Enable avoid_void_async lint

app/analysis_options.yaml

@@ -3,6 +3,7 @@ include: package:flutter_lints/flutter.yaml
 linter:
   rules:
     unawaited_futures: true
+    avoid_void_async: true
     depend_on_referenced_packages: false
     prefer_interpolation_to_compose_strings: false
     no_leading_underscores_for_local_identifiers: false

app/lib/metadata_task_manager.dart

@@ -99,7 +99,7 @@ class MetadataTaskManager {
     }
   }
 
-  void _handleStream() async {
+  Future<void> _handleStream() async {
     await for (final task in _streamController.stream) {
       if (Pref().isEnableExifOr()) {
         _log.info("[_doTask] Executing task: $task");

app/lib/service.dart

@@ -54,7 +54,7 @@ void stopService() {
 }
 
 @visibleForTesting
-void serviceMain() async {
+Future<void> serviceMain() async {
   _Service._shouldRun.value = true;
   WidgetsFlutterBinding.ensureInitialized();
 

app/lib/widget/album_browser.dart

@@ -362,7 +362,7 @@ class _AlbumBrowserState extends State<AlbumBrowser>
             album: _album));
   }
 
-  void _onSharePressed(BuildContext context) async {
+  Future<void> _onSharePressed(BuildContext context) async {
     await _showSharedAlbumInfoDialog();
     await showDialog(
       context: context,

app/lib/widget/album_browser_mixin.dart

@@ -220,7 +220,7 @@ mixin AlbumBrowserMixin<T extends StatefulWidget>
     }
   }
 
-  void _onAddToCollectionPressed(
+  Future<void> _onAddToCollectionPressed(
       BuildContext context, Account account, Album album) async {
     Album? newAlbum;
     try {

app/lib/widget/album_importer.dart

@@ -216,7 +216,7 @@ class _AlbumImporterState extends State<AlbumImporter> {
     }
   }
 
-  void _onImportPressed(BuildContext context) async {
+  Future<void> _onImportPressed(BuildContext context) async {
     unawaited(
       showDialog(
         barrierDismissible: false,

app/lib/widget/dynamic_album_browser.dart

@@ -424,7 +424,7 @@ class _DynamicAlbumBrowserState extends State<DynamicAlbumBrowser>
     ).shareFiles(widget.account, selected);
   }
 
-  void _onSelectionDeletePressed() async {
+  Future<void> _onSelectionDeletePressed() async {
     SnackBarManager().showSnackBar(
       SnackBar(
         content: Text(L10n.global()

app/lib/widget/home_albums.dart

@@ -437,7 +437,7 @@ class _HomeAlbumsState extends State<HomeAlbums>
     );
   }
 
-  void _onSortSelected(album_util.AlbumSort sort) async {
+  Future<void> _onSortSelected(album_util.AlbumSort sort) async {
     await Pref().setHomeAlbumsSort(sort.index);
     setState(() {
       _transformItems(_bloc.state.items);

app/lib/widget/person_browser.dart

@@ -421,7 +421,7 @@ class _PersonBrowserState extends State<PersonBrowser>
     );
   }
 
-  void _transformItems(List<Face> items) async {
+  Future<void> _transformItems(List<Face> items) async {
     final files = await PopulatePerson(_c)(widget.account, items);
     _backingFiles = files
         .sorted(compareFileDateTimeDescending)

app/lib/widget/root_picker.dart

@@ -52,7 +52,7 @@ class _RootPickerState extends State<RootPicker> {
     _initAccount();
   }
 
-  void _initAccount() async {
+  Future<void> _initAccount() async {
     final c = KiwiContainer().resolve<DiContainer>();
     final files = <File>[];
     for (final r in widget.account.roots) {

app/lib/widget/settings.dart

@@ -397,7 +397,7 @@ class _SettingsState extends State<Settings> {
     }
   }
 
-  void _onCaptureLogChanged(BuildContext context, bool value) async {
+  Future<void> _onCaptureLogChanged(BuildContext context, bool value) async {
     if (value) {
       final result = await showDialog<bool>(
         context: context,
@@ -1375,7 +1375,7 @@ class _ThemeSettingsState extends State<_ThemeSettings> {
     );
   }
 
