Add MigrationRequiredException (#1459)

* Add MigrationRequiredException

* Re-include the error code in the error message

CHANGELOG.md

@@ -24,6 +24,7 @@
   ```
 
   The map keys may not contain `.` or start with `$`. (Issue [#685](https://github.com/realm/realm-dart/issues/685))
+* Added a new exception - `MigrationRequiredException` that will be thrown when a local Realm is opened with a schema that differs from the schema on disk and no migration callback is supplied. Additionally, a `helpLink` property has been added to `RealmException` and its subclasses to provide a link to the documentation for the error. (Issue [#1448](https://github.com/realm/realm-dart/issues/1448))
 
 ### Fixed
 * Fixed warnings being emitted by the realm generator requesting that `xyz.g.dart` be included with `part 'xyz.g.dart';` for `xyz.dart` files that import `realm` but don't have realm models defined. Those should not need generated parts and including the part file would have resulted in an empty file with `// ignore_for_file: type=lint` being generated. (PR [#1443](https://github.com/realm/realm-dart/pull/1443))

lib/src/native/realm_core.dart

@@ -154,7 +154,13 @@ class _RealmCore {
         throw UserCallbackException(lastError!.userError!);
       }
 
-      throw RealmException('${errorMessage != null ? "$errorMessage. " : ""}${lastError ?? ""}');
+      final message = '${errorMessage != null ? "$errorMessage. " : ""}${lastError ?? ""}';
+      switch (lastError?.code) {
+        case realm_errno.RLM_ERR_SCHEMA_MISMATCH:
+          throw MigrationRequiredException(message);
+        default:
+          throw RealmException(message);
+      }
     });
   }
 
@@ -694,7 +700,8 @@ class _RealmCore {
       if (error != nullptr) {
         final err = arena<realm_error>();
         bool success = _realmLib.realm_get_async_error(error, err);
-        completer.completeError(RealmException("Failed to open realm ${success ? err.ref.toLastError().toString() : ''}"));
+        final lastError = success ? err.ref.toLastError() : null;
+        completer.completeError(RealmException("Failed to open realm${lastError?.message ?? ''}"));
         return;
       }
 
@@ -2888,9 +2895,7 @@ class LastError {
   LastError(this.code, [this.message, this.userError]);
 
   @override
-  String toString() {
-    return "Error code: $code ${(message != null ? ". Message: $message" : "")}";
-  }
+  String toString() => "${message ?? 'No message'}. Error code: $code.";
 }
 
 // Flag to enable trace on finalization.

lib/src/realm_object.dart

@@ -582,14 +582,30 @@ extension RealmObjectInternal on RealmObjectBase {
 class RealmException implements Exception {
   final String message;
 
-  RealmException(this.message);
+  /// A link to the documentation that explains how to resolve the error.
+  final String? helpLink;
+
+  RealmException(this.message, {this.helpLink});
 
   @override
   String toString() {
     return "RealmException: $message";
   }
 }
 
+/// An exception thrown when a Realm is opened with a different schema and a migration is required.
+/// See [LocalConfiguration.migrationCallback] for more details.
+class MigrationRequiredException extends RealmException {
+  MigrationRequiredException(String message)
+      : super(message,
+            helpLink: "https://www.mongodb.com/docs/realm/sdk/flutter/realm-database/model-data/update-realm-object-schema/#manually-migrate-schema");
+
+  @override
+  String toString() {
+    return "Migration required: $message. See $helpLink for more details.";
+  }
+}
+
 /// An exception throws during execution of a user callback - e.g. during migration or initial data population.
 /// {@category Realm}
 class UserCallbackException extends RealmException {

test/app_test.dart

@@ -19,9 +19,7 @@
 import 'dart:convert';
 import 'dart:io';
 import 'dart:isolate';
-import 'dart:math';
 import 'package:logging/logging.dart';
-import 'package:meta/meta.dart';
 import 'package:test/expect.dart' hide throws;
 import 'package:path/path.dart' as path;
 import 'package:crypto/crypto.dart';
@@ -294,7 +292,7 @@ Future<void> main([List<String>? args]) async {
     expect(app.currentUser, user2);
     expect(
       () => app.switchUser(user1),
-      throws<RealmException>("Switch user failed. Error code: 4101 . Message: User is no longer valid or is logged out"),
+      throws<RealmException>("Switch user failed. User is no longer valid or is logged out"),
     );
   });
 

test/migration_test.dart

@@ -109,7 +109,11 @@ Future<void> main([List<String>? args]) async {
       invoked = true;
     });
 
-    expect(() => getRealm(config2), throws<RealmException>('Migration is required due to the following errors'));
+    expect(
+        () => getRealm(config2),
+        throwsA(isA<MigrationRequiredException>()
+            .having((e) => e.message, 'message', contains('Migration is required due to the following errors'))
+            .having((e) => e.helpLink, 'helpLink', isNotNull)));
     expect(invoked, false);
   });