7 @@
 #include <LibWeb/HTML/HistoryHandlingBehavior.h>
 #include <LibWeb/HTML/Origin.h>
 #include <LibWeb/HTML/SessionHistoryEntry.h>
+#include <LibWeb/HTML/VisibilityState.h>
 #include <LibWeb/Loader/FrameLoader.h>
 #include <LibWeb/Page/EventHandler.h>
 #include <LibWeb/Platform/Timer.h>
@@ -158,8 +159,12 @@ public:
     // https://html.spec.whatwg.org/multipage/browsing-the-web.html#traverse-the-history
     DOM::ExceptionOr<void> traverse_the_history(size_t entry_index, HistoryHandlingBehavior = HistoryHandlingBehavior::Default, bool explicit_history_navigation = false);
 
+    Vector<JS::Handle<DOM::Document>> document_family() const;
     bool document_family_contains(DOM::Document const&) const;
 
+    VisibilityState system_visibility_state() const;
+    void set_system_visibility_state(VisibilityState);
+
 private:
     explicit BrowsingContext(Page&, HTML::BrowsingContextContainer*);
 
@@ -205,6 +210,9 @@ private:
 
     // https://html.spec.whatwg.org/multipage/browsers.html#tlbc-group
     RefPtr<BrowsingContextGroup> m_group;
+
+    // https://html.spec.whatwg.org/multipage/interaction.html#system-visibility-state
+    VisibilityState m_system_visibility_state { VisibilityState::Hidden };
 };
 
 HTML::Origin determine_the_origin(BrowsingContext const& browsing_context, Optional<AK::URL> url, SandboxingFlagSet sandbox_flags, Optional<HTML::Origin> invocation_origin);

Userland/Libraries/LibWeb/HTML/BrowsingContextContainer.cpp

@@ -18,6 +18,12 @@
 
 namespace Web::HTML {
 
+HashTable<BrowsingContextContainer*>& BrowsingContextContainer::all_instances()
+{
+    static HashTable<BrowsingContextContainer*> set;
+    return set;
+}
+
 BrowsingContextContainer::BrowsingContextContainer(DOM::Document& document, DOM::QualifiedName qualified_name)
     : HTMLElement(document, move(qualified_name))
 {

Userland/Libraries/LibWeb/HTML/BrowsingContextContainer.h

@@ -16,6 +16,8 @@ class BrowsingContextContainer : public HTMLElement {
 public:
     virtual ~BrowsingContextContainer() override;
 
+    static HashTable<BrowsingContextContainer*>& all_instances();
+
     BrowsingContext* nested_browsing_context() { return m_nested_browsing_context; }
     BrowsingContext const* nested_browsing_context() const { return m_nested_browsing_context; }
 

Userland/Libraries/LibWeb/HTML/VisibilityState.h

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Web::HTML {
+
+enum VisibilityState {
+    Hidden,
+    Visible,
+};
+
+}