color [nfc]: Add/use extension with argbInt, replacing deprecated value

The `value` getter is deprecated in flutter/engine@eff1b76cf (rolled
in flutter/flutter@8c1a93508), and I think that's because it could
lose precision for colors in different color spaces that are now
possible to represent. We're about to bump the Flutter minimum
version to take that change.

We're happy with the color space we've been using (sRGB), and this
integer representation has been helpful for us. So, add an extension
for it, allowing consumers to keep using it without each one needing a
`deprecated_member_use`.

Author: chrisbobbe

lib/notifications/display.dart

@@ -15,6 +15,7 @@ import '../model/binding.dart';
 import '../model/localizations.dart';
 import '../model/narrow.dart';
 import '../widgets/app.dart';
+import '../widgets/color.dart';
 import '../widgets/message_list.dart';
 import '../widgets/page.dart';
 import '../widgets/store.dart';
@@ -151,7 +152,7 @@ class NotificationDisplayManager {
       channelId: NotificationChannelManager.kChannelId,
       groupKey: groupKey,
 
-      color: kZulipBrandColor.value,
+      color: kZulipBrandColor.argbInt,
       // TODO vary notification icon for debug
       smallIconResourceName: 'zulip_notification', // This name must appear in keep.xml too: https://github.com/zulip/zulip-flutter/issues/528
 
@@ -193,7 +194,7 @@ class NotificationDisplayManager {
       groupKey: groupKey,
       isGroupSummary: true,
 
-      color: kZulipBrandColor.value,
+      color: kZulipBrandColor.argbInt,
       // TODO vary notification icon for debug
       smallIconResourceName: 'zulip_notification', // This name must appear in keep.xml too: https://github.com/zulip/zulip-flutter/issues/528
       inboxStyle: InboxStyle(

lib/widgets/channel_colors.dart

@@ -209,7 +209,7 @@ class ChannelColorSwatch extends ColorSwatch<ChannelColorVariant> {
         swatch = a._swatch.map((key, color) => MapEntry(key, Color.lerp(color, b[key], t)!));
       }
     }
-    return ChannelColorSwatch._(Color.lerp(a, b, t)!.value, swatch);
+    return ChannelColorSwatch._(Color.lerp(a, b, t)!.argbInt, swatch);
   }
 }
 

lib/widgets/color.dart

@@ -16,3 +16,26 @@ Color clampLchLightness(Color color, num lowerLimit, num upperLimit) {
     .copyWith(lightness: asLab.lightness.clamp(lowerLimit, upperLimit))
     .toColor();
 }
+
+extension ColorExtension on Color {
+  /// A 32 bit integer representing this sRGB color.
+  ///
+  /// If [colorSpace] is not [ColorSpace.sRGB], do not use this.
+  ///
+  /// The bits are assigned as follows:
+  ///
+  /// * Bits 24-31 are the alpha value.
+  /// * Bits 16-23 are the red value.
+  /// * Bits 8-15 are the green value.
+  /// * Bits 0-7 are the blue value.
+  ///
+  /// This is the same form that [Color.new] takes.
+  int get argbInt {
+    assert(colorSpace == ColorSpace.sRGB);
+
+    return ((a * 255.0).round() & 0xff) << 24 |
+           ((r * 255.0).round() & 0xff) << 16 |
+           ((g * 255.0).round() & 0xff) << 8 |
+           ((b * 255.0).round() & 0xff) << 0;
+  }
+}

test/notifications/display_test.dart

@@ -20,6 +20,7 @@ import 'package:zulip/model/store.dart';
 import 'package:zulip/notifications/display.dart';
 import 'package:zulip/notifications/receive.dart';
 import 'package:zulip/widgets/app.dart';
+import 'package:zulip/widgets/color.dart';
 import 'package:zulip/widgets/inbox.dart';
 import 'package:zulip/widgets/message_list.dart';
 import 'package:zulip/widgets/page.dart';
@@ -183,7 +184,7 @@ void main() {
               ..conversationTitle.equals(expectedTitle)
               ..messages.deepEquals(messageStyleMessagesChecks))
             ..number.equals(messageStyleMessages.length)
-            ..color.equals(kZulipBrandColor.value)
+            ..color.equals(kZulipBrandColor.argbInt)
             ..smallIconResourceName.equals('zulip_notification')
             ..extras.which((it) => it.isNotNull()
               ..deepEquals(<String, String>{
@@ -203,7 +204,7 @@ void main() {
             ..channelId.equals(NotificationChannelManager.kChannelId)
             ..contentTitle.isNull()
             ..contentText.isNull()
-            ..color.equals(kZulipBrandColor.value)
+            ..color.equals(kZulipBrandColor.argbInt)
             ..smallIconResourceName.equals('zulip_notification')
             ..extras.isNull()
             ..groupKey.equals(expectedGroupKey)

