api: Don't allow connecting to servers <4.0

assets/l10n/app_en.arb

@@ -447,6 +447,10 @@
   "@dialogClose": {
     "description": "Button label in dialogs to close."
   },
+  "errorDialogLearnMore": "Learn more",
+  "@errorDialogLearnMore": {
+    "description": "Button label in error dialogs to open a web page with more information."
+  },
   "errorDialogContinue": "OK",
   "@errorDialogContinue": {
     "description": "Button label in error dialogs to acknowledge the error and close the dialog."
@@ -534,6 +538,15 @@
   "@topicValidationErrorMandatoryButEmpty": {
     "description": "Topic validation error when topic is required but was empty."
   },
+  "errorServerVersionUnsupportedMessage": "{url} is running Zulip Server {zulipVersion}, which is unsupported. The minimum supported version is Zulip Server {minSupportedZulipVersion}.",
+  "@errorServerVersionUnsupportedMessage": {
+    "description": "Error message in the dialog for when the Zulip Server version is unsupported.",
+    "placeholders": {
+      "url": {"type": "String", "example": "http://chat.example.com/"},
+      "zulipVersion": {"type": "String", "example": "3.2"},
+      "minSupportedZulipVersion": {"type": "String", "example": "4.0"}
+    }
+  },
   "errorInvalidApiKeyMessage": "Your account at {url} could not be authenticated. Please try logging in again or use another account.",
   "@errorInvalidApiKeyMessage": {
     "description": "Error message in the dialog for invalid API key.",

lib/api/core.dart

@@ -10,6 +10,24 @@ import '../model/binding.dart';
 import '../model/localizations.dart';
 import 'exception.dart';
 
+/// The Zulip Server version below which we should refuse to connect.
+///
+/// When updating this, also update [kMinSupportedZulipFeatureLevel]
+/// and the README.
+const kMinSupportedZulipVersion = '4.0';
+
+/// The Zulip feature level reserved for the [kMinSupportedZulipVersion] release.
+///
+/// For this value, see the API changelog:
+///   https://zulip.com/api/changelog
+const kMinSupportedZulipFeatureLevel = 65;
+
+/// The doc stating our oldest supported server version.
+// TODO: Instead, link to new Help Center doc once we have it:
+//   https://github.com/zulip/zulip/issues/23842
+final kServerSupportDocUrl = Uri.parse(
+  'https://zulip.readthedocs.io/en/latest/overview/release-lifecycle.html#client-apps');
+
 /// A fused JSON + UTF-8 decoder.
 ///
 /// This object is an instance of [`_JsonUtf8Decoder`][1] which is

lib/generated/l10n/zulip_localizations.dart

@@ -693,6 +693,12 @@ abstract class ZulipLocalizations {
   /// **'Close'**
   String get dialogClose;
 
+  /// Button label in error dialogs to open a web page with more information.
+  ///
+  /// In en, this message translates to:
+  /// **'Learn more'**
+  String get errorDialogLearnMore;
+
   /// Button label in error dialogs to acknowledge the error and close the dialog.
   ///
   /// In en, this message translates to:
@@ -819,6 +825,12 @@ abstract class ZulipLocalizations {
   /// **'Topics are required in this organization.'**
   String get topicValidationErrorMandatoryButEmpty;
 
+  /// Error message in the dialog for when the Zulip Server version is unsupported.
+  ///
+  /// In en, this message translates to:
+  /// **'{url} is running Zulip Server {zulipVersion}, which is unsupported. The minimum supported version is Zulip Server {minSupportedZulipVersion}.'**
+  String errorServerVersionUnsupportedMessage(String url, String zulipVersion, String minSupportedZulipVersion);
+
   /// Error message in the dialog for invalid API key.
   ///
   /// In en, this message translates to:

lib/generated/l10n/zulip_localizations_ar.dart

@@ -348,6 +348,9 @@ class ZulipLocalizationsAr extends ZulipLocalizations {
   @override
   String get dialogClose => 'Close';
 
+  @override
+  String get errorDialogLearnMore => 'Learn more';
+
   @override
   String get errorDialogContinue => 'OK';
 
