treewide: Container -> SizedBox.shrink()

This helps performance without any user-facing changes,
since SizedBox is constant while Container isn't

lib/pages/chat/chat_app_bar_title.dart

@@ -17,7 +17,7 @@ class ChatAppBarTitle extends StatelessWidget {
   Widget build(BuildContext context) {
     final room = controller.room;
     if (room == null) {
-      return Container();
+      return const SizedBox.shrink();
     }
     if (controller.selectedEvents.isNotEmpty) {
       return Text(controller.selectedEvents.length.toString());

lib/pages/chat/chat_event_list.dart

@@ -91,7 +91,7 @@ class ChatEventList extends StatelessWidget {
                 ),
               );
             }
-            return Container();
+            return const SizedBox.shrink();
           }
 
           // The message at this index:
@@ -127,7 +127,7 @@ class ChatEventList extends StatelessWidget {
                         ? controller.timeline!.events[i]
                         : null,
                   )
-                : Container(),
+                : const SizedBox.shrink(),
           );
         },
         childCount: controller.timeline!.events.length + 2,

lib/pages/chat/chat_input_row.dart

@@ -23,7 +23,7 @@ class ChatInputRow extends StatelessWidget {
   Widget build(BuildContext context) {
     if (controller.showEmojiPicker &&
         controller.emojiPickerType == EmojiPickerType.reaction) {
-      return Container();
+      return const SizedBox.shrink();
     }
     return Row(
       crossAxisAlignment: CrossAxisAlignment.end,
@@ -72,7 +72,7 @@ class ChatInputRow extends StatelessWidget {
                             ),
                           ),
                         )
-                  : Container(),
+                  : const SizedBox.shrink(),
             ]
           : <Widget>[
               KeyBoardShortcuts(

lib/pages/chat/events/message.dart

@@ -54,7 +54,7 @@ class Message extends StatelessWidget {
       EventTypes.CallInvite
     }.contains(event.type)) {
       if (event.type.startsWith('m.call.')) {
-        return Container();
+        return const SizedBox.shrink();
       }
       return StateMessage(event);
     }

lib/pages/chat/input_bar.dart

@@ -313,7 +313,7 @@ class InputBar extends StatelessWidget {
         ),
       );
     }
-    return Container();
+    return const SizedBox.shrink();
   }
 
   void insertSuggestion(_, Map<String, String?> suggestion) {
@@ -458,11 +458,11 @@ class InputBar extends StatelessWidget {
               buildSuggestion(c, s, Matrix.of(context).client),
           onSuggestionSelected: (Map<String, String?> suggestion) =>
               insertSuggestion(context, suggestion),
-          errorBuilder: (BuildContext context, Object? error) => Container(),
-          loadingBuilder: (BuildContext context) => Container(),
+          errorBuilder: (BuildContext context, Object? error) => const SizedBox.shrink(),
+          loadingBuilder: (BuildContext context) => const SizedBox.shrink(),
           // fix loading briefly flickering a dark box
           noItemsFoundBuilder: (BuildContext context) =>
-              Container(), // fix loading briefly showing no suggestions
+              const SizedBox.shrink(), // fix loading briefly showing no suggestions
         ),
       ),
     );

lib/pages/chat/pinned_events.dart

@@ -49,7 +49,7 @@ class PinnedEvents extends StatelessWidget {
     final pinnedEventIds = controller.room!.pinnedEventIds;
 
     if (pinnedEventIds.isEmpty) {
-      return Container();
+      return const SizedBox.shrink();
     }
     final completers = pinnedEventIds.map<Completer<Event?>>((e) {
       final completer = Completer<Event?>();

lib/pages/chat/reactions_picker.dart

@@ -15,7 +15,7 @@ class ReactionsPicker extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    if (controller.showEmojiPicker) return Container();
+    if (controller.showEmojiPicker) return const SizedBox.shrink();
     final display = controller.editEvent == null &&
         controller.replyEvent == null &&
         controller.room!.canSendDefaultMessages &&
@@ -29,7 +29,7 @@ class ReactionsPicker extends StatelessWidget {
         child: Builder(
           builder: (context) {
             if (!display) {
-              return Container();
+              return const SizedBox.shrink();
             }
             final proposals = proposeEmojis(
               controller.selectedEvents.first.plaintextBody,

lib/pages/chat/reply_display.dart

@@ -58,7 +58,7 @@ class _EditContent extends StatelessWidget {
   Widget build(BuildContext context) {
     final event = this.event;
     if (event == null) {
-      return Container();
+      return const SizedBox.shrink();
     }
     return Row(
       children: <Widget>[

lib/pages/chat/sticker_picker_dialog.dart

@@ -39,7 +39,7 @@ class StickerPickerDialogState extends State<StickerPickerDialog> {
       final imageKeys =
           filteredImagePackImageEntried.map((e) => e.key).toList();
       if (imageKeys.isEmpty) {
-        return Container();
+        return const SizedBox.shrink();
       }
       final packName = pack.pack.displayName ?? packSlugs[packIndex];
       return Column(

lib/pages/chat/tombstone_display.dart

@@ -12,7 +12,7 @@ class TombstoneDisplay extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     if (controller.room!.getState(EventTypes.RoomTombstone) == null) {
-      return Container();
+      return const SizedBox.shrink();
     }
     return SizedBox(
       height: 72,

lib/pages/chat_details/chat_details_view.dart

@@ -409,7 +409,7 @@ class ChatDetailsView extends StatelessWidget {
                                   ),
                                   onTap: () => VRouter.of(context).to('invite'),
                                 )
-                              : Container(),
+                              : const SizedBox.shrink(),
                         ],
                       )
                     : i < controller.members!.length + 1

