Make `forNullableType` even more lenient

drift/CHANGELOG.md

@@ -1,4 +1,4 @@
-## 2.0.2
+## 2.0.2+1
 
 - Revert the breaking change around `QueryRow.read` only returning non-nullable
   values now - it was causing issues with type inference in some cases.

drift/lib/src/runtime/types/mapping.dart

@@ -2,6 +2,7 @@ import 'dart:core';
 import 'dart:core' as core;
 import 'dart:typed_data';
 
+import 'package:collection/collection.dart';
 import 'package:convert/convert.dart';
 import 'package:meta/meta.dart';
 
@@ -182,8 +183,19 @@ class SqlTypes {
   }
 }
 
+/// In [DriftSqlType.forNullableType], we need to do an `is` check over
+/// `DriftSqlType<T>` with a potentially nullable `T`. Since `DriftSqlType` is
+/// defined with a non-nullable `T`, this is illegal.
+/// The non-nullable upper bound in [DriftSqlType] is generally useful, for
+/// instance because it works well with [SqlTypes.read] which can then have a
+/// sound nullable return type.
+///
+/// As a hack, we define this base class that doesn't have this restriction and
+/// use this one for type checks.
+abstract class _InternalDriftSqlType<T> {}
+
 /// An enumation of type mappings that are builtin to drift and `drift_dev`.
-enum DriftSqlType<T extends Object> {
+enum DriftSqlType<T extends Object> implements _InternalDriftSqlType<T> {
   /// A boolean type, represented as `0` or `1` (int) in SQL.
   bool<core.bool>(),
 
@@ -282,12 +294,16 @@ enum DriftSqlType<T extends Object> {
   /// Using [forType] should pretty much always be preferred over this method,
   /// this one just exists for backwards compatibility.
   static DriftSqlType forNullableType<Dart>() {
-    final type = _dartToDrift[Dart];
+    // Lookup the type in the map first for faster lookups. Go back to a full
+    // typecheck where that doesn't work (which can be the case for complex
+    // type like `forNullableType<FutureOr<int?>>`).
+    final type = _dartToDrift[Dart] ??
+        values.whereType<_InternalDriftSqlType<Dart>>().singleOrNull;
 
     if (type == null) {
       throw ArgumentError('Could not find a matching SQL type for $Dart');
     }
 
-    return type;
+    return type as DriftSqlType;
   }
 }

drift/pubspec.yaml

@@ -1,6 +1,6 @@
 name: drift
 description: Drift is a reactive library to store relational data in Dart and Flutter applications.
-version: 2.0.2
+version: 2.0.2+1
 repository: https://github.com/simolus3/drift
 homepage: https://drift.simonbinder.eu/
 issue_tracker: https://github.com/simolus3/drift/issues

drift/test/integration_tests/regress_1991_test.dart

@@ -0,0 +1,34 @@
+import 'package:drift/drift.dart' hide isNotNull, isNull;
+import 'package:test/test.dart';
+
+import '../generated/todos.dart';
+import '../test_utils/test_utils.dart';
+
+// Regression test for https://github.com/simolus3/drift/issues/1991
+
+Future<int?> _getCategoryIdByDescription(
+    TodoDb appDatabase, String description) async {
+  const q = "SELECT id FROM categories WHERE desc = ?";
+  final row = await appDatabase.customSelect(
+    q,
+    variables: [Variable<String>(description)],
+  ).getSingleOrNull();
+  return row?.read("id");
+}
+
+void main() {
+  test('type inference for nullable call in async function', () async {
+    final db = TodoDb.connect(testInMemoryDatabase());
+    addTearDown(db.close);
+
+    final categoryDescription = 'category description';
+    expect(await _getCategoryIdByDescription(db, categoryDescription), isNull);
+
+    await db.categories.insertOne(
+        CategoriesCompanion.insert(description: categoryDescription));
+
+    // Search the category we just inserted
+    expect(
+        await _getCategoryIdByDescription(db, categoryDescription), isNotNull);
+  });
+}