unread_count_badge [nfc]: Remove extra API for specific background color

Previously, this widget had three options for the background color:

1. Colorized for a channel: callers could pass a ChannelColorSwatch,
   and the implementation would pick `unreadCountBadgeBackground` off
   of that.
2. Any `Color`.
3. A default, chosen by the implementation.

One caller was using option 2 when option 1 would be a better fit:
it wanted a channel-colored background, but it was picking
`unreadCountBadgeBackground` itself from the ChannelColorSwatch
instead of letting the implementation do that.

After changing that caller to just pass the ChannelColorSwatch
(option 1), no more callers use option 2, so we remove it. Now
UnreadCountBadge has a tighter interface.

Next we'll encapsulate finding the channel color swatch itself, so
callers only need to have a channel ID if they want a
channel-colored background.

Author: chrisbobbe

lib/widgets/inbox.dart

@@ -6,6 +6,7 @@ import '../model/narrow.dart';
 import '../model/recent_dm_conversations.dart';
 import '../model/unreads.dart';
 import 'action_sheet.dart';
+import 'channel_colors.dart';
 import 'icons.dart';
 import 'message_list.dart';
 import 'page.dart';
@@ -249,7 +250,7 @@ abstract class _HeaderItem extends StatelessWidget {
   Color collapsedIconColor(BuildContext context);
   Color uncollapsedIconColor(BuildContext context);
   Color uncollapsedBackgroundColor(BuildContext context);
-  Color? unreadCountBadgeBackgroundColor(BuildContext context);
+  ChannelColorSwatch? unreadCountBadgeBackgroundColor(BuildContext context);
 
   Future<void> onCollapseButtonTap() async {
     if (!collapsed) {
@@ -332,7 +333,7 @@ class _AllDmsHeaderItem extends _HeaderItem {
   @override Color uncollapsedIconColor(context) => DesignVariables.of(context).labelMenuButton;
 
   @override Color uncollapsedBackgroundColor(context) => DesignVariables.of(context).dmHeaderBg;
-  @override Color? unreadCountBadgeBackgroundColor(context) => null;
+  @override ChannelColorSwatch? unreadCountBadgeBackgroundColor(context) => null;
 
   @override Future<void> onCollapseButtonTap() async {
     await super.onCollapseButtonTap();
@@ -462,7 +463,7 @@ class _StreamHeaderItem extends _HeaderItem with _LongPressable {
     colorSwatchFor(context, subscription).iconOnBarBackground;
   @override Color uncollapsedBackgroundColor(context) =>
     colorSwatchFor(context, subscription).barBackground;
-  @override Color? unreadCountBadgeBackgroundColor(context) =>
+  @override ChannelColorSwatch? unreadCountBadgeBackgroundColor(context) =>
     colorSwatchFor(context, subscription);
 
   @override Future<void> onCollapseButtonTap() async {

lib/widgets/unread_count_badge.dart

@@ -19,21 +19,19 @@ class UnreadCountBadge extends StatelessWidget {
   final int count;
   final bool bold;
 
-  /// The badge's background color.
+  /// An optional [ChannelColorSwatch], to override the default color scheme
+  /// with a channel-colorized one.
   ///
-  /// Pass a [ChannelColorSwatch] if this badge represents messages in one
-  /// specific stream. The appropriate color from the swatch will be used.
-  ///
-  /// If null, the default neutral background will be used.
-  final Color? backgroundColor;
+  /// Pass this if the badge represents messages in one specific stream.
+  /// The appropriate color from the swatch will be used.
+  final ChannelColorSwatch? backgroundColor;
 
   @override
   Widget build(BuildContext context) {
     final designVariables = DesignVariables.of(context);
 
     final effectiveBackgroundColor = switch (backgroundColor) {
       ChannelColorSwatch(unreadCountBadgeBackground: var color) => color,
-      Color() => backgroundColor,
       null => designVariables.bgCounterUnread,
     };
 

test/widgets/unread_count_badge_test.dart

@@ -22,7 +22,7 @@ void main() {
     });
 
     group('background', () {
-      Future<void> prepare(WidgetTester tester, Color? backgroundColor) async {
+      Future<void> prepare(WidgetTester tester, ChannelColorSwatch? backgroundColor) async {
         addTearDown(testBinding.reset);
         await tester.pumpWidget(TestZulipApp(
           child: UnreadCountBadge(count: 1, backgroundColor: backgroundColor)));
@@ -40,11 +40,6 @@ void main() {
         check(findBackgroundColor(tester)).isNotNull().isSameColorAs(const Color(0x26666699));
       });
 
-      testWidgets('specified color', (tester) async {
-        await prepare(tester, Colors.pink);
-        check(findBackgroundColor(tester)).isNotNull().isSameColorAs(Colors.pink);
-      });
-
       testWidgets('stream color', (tester) async {
         final swatch = ChannelColorSwatch.light(0xff76ce90);
         await prepare(tester, swatch);