-  void _onFollowSystemThemeChanged(bool value) async {
+  Future<void> _onFollowSystemThemeChanged(bool value) async {
     final oldValue = _isFollowSystemTheme;
     setState(() {
       _isFollowSystemTheme = value;
@@ -1394,7 +1394,7 @@ class _ThemeSettingsState extends State<_ThemeSettings> {
     }
   }
 
-  void _onUseBlackInDarkThemeChanged(BuildContext context, bool value) async {
+  Future<void> _onUseBlackInDarkThemeChanged(BuildContext context, bool value) async {
     final oldValue = _isUseBlackInDarkTheme;
     setState(() {
       _isUseBlackInDarkTheme = value;
@@ -1491,7 +1491,7 @@ class _MiscSettingsState extends State<_MiscSettings> {
     }
   }
 
-  void _onPhotosTabSortByNameChanged(bool value) async {
+  Future<void> _onPhotosTabSortByNameChanged(bool value) async {
     final oldValue = _isPhotosTabSortByName;
     setState(() {
       _isPhotosTabSortByName = value;

app/lib/widget/slideshow_viewer.dart

@@ -239,7 +239,7 @@ class _SlideshowViewerState extends State<SlideshowViewer>
     _setupSlideTransition(widget.startIndex);
   }
 
-  void _onSlideshowTick() async {
+  Future<void> _onSlideshowTick() async {
     if (!mounted) {
       return;
     }

app/lib/widget/trashbin_browser.dart

@@ -267,7 +267,7 @@ class _TrashbinBrowserState extends State<TrashbinBrowser>
     }
   }
 
-  void _onEmptyTrashPressed(BuildContext context) async {
+  Future<void> _onEmptyTrashPressed(BuildContext context) async {
     unawaited(
       showDialog(
         context: context,

app/lib/widget/trashbin_viewer.dart

@@ -156,7 +156,7 @@ class _TrashbinViewerState extends State<TrashbinViewer> {
     );
   }
 
-  void _onRestorePressed() async {
+  Future<void> _onRestorePressed() async {
     final file = widget.streamFiles[_viewerController.currentPage];
     _log.info("[_onRestorePressed] Restoring file: ${file.path}");
     SnackBarManager().showSnackBar(

app/lib/widget/video_viewer.dart

@@ -93,7 +93,7 @@ class _VideoViewerState extends State<VideoViewer>
     _controller.dispose();
   }
 
-  void _initController(String url) async {
+  Future<void> _initController(String url) async {
     try {
       _controller = VideoPlayerController.network(
         url,

app/lib/widget/viewer.dart

@@ -612,7 +612,7 @@ class _ViewerState extends State<Viewer>
     DownloadHandler().downloadFiles(widget.account, [file]);
   }
 
-  void _onDeletePressed(BuildContext context) async {
+  Future<void> _onDeletePressed(BuildContext context) async {
     final file = widget.streamFiles[_viewerController.currentPage];
     _log.info("[_onDeletePressed] Removing file: ${file.path}");
     final count = await RemoveSelectionHandler()(
@@ -626,7 +626,7 @@ class _ViewerState extends State<Viewer>
     }
   }
 
-  void _onSlideshowPressed() async {
+  Future<void> _onSlideshowPressed() async {
     final result = await showDialog<SlideshowConfig>(
       context: context,
       builder: (_) => SlideshowDialog(

app/lib/widget/viewer_detail_pane.dart

@@ -430,7 +430,7 @@ class _ViewerDetailPaneState extends State<ViewerDetailPane> {
     }
   }
 
-  void _onUnarchivePressed(BuildContext context) async {
+  Future<void> _onUnarchivePressed(BuildContext context) async {
     _log.info("[_onUnarchivePressed] Unarchive file: ${widget.file.path}");
     try {
       await NotifiedAction(