Fix `computeWithDatabase` in transactions

drift/CHANGELOG.md

@@ -3,6 +3,7 @@
 - Don't keep databases in an unusable state if the `setup` callback throws an
   exception. Instead, drift will retry the next time the database is used.
 - Allow targeting partial indices in `DoUpdate` ([#2394](https://github.com/simolus3/drift/issues/2394))
+- Fix deadlocks when `computeWithDatabase` is called inside a `transaction()`.
 
 ## 2.7.0
 

drift/lib/isolate.dart

@@ -221,13 +221,17 @@ extension ComputeWithDriftIsolate<DB extends DatabaseConnectionUser> on DB {
   /// requiring a database is also available through [computeWithDatabase].
   @experimental
   Future<DriftIsolate> serializableConnection() async {
+    final currentlyInRootConnection = resolvedEngine is GeneratedDatabase;
     // ignore: invalid_use_of_protected_member
-    final localConnection = connection;
+    final localConnection = resolvedEngine.connection;
     final data = await localConnection.connectionData;
 
-    if (data is DriftIsolate) {
-      // The local database is already connected to an isolate, use that one
-      // directly.
+    // If we're connected to an isolate already, we can use that one directly
+    // instead of starting a short-lived drift server.
+    // However, this does not work if [serializableConnection] is called in a
+    // transaction zone, since the top-level connection could be blocked waiting
+    // for the transaction (as transactions can't be concurrent in sqlite3).
+    if (data is DriftIsolate && currentlyInRootConnection) {
       return data;
     } else {
       // Set up a drift server acting as a proxy to the existing database

drift/test/isolate_test.dart

@@ -199,6 +199,26 @@ void main() {
       // Make sure database still works after computeWithDatabase
       // https://github.com/simolus3/drift/issues/2279#issuecomment-1455385439
       await db.customSelect('SELECT 1').get();
+
+      // This should still work when computeWithDatabase is called in a
+      // transaction.
+      await db.transaction(() async {
+        await db.into(db.categories).insert(
+            CategoriesCompanion.insert(description: 'main / transaction'));
+
+        await db.computeWithDatabase(
+          computation: (db) async {
+            await db.batch((batch) {
+              batch.insert(
+                db.categories,
+                CategoriesCompanion.insert(description: 'nested remote batch!'),
+              );
+            });
+          },
+          connect: TodoDb.new,
+        );
+      });
+
       await db.close();
     }