test/widgets/color_test.dart

@@ -0,0 +1,18 @@
+import 'dart:ui';
+
+import 'package:checks/checks.dart';
+import 'package:test/scaffolding.dart';
+import 'package:zulip/widgets/color.dart';
+
+void main() {
+  group('ColorExtension', () {
+    test('argbInt smoke', () {
+      const testCases = [
+        0xffffffff, 0x00000000, 0x12345678, 0x87654321, 0xfedcba98, 0x89abcdef];
+
+      for (final testCase in testCases) {
+        check(Color(testCase).argbInt).equals(testCase);
+      }
+    });
+  });
+}

test/widgets/inbox_test.dart

@@ -4,6 +4,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:zulip/api/model/events.dart';
 import 'package:zulip/api/model/model.dart';
 import 'package:zulip/model/store.dart';
+import 'package:zulip/widgets/color.dart';
 import 'package:zulip/widgets/icons.dart';
 import 'package:zulip/widgets/inbox.dart';
 import 'package:zulip/widgets/channel_colors.dart';
@@ -470,7 +471,7 @@ void main() {
         });
 
         testWidgets('uncollapsed header changes background color when [subscription.color] changes', (tester) async {
-          final initialColor = Colors.indigo.value;
+          final initialColor = Colors.indigo.argbInt;
 
           final stream = eg.stream(streamId: 1);
           await setupPage(tester,
@@ -483,7 +484,7 @@ void main() {
           check(streamHeaderBackgroundColor(tester, 1))
             .equals(ChannelColorSwatch.light(initialColor).barBackground);
 
-          final newColor = Colors.orange.value;
+          final newColor = Colors.orange.argbInt;
           store.handleEvent(SubscriptionUpdateEvent(id: 1, streamId: 1,
             property: SubscriptionProperty.color, value: newColor));
           await tester.pump();

test/widgets/message_list_test.dart

@@ -15,6 +15,7 @@ import 'package:zulip/model/localizations.dart';
 import 'package:zulip/model/narrow.dart';
 import 'package:zulip/model/store.dart';
 import 'package:zulip/widgets/autocomplete.dart';
+import 'package:zulip/widgets/color.dart';
 import 'package:zulip/widgets/content.dart';
 import 'package:zulip/widgets/emoji_reaction.dart';
 import 'package:zulip/widgets/icons.dart';
@@ -755,7 +756,7 @@ void main() {
       });
 
       testWidgets('color of recipient header background', (tester) async {
-        final subscription = eg.subscription(stream, color: Colors.red.value);
+        final subscription = eg.subscription(stream, color: Colors.red.argbInt);
         final swatch = ChannelColorSwatch.light(subscription.color);
         await setupMessageListPage(tester,
           messages: [eg.streamMessage(stream: subscription)],
@@ -770,7 +771,7 @@ void main() {
 
       testWidgets('color of stream icon', (tester) async {
         final stream = eg.stream(isWebPublic: true);
-        final subscription = eg.subscription(stream, color: Colors.red.value);
+        final subscription = eg.subscription(stream, color: Colors.red.argbInt);
         final swatch = ChannelColorSwatch.light(subscription.color);
         await setupMessageListPage(tester,
           messages: [eg.streamMessage(stream: subscription)],

test/widgets/subscription_list_test.dart

@@ -3,6 +3,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:zulip/api/model/initial_snapshot.dart';
 import 'package:zulip/api/model/model.dart';
+import 'package:zulip/widgets/color.dart';
 import 'package:zulip/widgets/icons.dart';
 import 'package:zulip/widgets/channel_colors.dart';
 import 'package:zulip/widgets/subscription_list.dart';
@@ -232,7 +233,7 @@ void main() {
     final unreadMsgs = eg.unreadMsgs(channels: [
       UnreadChannelSnapshot(streamId: stream.streamId, topic: 'a', unreadMessageIds: [1, 2]),
     ]);
-    final subscription = eg.subscription(stream, color: Colors.red.value);
+    final subscription = eg.subscription(stream, color: Colors.red.argbInt);
     final swatch = ChannelColorSwatch.light(subscription.color);
     await setupStreamListPage(tester, subscriptions: [
       subscription,