Fire live region events when a node is removed.

Adds an AXLiveRegionTracker class to keep track of live regions
in an AXTree. Uses it to fix a bug where we weren't firing the
LIVE_REGION_CHANGED event on the live root when a node was removed,
only when a node was added or changed.

I'm going to follow this up with code that optionally computes
the text of a live region change, that we can use on Android,
Chrome OS, and some older versions of macOS. So AXLiveRegionTracker
is simple now, but it will be a convenient place to put that
logic.

Bug: 560599, 930763
Change-Id: Iaff11e5adbdde533b8868226ed563567edc5589e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1464325
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727589}

ui/accessibility/BUILD.gn

@@ -62,6 +62,8 @@ jumbo_component("accessibility") {
     "ax_export.h",
     "ax_language_detection.cc",
     "ax_language_detection.h",
+    "ax_live_region_tracker.cc",
+    "ax_live_region_tracker.h",
     "ax_mode.cc",
     "ax_mode.h",
     "ax_mode_observer.h",

ui/accessibility/ax_event_generator.cc

@@ -8,6 +8,7 @@
 
 #include "base/stl_util.h"
 #include "ui/accessibility/ax_enums.mojom.h"
+#include "ui/accessibility/ax_live_region_tracker.h"
 #include "ui/accessibility/ax_node.h"
 #include "ui/accessibility/ax_role_properties.h"
 
@@ -100,8 +101,10 @@ AXEventGenerator::TargetedEvent AXEventGenerator::Iterator::operator*() const {
 AXEventGenerator::AXEventGenerator() = default;
 
 AXEventGenerator::AXEventGenerator(AXTree* tree) : tree_(tree) {
-  if (tree_)
+  if (tree_) {
     tree_->AddObserver(this);
+    live_region_tracker_ = std::make_unique<AXLiveRegionTracker>(tree_);
+  }
 }
 
 AXEventGenerator::~AXEventGenerator() {
@@ -110,11 +113,15 @@ AXEventGenerator::~AXEventGenerator() {
 }
 
 void AXEventGenerator::SetTree(AXTree* new_tree) {
-  if (tree_)
+  if (tree_) {
     tree_->RemoveObserver(this);
+    live_region_tracker_.reset();
+  }
   tree_ = new_tree;
-  if (tree_)
+  if (tree_) {
     tree_->AddObserver(this);
+    live_region_tracker_ = std::make_unique<AXLiveRegionTracker>(tree_);
+  }
 }
 
 void AXEventGenerator::ReleaseTree() {
@@ -475,6 +482,12 @@ void AXEventGenerator::OnTreeDataChanged(AXTree* tree,
 }
 
 void AXEventGenerator::OnNodeWillBeDeleted(AXTree* tree, AXNode* node) {
+  if (node->data().HasStringAttribute(
+          ax::mojom::StringAttribute::kContainerLiveStatus)) {
+    FireLiveRegionEvents(node);
+    live_region_tracker_->OnNodeWillBeDeleted(node);
+  }
+
   DCHECK_EQ(tree_, tree);
   tree_events_.erase(node);
 }
@@ -506,6 +519,14 @@ void AXEventGenerator::OnAtomicUpdateFinished(
   }
 
   for (const auto& change : changes) {
+    if ((change.type == NODE_CREATED || change.type == SUBTREE_CREATED ||
+         change.type == NODE_REPARENTED || change.type == SUBTREE_REPARENTED)) {
+      if (change.node->data().HasStringAttribute(
+              ax::mojom::StringAttribute::kContainerLiveStatus)) {
+        live_region_tracker_->TrackNode(change.node);
+      }
+    }
+
     if (change.type == SUBTREE_CREATED) {
       AddEvent(change.node, Event::SUBTREE_CREATED);
     } else if (change.type != NODE_CREATED) {
@@ -525,23 +546,29 @@ void AXEventGenerator::OnAtomicUpdateFinished(
 }
 