@@ -413,6 +416,11 @@ class ZulipLocalizationsAr extends ZulipLocalizations {
   @override
   String get topicValidationErrorMandatoryButEmpty => 'Topics are required in this organization.';
 
+  @override
+  String errorServerVersionUnsupportedMessage(String url, String zulipVersion, String minSupportedZulipVersion) {
+    return '$url is running Zulip Server $zulipVersion, which is unsupported. The minimum supported version is Zulip Server $minSupportedZulipVersion.';
+  }
+
   @override
   String errorInvalidApiKeyMessage(String url) {
     return 'Your account at $url could not be authenticated. Please try logging in again or use another account.';

lib/generated/l10n/zulip_localizations_en.dart

@@ -348,6 +348,9 @@ class ZulipLocalizationsEn extends ZulipLocalizations {
   @override
   String get dialogClose => 'Close';
 
+  @override
+  String get errorDialogLearnMore => 'Learn more';
+
   @override
   String get errorDialogContinue => 'OK';
 
@@ -413,6 +416,11 @@ class ZulipLocalizationsEn extends ZulipLocalizations {
   @override
   String get topicValidationErrorMandatoryButEmpty => 'Topics are required in this organization.';
 
+  @override
+  String errorServerVersionUnsupportedMessage(String url, String zulipVersion, String minSupportedZulipVersion) {
+    return '$url is running Zulip Server $zulipVersion, which is unsupported. The minimum supported version is Zulip Server $minSupportedZulipVersion.';
+  }
+
   @override
   String errorInvalidApiKeyMessage(String url) {
     return 'Your account at $url could not be authenticated. Please try logging in again or use another account.';

lib/generated/l10n/zulip_localizations_ja.dart

@@ -348,6 +348,9 @@ class ZulipLocalizationsJa extends ZulipLocalizations {
   @override
   String get dialogClose => 'Close';
 
+  @override
+  String get errorDialogLearnMore => 'Learn more';
+
   @override
   String get errorDialogContinue => 'OK';
 
@@ -413,6 +416,11 @@ class ZulipLocalizationsJa extends ZulipLocalizations {
   @override
   String get topicValidationErrorMandatoryButEmpty => 'Topics are required in this organization.';
 
+  @override
+  String errorServerVersionUnsupportedMessage(String url, String zulipVersion, String minSupportedZulipVersion) {
+    return '$url is running Zulip Server $zulipVersion, which is unsupported. The minimum supported version is Zulip Server $minSupportedZulipVersion.';
+  }
+
   @override
   String errorInvalidApiKeyMessage(String url) {
     return 'Your account at $url could not be authenticated. Please try logging in again or use another account.';

lib/generated/l10n/zulip_localizations_nb.dart

@@ -348,6 +348,9 @@ class ZulipLocalizationsNb extends ZulipLocalizations {
   @override
   String get dialogClose => 'Close';
 
+  @override
+  String get errorDialogLearnMore => 'Learn more';
+
   @override
   String get errorDialogContinue => 'OK';
 
@@ -413,6 +416,11 @@ class ZulipLocalizationsNb extends ZulipLocalizations {
   @override
   String get topicValidationErrorMandatoryButEmpty => 'Topics are required in this organization.';
 
+  @override
+  String errorServerVersionUnsupportedMessage(String url, String zulipVersion, String minSupportedZulipVersion) {
+    return '$url is running Zulip Server $zulipVersion, which is unsupported. The minimum supported version is Zulip Server $minSupportedZulipVersion.';
+  }
+
   @override
   String errorInvalidApiKeyMessage(String url) {
     return 'Your account at $url could not be authenticated. Please try logging in again or use another account.';

lib/generated/l10n/zulip_localizations_pl.dart

@@ -348,6 +348,9 @@ class ZulipLocalizationsPl extends ZulipLocalizations {
   @override
   String get dialogClose => 'Zamknij';
 
+  @override
+  String get errorDialogLearnMore => 'Learn more';
+
   @override
   String get errorDialogContinue => 'OK';
 
@@ -413,6 +416,11 @@ class ZulipLocalizationsPl extends ZulipLocalizations {
   @override
   String get topicValidationErrorMandatoryButEmpty => 'Wątki są wymagane przez tę organizację.';
 
