Prevent crash after moving the last item from a folder

Existing logic of unfoldering the last item to the right:
1) calculate target position as "folder index + 1";
2) move item at that position;
3) delete the folder;
4) reparented item moves one position back.

The issue was that code continues using position from 1) after 4).
This leads to:
1) focusing the wrong (+ 1) item, if the folder was not at the end;
2) crash, if the folder was at the end of the grid.

(cherry picked from commit efe4528)

Bug: b/262715563
Change-Id: I3208635b8b612057440fc5be993bd8abb5e40b1b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4117547
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Commit-Queue: Artsiom Mitrokhin <amitrokhin@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1086060}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4135539
Cr-Commit-Position: refs/branch-heads/5481@{#120}
Cr-Branched-From: 130f3e4-refs/heads/main@{#1084008}

ash/app_list/views/apps_grid_view.cc

@@ -2045,21 +2045,34 @@ void AppsGridView::HandleKeyboardReparent(
   DCHECK(!folder_delegate_);
   DCHECK(view_model_.GetIndexOfView(original_parent_item_view).has_value());
 
+  const std::string reparented_item_id = reparented_view->item()->id();
+
   // Set |original_parent_item_view| selected so |target_index| will be
   // computed relative to the open folder.
   SetSelectedView(original_parent_item_view);
   const GridIndex target_index = GetTargetGridIndexForKeyboardReparent(
       GetIndexOfView(original_parent_item_view), key_code);
   ReparentItemForReorder(reparented_view->item(), target_index);
 
+  // `target_index` could point to an invalid/wrong position after reparenting.
+  // This happens after trying to move the last item from the folder
+  // to the right (`target_index` is "folder index + 1", but after reparenting
+  // it actually moves one position back).
+  const AppListItem* const item_after_reparent =
+      item_list_->FindItem(reparented_item_id);
+  DCHECK(item_after_reparent);
+  const int final_model_index = GetModelIndexOfItem(item_after_reparent);
+  const GridIndex final_grid_index =
+      GetGridIndexFromIndexInViewModel(final_model_index);
+
   // Update paging because the move could have resulted in a
   // page getting created.
   UpdatePaging();
 
   Layout();
-  EnsureViewVisible(target_index);
-  GetViewAtIndex(target_index)->RequestFocus();
-  AnnounceReorder(target_index);
+  EnsureViewVisible(final_grid_index);
+  GetViewAtIndex(final_grid_index)->RequestFocus();
+  AnnounceReorder(final_grid_index);
 
   RecordAppMovingTypeMetrics(kMoveByKeyboardOutOfFolder);
 }

ash/app_list/views/apps_grid_view_unittest.cc

@@ -3250,6 +3250,39 @@ TEST_P(AppsGridViewClamshellAndTabletTest,
   EXPECT_TRUE(apps_grid_view_->IsSelectedView(new_folder));
 }
 
+TEST_P(AppsGridViewClamshellAndTabletTest,
+       MoveLastItemFromFolderToRightDoesNotCrash) {
+  ui::test::EventGenerator* const event_generator = GetEventGenerator();
+
+  // Create a folder with two items in it.
+  model_->CreateAndPopulateFolderWithApps(2);
+  AppListItemView* folder_view = test_api_->GetViewAtIndex(GridIndex(0, 0));
+
+  // Open the folder.
+  folder_view->RequestFocus();
+  event_generator->PressAndReleaseKey(ui::VKEY_RETURN);
+  EXPECT_TRUE(GetAppListTestHelper()->IsInFolderView());
+
+  // An item inside the folder should be in focus. Move it to the left to put it
+  // before the folder icon.
+  event_generator->PressAndReleaseKey(ui::VKEY_LEFT,
+                                      ui::EF_CONTROL_DOWN | ui::EF_SHIFT_DOWN);
+  EXPECT_FALSE(GetAppListTestHelper()->IsInFolderView());
+  EXPECT_TRUE(test_api_->GetViewAtIndex(GridIndex(0, 0))->HasFocus());
+
+  // Open the folder again.
+  folder_view->RequestFocus();
+  event_generator->PressAndReleaseKey(ui::VKEY_RETURN);
+  EXPECT_TRUE(GetAppListTestHelper()->IsInFolderView());
+
+  // An item inside the folder should be in focus. Move it to the right to put
+  // it after/instead the folder icon. No crash happens.
+  event_generator->PressAndReleaseKey(ui::VKEY_RIGHT,
+                                      ui::EF_CONTROL_DOWN | ui::EF_SHIFT_DOWN);
+  EXPECT_FALSE(GetAppListTestHelper()->IsInFolderView());
+  EXPECT_TRUE(test_api_->GetViewAtIndex(GridIndex(0, 1))->HasFocus());
+}
+
 TEST_P(AppsGridViewTabletTest, TouchDragFlipToNextPage) {
   ASSERT_TRUE(paged_apps_grid_view_);