[html] Fix nested JS Map to Dart assignment

Added check to convertNativeToDart_Dictionary to recursively convert native objects within a map to their Dart equivalent.

Fixes: https://github.com/dart-lang/sdk/issues/44319
Change-Id: I80a2bc0541454900b1c7d9635debaf72d7c120f2
Bug: 44319
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/201200
Commit-Queue: Gabriel Castro <gabrielmcastro@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Srujan Gaddam <srujzs@google.com>

CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ### Core libraries
 
+### `dart:html`
+
+* [#44319][]: `convertNativeToDart_Dictionary()` now converts objects
+  recursively, this fixes APIs like MediaStreamTrack.getCapabilities
+  that convert between Maps and browser Dictionaries.
+
+[44319]: (https://github.com/dart-lang/sdk/issues/44319)
+
 #### `dart:async`
 
 * The uncaught error handlers of `Zone`s are now run in the parent zone

sdk/lib/html/html_common/conversions_dart2js.dart

@@ -1,14 +1,36 @@
 part of html_common;
 
-/// Converts a JavaScript object with properties into a Dart Map.
-/// Not suitable for nested objects.
+/// Converts native values to their Dart equivalent
+///
+/// This includes other maps, lists, or values that don't need a conversion e.g.
+/// bool, String.
+_convertNativeToDart_Value(value) {
+  if (value == null) return value;
+  if (value is String || value is num || value is bool) return value;
+  if (isJavaScriptSimpleObject(value)) {
+    return convertNativeToDart_Dictionary(value);
+  }
+  if (JS('bool', 'Array.isArray(#)', value)) {
+    List values = [];
+    for (var i = 0; i < JS<int>('int', '#.length', value); i++) {
+      values.add(_convertNativeToDart_Value(JS('var', '#[#]', value, i)));
+    }
+
+    return values;
+  }
+  return value;
+}
+
+/// Recursively converts a JavaScript object with properties into a Dart Map.
+/// This includes maps, lists, and other values that don't need a conversion.
 Map<String, dynamic>? convertNativeToDart_Dictionary(object) {
   if (object == null) return null;
   var dict = <String, dynamic>{};
   var keys = JS<JSExtendableArray>(
       'JSExtendableArray', 'Object.getOwnPropertyNames(#)', object);
   for (final key in keys) {
-    dict[key] = JS('var', '#[#]', object, key);
+    dict[JS('String', '#', key)] =
+        _convertNativeToDart_Value(JS('var', '#[#]', object, key));
   }
   return dict;
 }

tests/lib/html/convert_native_to_dart_dictionary_test.dart

@@ -0,0 +1,36 @@
+// Copyright (c) 2021, 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.
+
+import 'dart:html_common';
+import 'package:expect/expect.dart';
+import 'package:expect/minitest.dart';
+
+var obj = {
+  'val1': 'hello',
+  'val2': 'there',
+  'val3': {
+    'sub1': 'general kenobi',
+    'sub2': 'you are',
+    'sub3': 'a bold one',
+    'sub4': {
+      'nilval': null,
+      'boolval': false,
+    }
+  },
+  'val4': [
+    'execute',
+    'order',
+    '66',
+    {'number': 33}
+  ]
+};
+
+main() {
+  test('dart to native -> native to dart', () {
+    var toNative = convertDartToNative_Dictionary(obj);
+    var toDart = convertNativeToDart_Dictionary(toNative);
+
+    Expect.deepEquals(obj, toDart);
+  });
+}

tests/lib_2/html/convert_native_to_dart_dictionary_test.dart

@@ -0,0 +1,36 @@
+// Copyright (c) 2021, 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.
+
+import 'dart:html_common';
+import 'package:expect/expect.dart';
+import 'package:expect/minitest.dart';
+
+var obj = {
+  'val1': 'hello',
+  'val2': 'there',
+  'val3': {
+    'sub1': 'general kenobi',
+    'sub2': 'you are',
+    'sub3': 'a bold one',
+    'sub4': {
+      'nilval': null,
+      'boolval': false,
+    }
+  },
+  'val4': [
+    'execute',
+    'order',
+    '66',
+    {'number': 33}
+  ]
+};
+
+main() {
+  test('dart to native -> native to dart', () {
+    var toNative = convertDartToNative_Dictionary(obj);
+    var toDart = convertNativeToDart_Dictionary(toNative);
+
+    Expect.deepEquals(obj, toDart);
+  });
+}