 void AXEventGenerator::FireLiveRegionEvents(AXNode* node) {
-  AXNode* live_root = node;
-  while (live_root && !live_root->data().HasStringAttribute(
-                          ax::mojom::StringAttribute::kLiveStatus))
-    live_root = live_root->parent();
-
-  if (live_root &&
-      !live_root->data().GetBoolAttribute(ax::mojom::BoolAttribute::kBusy) &&
-      live_root->data().GetStringAttribute(
-          ax::mojom::StringAttribute::kLiveStatus) != "off") {
-    // Fire LIVE_REGION_NODE_CHANGED on each node that changed.
-    if (!node->data()
-             .GetStringAttribute(ax::mojom::StringAttribute::kName)
-             .empty())
-      AddEvent(node, Event::LIVE_REGION_NODE_CHANGED);
-    // Fire LIVE_REGION_CHANGED on the root of the live region.
-    AddEvent(live_root, Event::LIVE_REGION_CHANGED);
+  AXNode* live_root = live_region_tracker_->GetLiveRoot(node);
+
+  // Note that |live_root| might be nullptr if a live region was just added.
+  if (!live_root)
+    return;
+
+  if (live_root->data().GetBoolAttribute(ax::mojom::BoolAttribute::kBusy))
+    return;
+
+  std::string live_status = live_root->data().GetStringAttribute(
+      ax::mojom::StringAttribute::kLiveStatus);
+  if (live_status != "polite" && live_status != "assertive")
+    return;
+
+  // Fire LIVE_REGION_NODE_CHANGED on each node that changed.
+  if (!node->data()
+           .GetStringAttribute(ax::mojom::StringAttribute::kName)
+           .empty()) {
+    AddEvent(node, Event::LIVE_REGION_NODE_CHANGED);
   }
+
+  // Fire LIVE_REGION_CHANGED on the root of the live region.
+  AddEvent(live_root, Event::LIVE_REGION_CHANGED);
 }
 
 void AXEventGenerator::FireActiveDescendantEvents() {

ui/accessibility/ax_event_generator.h

@@ -6,8 +6,10 @@
 #define UI_ACCESSIBILITY_AX_EVENT_GENERATOR_H_
 
 #include <map>
+#include <memory>
 #include <ostream>
 #include <set>
+#include <string>
 #include <vector>
 
 #include "ui/accessibility/ax_export.h"
@@ -16,6 +18,8 @@
 
 namespace ui {
 
+class AXLiveRegionTracker;
+
 // Subclass of AXTreeObserver that automatically generates AXEvents to fire
 // based on changes to an accessibility tree.  Every platform
 // tends to want different events, so this class lets each platform
@@ -232,6 +236,9 @@ class AX_EXPORT AXEventGenerator : public AXTreeObserver {
   // Valid between the call to OnIntAttributeChanged and the call to
   // OnAtomicUpdateFinished. List of nodes whose active descendant changed.
   std::vector<AXNode*> active_descendant_changed_;
+
+  // Helper that tracks live regions.
+  std::unique_ptr<AXLiveRegionTracker> live_region_tracker_;
 };
 
 AX_EXPORT std::ostream& operator<<(std::ostream& os,

ui/accessibility/ax_event_generator_unittest.cc

@@ -1370,4 +1370,41 @@ TEST(AXEventGeneratorTest, MultilineStateChanged) {
           HasEventAtNode(AXEventGenerator::Event::STATE_CHANGED, 1)));
 }
 
+TEST(AXEventGeneratorTest, LiveRegionNodeRemoved) {
+  AXTreeUpdate initial_state;
+  initial_state.root_id = 1;
+  initial_state.nodes.resize(3);
+  initial_state.nodes[0].id = 1;
+  initial_state.nodes[0].AddStringAttribute(
+      ax::mojom::StringAttribute::kLiveStatus, "polite");
+  initial_state.nodes[0].AddStringAttribute(
+      ax::mojom::StringAttribute::kContainerLiveStatus, "polite");
+  initial_state.nodes[0].child_ids = {2, 3};
+  initial_state.nodes[1].id = 2;
+  initial_state.nodes[1].role = ax::mojom::Role::kStaticText;
+  initial_state.nodes[1].AddStringAttribute(
+      ax::mojom::StringAttribute::kContainerLiveStatus, "polite");
+  initial_state.nodes[1].AddStringAttribute(ax::mojom::StringAttribute::kName,
+                                            "Before 1");
+  initial_state.nodes[2].id = 3;
+  initial_state.nodes[2].role = ax::mojom::Role::kStaticText;
+  initial_state.nodes[2].AddStringAttribute(
+      ax::mojom::StringAttribute::kContainerLiveStatus, "polite");
+  initial_state.nodes[2].AddStringAttribute(ax::mojom::StringAttribute::kName,
+                                            "Before 2");
+  AXTree tree(initial_state);
+
+  AXEventGenerator event_generator(&tree);
+  AXTreeUpdate update = initial_state;
+  update.nodes.resize(1);
+  update.nodes[0].child_ids = {2};
+
+  EXPECT_TRUE(tree.Unserialize(update));
+  EXPECT_THAT(
+      event_generator,
+      UnorderedElementsAre(
+          HasEventAtNode(AXEventGenerator::Event::CHILDREN_CHANGED, 1),
+          HasEventAtNode(AXEventGenerator::Event::LIVE_REGION_CHANGED, 1)));
+}
+
 }  // namespace ui

