[dartdevc] Resetting lazy js types on hot restart

Fixes https://github.com/flutter/flutter/issues/66361

Change-Id: I4e68963a36c71bb4dac964d8b0fdcd8ee9187e97
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/164101
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Mark Zhou <markzipan@google.com>

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/runtime.dart

@@ -179,8 +179,8 @@ final List<Object> _cacheMaps = JS('!', '[]');
 /// A list of functions to reset static fields back to their uninitialized
 /// state.
 ///
-/// This is populated by [defineLazyField], and only contains the list of fields
-/// that have actually been initialized.
+/// This is populated by [defineLazyField] and [LazyJSType] and only contains
+/// fields that have been initialized.
 @notNull
 final List<void Function()> _resetFields = JS('', '[]');
 

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/types.dart

@@ -177,7 +177,7 @@ F tearoffInterop<F extends Function?>(F f) {
 /// we disable type checks for in these cases, and allow any JS object to work
 /// as if it were an instance of this JS type.
 class LazyJSType extends DartType {
-  Function()? _getRawJSTypeFn;
+  Function() _getRawJSTypeFn;
   @notNull
   final String _dartName;
   Object? _rawJSType;
@@ -199,14 +199,14 @@ class LazyJSType extends DartType {
     // overhead, especially if exceptions are being thrown. Also it means the
     // behavior of a given type check can change later on.
     try {
-      raw = _getRawJSTypeFn!();
+      raw = _getRawJSTypeFn();
     } catch (e) {}
 
     if (raw == null) {
       _warn('Cannot find native JavaScript type ($_dartName) for type check');
     } else {
       _rawJSType = raw;
-      _getRawJSTypeFn = null; // Free the function that computes the JS type.
+      JS('', '#.push(() => # = null)', _resetFields, _rawJSType);
     }
     return raw;
   }

tests/dartdevc/hot_restart_js_interop_test.dart

@@ -0,0 +1,51 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Tests that JS interop works with hot restart.
+
+// Requirements=nnbd
+
+@JS()
+library hot_restart_js_interop_test;
+
+import 'dart:js' show context;
+import 'dart:js_util';
+import 'dart:_foreign_helper' as helper show JS;
+import 'dart:_runtime' as dart;
+
+import 'package:expect/expect.dart';
+import 'package:js/js.dart';
+
+@JS()
+external void eval(String code);
+
+@JS('window.MyClass')
+class MyClass {
+  external MyClass();
+}
+
+abstract class Wrapper<T> {
+  T? rawObject;
+
+  Wrapper() {
+    final T defaultObject = createDefault();
+    rawObject = defaultObject;
+  }
+
+  T createDefault();
+}
+
+class WrappedClass extends Wrapper<MyClass> {
+  @override
+  MyClass createDefault() => MyClass();
+}
+
+void main() {
+  // See: https://github.com/flutter/flutter/issues/66361
+  eval("self.MyClass = function MyClass() {}");
+  var c = WrappedClass();
+  dart.hotRestart();
+  eval("self.MyClass = function MyClass() {}");
+  c = WrappedClass();
+}