+  @override
+  String errorServerVersionUnsupportedMessage(String url, String zulipVersion, String minSupportedZulipVersion) {
+    return '$url is running Zulip Server $zulipVersion, which is unsupported. The minimum supported version is Zulip Server $minSupportedZulipVersion.';
+  }
+
   @override
   String errorInvalidApiKeyMessage(String url) {
     return 'Konto w ramach $url nie zostało przyjęte. Spróbuj ponownie lub skorzystaj z innego konta.';

lib/generated/l10n/zulip_localizations_ru.dart

@@ -348,6 +348,9 @@ class ZulipLocalizationsRu extends ZulipLocalizations {
   @override
   String get dialogClose => 'Закрыть';
 
+  @override
+  String get errorDialogLearnMore => 'Learn more';
+
   @override
   String get errorDialogContinue => 'OK';
 
@@ -413,6 +416,11 @@ class ZulipLocalizationsRu extends ZulipLocalizations {
   @override
   String get topicValidationErrorMandatoryButEmpty => 'Темы обязательны в этой организации.';
 
+  @override
+  String errorServerVersionUnsupportedMessage(String url, String zulipVersion, String minSupportedZulipVersion) {
+    return '$url is running Zulip Server $zulipVersion, which is unsupported. The minimum supported version is Zulip Server $minSupportedZulipVersion.';
+  }
+
   @override
   String errorInvalidApiKeyMessage(String url) {
     return 'Your account at $url could not be authenticated. Please try logging in again or use another account.';

lib/generated/l10n/zulip_localizations_sk.dart

@@ -348,6 +348,9 @@ class ZulipLocalizationsSk extends ZulipLocalizations {
   @override
   String get dialogClose => 'Zavrieť';
 
+  @override
+  String get errorDialogLearnMore => 'Learn more';
+
   @override
   String get errorDialogContinue => 'OK';
 
@@ -413,6 +416,11 @@ class ZulipLocalizationsSk extends ZulipLocalizations {
   @override
   String get topicValidationErrorMandatoryButEmpty => 'Topics are required in this organization.';
 
+  @override
+  String errorServerVersionUnsupportedMessage(String url, String zulipVersion, String minSupportedZulipVersion) {
+    return '$url is running Zulip Server $zulipVersion, which is unsupported. The minimum supported version is Zulip Server $minSupportedZulipVersion.';
+  }
+
   @override
   String errorInvalidApiKeyMessage(String url) {
     return 'Your account at $url could not be authenticated. Please try logging in again or use another account.';

lib/log.dart

@@ -62,7 +62,11 @@ void profilePrint(String message) {
 // `null` for the `message` parameter and promptly dismiss the reported errors.
 typedef ReportErrorCancellablyCallback = void Function(String? message, {String? details});
 
-typedef ReportErrorCallback = void Function(String title, {String? message});
+typedef ReportErrorCallback = void Function(
+  String title, {
+  String? message,
+  Uri? learnMoreButtonUrl,
+});
 
 /// Show the user an error message, without requiring them to interact with it.
 ///
@@ -96,7 +100,11 @@ void defaultReportErrorToUserBriefly(String? message, {String? details}) {
   _reportErrorToConsole(message, details);
 }
 
-void defaultReportErrorToUserModally(String title, {String? message}) {
+void defaultReportErrorToUserModally(
+  String title, {
+  String? message,
+  Uri? learnMoreButtonUrl,
+}) {
   _reportErrorToConsole(title, message);
 }
 

lib/model/binding.dart

@@ -32,7 +32,7 @@ typedef FirebaseRemoteMessage = firebase_messaging.RemoteMessage;
 ///
 /// Most code should not interact with the bindings directly.
 /// Instead, use the corresponding higher-level APIs that expose the bindings'
-/// functionality in a widget-oriented way.
+/// functionality in a widget-oriented way; see [PlatformActions] for some.
 ///
 /// This piece of architecture is modelled on the "binding" classes in Flutter
 /// itself.  For discussion, see [BindingBase], [WidgetsFlutterBinding], and