ui/accessibility/ax_live_region_tracker.cc

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ui/accessibility/ax_live_region_tracker.h"
+
+#include "base/stl_util.h"
+#include "ui/accessibility/ax_node.h"
+#include "ui/accessibility/ax_role_properties.h"
+
+namespace ui {
+
+AXLiveRegionTracker::AXLiveRegionTracker(AXTree* tree) : tree_(tree) {
+  InitializeLiveRegionNodeToRoot(tree_->root(), nullptr);
+}
+
+AXLiveRegionTracker::~AXLiveRegionTracker() {}
+
+void AXLiveRegionTracker::TrackNode(AXNode* node) {
+  LOG(ERROR) << "TrackNode " << node->data().ToString();
+  AXNode* live_root = node;
+  while (live_root && !live_root->HasStringAttribute(
+                          ax::mojom::StringAttribute::kLiveStatus))
+    live_root = live_root->parent();
+  if (live_root) {
+    LOG(ERROR) << "  Live root: " << live_root->data().ToString();
+    live_region_node_to_root_[node] = live_root;
+  } else
+    LOG(ERROR) << "  No live root";
+}
+
+void AXLiveRegionTracker::OnNodeWillBeDeleted(AXNode* node) {
+  LOG(ERROR) << "OnNodeWillBeDeleted " << node->data().ToString();
+  live_region_node_to_root_.erase(node);
+}
+
+AXNode* AXLiveRegionTracker::GetLiveRoot(AXNode* node) {
+  LOG(ERROR) << "GetLiveRoot for " << node->data().ToString();
+  auto iter = live_region_node_to_root_.find(node);
+  if (iter != live_region_node_to_root_.end())
+    return iter->second;
+  return nullptr;
+}
+
+void AXLiveRegionTracker::InitializeLiveRegionNodeToRoot(AXNode* node,
+                                                         AXNode* current_root) {
+  if (!current_root &&
+      node->HasStringAttribute(ax::mojom::StringAttribute::kLiveStatus)) {
+    current_root = node;
+  }
+
+  if (current_root)
+    live_region_node_to_root_[node] = current_root;
+
+  for (size_t i = 0; i < node->children().size(); i++)
+    InitializeLiveRegionNodeToRoot(node->children()[i], current_root);
+}
+
+}  // namespace ui

ui/accessibility/ax_live_region_tracker.h

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_ACCESSIBILITY_AX_LIVE_REGION_TRACKER_H_
+#define UI_ACCESSIBILITY_AX_LIVE_REGION_TRACKER_H_
+
+#include <map>
+#include <set>
+#include <vector>
+
+#include "ui/accessibility/ax_tree.h"
+
+namespace ui {
+
+// Class that works with AXEventGenerator to track live regions in
+// an AXTree.
+class AXLiveRegionTracker {
+ public:
+  explicit AXLiveRegionTracker(AXTree* tree);
+
+  ~AXLiveRegionTracker();
+
+  void TrackNode(AXNode* node);
+  void OnNodeWillBeDeleted(AXNode* node);
+  AXNode* GetLiveRoot(AXNode* node);
+
+ private:
+  void InitializeLiveRegionNodeToRoot(AXNode* node, AXNode* current_root);
+
+  AXTree* tree_;  // Not owned.
+
+  // Map from live region node to its live region root.
+  std::map<AXNode*, AXNode*> live_region_node_to_root_;
+
+  DISALLOW_COPY_AND_ASSIGN(AXLiveRegionTracker);
+};
+
+}  // namespace ui
+
+#endif  // UI_ACCESSIBILITY_AX_LIVE_REGION_TRACKER_H_