lib/pages/chat_details/participant_list_item.dart

@@ -62,7 +62,7 @@ class ParticipantListItem extends StatelessWidget {
                 ),
               ),
             membershipBatch[user.membership]!.isEmpty
-                ? Container()
+                ? const SizedBox.shrink()
                 : Container(
                     padding: const EdgeInsets.all(4),
                     margin: const EdgeInsets.symmetric(horizontal: 8),

lib/pages/chat_list/chat_list_body.dart

@@ -227,7 +227,7 @@ class ChatListViewBody extends StatelessWidget {
                             .contains(
                               controller.searchController.text.toLowerCase(),
                             )) {
-                          return Container();
+                          return const SizedBox.shrink();
                         }
                         return ChatListItem(
                           rooms[i],

lib/pages/chat_list/chat_list_item.dart

@@ -326,7 +326,7 @@ class ChatListItem extends StatelessWidget {
                             fontSize: 13,
                           ),
                         )
-                      : Container(),
+                      : const SizedBox.shrink(),
                 ),
               ),
             ],

lib/pages/chat_list/client_chooser_button.dart

@@ -189,7 +189,7 @@ class ClientChooserButton extends StatelessWidget {
                 index,
                 context,
               ),
-              child: Container(),
+              child: const SizedBox.shrink(),
             ),
           ),
           KeyBoardShortcuts(
@@ -199,7 +199,7 @@ class ClientChooserButton extends StatelessWidget {
             },
             helpLabel: L10n.of(context)!.nextAccount,
             onKeysPressed: () => _nextAccount(matrix, context),
-            child: Container(),
+            child: const SizedBox.shrink(),
           ),
           KeyBoardShortcuts(
             keysToPress: {
@@ -209,7 +209,7 @@ class ClientChooserButton extends StatelessWidget {
             },
             helpLabel: L10n.of(context)!.previousAccount,
             onKeysPressed: () => _previousAccount(matrix, context),
-            child: Container(),
+            child: const SizedBox.shrink(),
           ),
           PopupMenuButton<Object>(
             onSelected: (o) => _clientSelected(o, context),

lib/pages/chat_list/stories_header.dart

@@ -121,7 +121,7 @@ class StoriesHeader extends StatelessWidget {
           final displayname = creator.calcDisplayname();
           final avatarUrl = creator.avatarUrl;
           if (!displayname.toLowerCase().contains(filter.toLowerCase())) {
-            return Container();
+            return const SizedBox.shrink();
           }
           return _StoryButton(
             profile: Profile(

lib/pages/settings_emotes/settings_emotes_view.dart

@@ -107,7 +107,7 @@ class EmotesSettingsView extends StatelessWidget {
                     )
                   : ListView.separated(
                       separatorBuilder: (BuildContext context, int i) =>
-                          Container(),
+                          const SizedBox.shrink(),
                       itemCount: imageKeys.length + 1,
                       itemBuilder: (BuildContext context, int i) {
                         if (i >= imageKeys.length) {

lib/pages/settings_multiple_emotes/settings_multiple_emotes_view.dart

@@ -35,7 +35,7 @@ class MultipleEmotesSettingsView extends StatelessWidget {
           final keys = packs.keys.toList();
           keys.sort();
           return ListView.separated(
-            separatorBuilder: (BuildContext context, int i) => Container(),
+            separatorBuilder: (BuildContext context, int i) => const SizedBox.shrink(),
             itemCount: keys.length,
             itemBuilder: (BuildContext context, int i) {
               final event = packs[keys[i]];

lib/pages/story/story_view.dart

@@ -207,7 +207,7 @@ class StoryView extends StatelessWidget {
                       final videoPlayerController = snapshot.data;
                       if (videoPlayerController == null) {
                         controller.loadingModeOn();
-                        return Container();
+                        return const SizedBox.shrink();
                       }
                       controller.loadingModeOff();
                       return Center(child: VideoPlayer(videoPlayerController));
@@ -226,7 +226,7 @@ class StoryView extends StatelessWidget {
                     final matrixFile = snapshot.data;
                     if (matrixFile == null) {
                       controller.loadingModeOn();
-                      return Container();
+                      return const SizedBox.shrink();
                     }
                     controller.loadingModeOff();
                     return Container(

lib/widgets/chat_settings_popup_menu.dart

@@ -115,7 +115,7 @@ class ChatSettingsPopupMenuState extends State<ChatSettingsPopupMenu> {
           },
           helpLabel: L10n.of(context)!.chatDetails,
           onKeysPressed: _showChatDetails,
-          child: Container(),
+          child: const SizedBox.shrink(),
         ),
         KeyBoardShortcuts(
           keysToPress: {
@@ -124,7 +124,7 @@ class ChatSettingsPopupMenuState extends State<ChatSettingsPopupMenu> {
           },
           helpLabel: L10n.of(context)!.matrixWidgets,
           onKeysPressed: _showWidgets,
-          child: Container(),
+          child: const SizedBox.shrink(),
         ),
         PopupMenuButton(
           onSelected: (String choice) async {

lib/widgets/mxc_image.dart

@@ -163,7 +163,7 @@ class _MxcImageState extends State<MxcImage> {
           data == null ? CrossFadeState.showFirst : CrossFadeState.showSecond,
       firstChild: placeholder(context),
       secondChild: data == null || data.isEmpty
-          ? Container()
+          ? const SizedBox.shrink()
           : Image.memory(
               data,
               width: widget.width,