migrate use_build_context_synchronously integration test (dart-lang…

…/linter#4611)

* migrate `use_build_context_synchronously` integration test

* +doc

test/integration_test.dart

@@ -18,8 +18,6 @@ import 'integration/avoid_web_libraries_in_flutter.dart'
     as avoid_web_libraries_in_flutter;
 import 'integration/close_sinks.dart' as close_sinks;
 import 'integration/public_member_api_docs.dart' as public_member_api_docs;
-import 'integration/use_build_context_synchronously.dart'
-    as use_build_context_synchronously;
 import 'mocks.dart';
 import 'test_constants.dart';
 
@@ -128,7 +126,6 @@ void ruleTests() {
     avoid_web_libraries_in_flutter.main();
     close_sinks.main();
     public_member_api_docs.main();
-    use_build_context_synchronously.main();
   });
 }
 

test/rules/use_build_context_synchronously_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/src/test_utilities/find_node.dart';
+import 'package:analyzer/src/utilities/legacy.dart';
 import 'package:linter/src/rules/use_build_context_synchronously.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
@@ -14,6 +15,7 @@ main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(AsyncStateTest);
     defineReflectiveTests(UseBuildContextSynchronouslyTest);
+    defineReflectiveTests(UseBuildContextSynchronouslyMixedModeTest);
   });
 }
 
@@ -1630,6 +1632,52 @@ void foo(BuildContext context) async {
   }
 }
 
+@reflectiveTest
+class UseBuildContextSynchronouslyMixedModeTest extends LintRuleTest {
+  @override
+  bool get addFlutterPackageDep => true;
+
+  @override
+  String get lintRule => 'use_build_context_synchronously';
+
+  /// Ensure we're not run in the test dir.
+  @override
+  String get testPackageRootPath => '$workspaceRootPath/lib';
+
+  @override
+  setUp() {
+    super.setUp();
+    noSoundNullSafety = false;
+  }
+
+  tearDown() {
+    noSoundNullSafety = true;
+  }
+
+  /// https://github.com/dart-lang/linter/issues/2572
+  test_mixedMode() async {
+    newFile('$testPackageLibPath/migrated.dart', '''
+import 'package:flutter/widgets.dart';
+
+BuildContext? get contextOrNull => null;
+
+void f(BuildContext? contextOrNull) {}
+''');
+
+    await assertNoDiagnostics(r'''
+// @dart=2.9
+
+import 'migrated.dart';
+
+void nullableContext() async {
+  f(contextOrNull);
+  await Future<void>.delayed(Duration());
+  f(contextOrNull);
+}
+''');
+  }
+}
+
 @reflectiveTest
 class UseBuildContextSynchronouslyTest extends LintRuleTest {
   @override