diff --git a/test/vm_tests/builder/over_react_builder_test.dart b/test/vm_tests/builder/over_react_builder_test.dart
index df99e7cb0..237ace541 100644
--- a/test/vm_tests/builder/over_react_builder_test.dart
+++ b/test/vm_tests/builder/over_react_builder_test.dart
@@ -112,6 +112,28 @@ main() {
             'over_react|test_fixtures/source_files/backwards_compatible/basic_library.over_react.g.dart',
             '${p.absolute(p.current)}/test_fixtures/gold_output_files/backwards_compatible/basic_library.over_react.g.dart.goldFile');
       });
+
+      test('builds for props mixins', () async {
+        await checkBuildForFile(
+            'over_react|test_fixtures/source_files/backwards_compatible/props_mixin.dart',
+            'over_react|test_fixtures/source_files/backwards_compatible/props_mixin.over_react.g.dart',
+            '${p.absolute(p.current)}/test_fixtures/gold_output_files/backwards_compatible/props_mixin.over_react.g.dart.goldFile');
+      });
+
+      test('builds for state mixins', () async {
+        await checkBuildForFile(
+            'over_react|test_fixtures/source_files/backwards_compatible/state_mixin.dart',
+            'over_react|test_fixtures/source_files/backwards_compatible/state_mixin.over_react.g.dart',
+            '${p.absolute(p.current)}/test_fixtures/gold_output_files/backwards_compatible/state_mixin.over_react.g.dart.goldFile');
+      });
+
+      test('does not produce a build output for just a part file', () async {
+        var basicAsset = makeAssetId('over_react|test_fixtures/source_files/backwards_compatible/part_of_basic_library.dart');
+        await runBuilder(builder, [basicAsset], reader, writerSpy, AnalyzerResolvers(), logger: logger);
+
+        expect(writerSpy.assetsWritten, isEmpty);
+        verifyNoErrorLogs();
+      });
     });
 
     group('for Dart 2 only compatible boilerplate:', () {
@@ -119,28 +141,28 @@ main() {
         await checkBuildForFile(
             'over_react|test_fixtures/source_files/dart2_only/basic.dart',
             'over_react|test_fixtures/source_files/dart2_only/basic.over_react.g.dart',
-            '${p.absolute(p.current)}/test_fixtures/gold_output_files/basic.over_react.g.dart.goldFile');
+            '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/basic.over_react.g.dart.goldFile');
       });
 
       test('builds from basic multi-part library', () async {
         await checkBuildForFile(
             'over_react|test_fixtures/source_files/dart2_only/basic_library.dart',
             'over_react|test_fixtures/source_files/dart2_only/basic_library.over_react.g.dart',
-            '${p.absolute(p.current)}/test_fixtures/gold_output_files/basic_library.over_react.g.dart.goldFile');
+            '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/basic_library.over_react.g.dart.goldFile');
       });
 
       test('builds for props mixins', () async {
         await checkBuildForFile(
             'over_react|test_fixtures/source_files/dart2_only/props_mixin.dart',
             'over_react|test_fixtures/source_files/dart2_only/props_mixin.over_react.g.dart',
-            '${p.absolute(p.current)}/test_fixtures/gold_output_files/props_mixin.over_react.g.dart.goldFile');
+            '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/props_mixin.over_react.g.dart.goldFile');
       });
 
       test('builds for state mixins', () async {
         await checkBuildForFile(
             'over_react|test_fixtures/source_files/dart2_only/state_mixin.dart',
             'over_react|test_fixtures/source_files/dart2_only/state_mixin.over_react.g.dart',
-            '${p.absolute(p.current)}/test_fixtures/gold_output_files/state_mixin.over_react.g.dart.goldFile');
+            '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/state_mixin.over_react.g.dart.goldFile');
       });
 
       test('does not produce a build output for just a part file', () async {
@@ -161,20 +183,19 @@ main() {
             reason: 'Expected a SEVERE log for the missing over_react part.');
       });
 
-
       group('for Component2:', () {
         test('builds from basic component file', () async {
           await checkBuildForFile(
               'over_react|test_fixtures/source_files/dart2_only/component2/basic.dart',
               'over_react|test_fixtures/source_files/dart2_only/component2/basic.over_react.g.dart',
-              '${p.absolute(p.current)}/test_fixtures/gold_output_files/component2/basic.over_react.g.dart.goldFile');
+              '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/component2/basic.over_react.g.dart.goldFile');
         });
 
         test('builds from basic multi-part library', () async {
           await checkBuildForFile(
               'over_react|test_fixtures/source_files/dart2_only/component2/basic_library.dart',
               'over_react|test_fixtures/source_files/dart2_only/component2/basic_library.over_react.g.dart',
-              '${p.absolute(p.current)}/test_fixtures/gold_output_files/component2/basic_library.over_react.g.dart.goldFile');
+              '${p.absolute(p.current)}/test_fixtures/gold_output_files/dart2_only/component2/basic_library.over_react.g.dart.goldFile');
         });
       });
     });
diff --git a/test_fixtures/gold_output_files/README.md b/test_fixtures/gold_output_files/README.md
new file mode 100644
index 000000000..d44e8a763
--- /dev/null
+++ b/test_fixtures/gold_output_files/README.md
@@ -0,0 +1,11 @@
+## Updating golds
+
+To re-generate the gold files in this directory using the over_react builder, run:
+```sh
+dart tool/update_gold_output_files.dart
+```
+
+If that deletes other generated files throughout over_react (which usually only happens after it prompts you about conflicting outputs), you can restore them by running a build: 
+```sh
+dart run build_runner build
+```
diff --git a/test_fixtures/gold_output_files/backwards_compatible/props_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/backwards_compatible/props_mixin.over_react.g.dart.goldFile
new file mode 100644
index 000000000..7e4282250
--- /dev/null
+++ b/test_fixtures/gold_output_files/backwards_compatible/props_mixin.over_react.g.dart.goldFile
@@ -0,0 +1,78 @@
+//@dart=2.11
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+// ignore_for_file: deprecated_member_use_from_same_package, unnecessary_null_in_if_null_operators, prefer_null_aware_operators
+part of 'props_mixin.dart';
+
+// **************************************************************************
+// OverReactBuilder (package:over_react/src/builder.dart)
+// **************************************************************************
+
+abstract class $ExamplePropsMixinClass implements ExamplePropsMixinClass {
+  @override
+  Map get props;
+
+  static const PropsMeta meta = _$metaForExamplePropsMixinClass;
+
+  /// <!-- Generated from [ExamplePropsMixinClass.propMixin1] -->
+  @override
+  String get propMixin1 =>
+      (props[_$key__propMixin1__ExamplePropsMixinClass] ?? null) as String;
+
+  /// <!-- Generated from [ExamplePropsMixinClass.propMixin1] -->
+  @override
+  set propMixin1(String value) =>
+      props[_$key__propMixin1__ExamplePropsMixinClass] = value;
+  /* GENERATED CONSTANTS */
+  static const PropDescriptor _$prop__propMixin1__ExamplePropsMixinClass =
+      PropDescriptor(_$key__propMixin1__ExamplePropsMixinClass);
+  static const String _$key__propMixin1__ExamplePropsMixinClass =
+      'ExamplePropsMixinClass.propMixin1';
+
+  static const List<PropDescriptor> $props = [
+    _$prop__propMixin1__ExamplePropsMixinClass
+  ];
+  static const List<String> $propKeys = [
+    _$key__propMixin1__ExamplePropsMixinClass
+  ];
+}
+
+const PropsMeta _$metaForExamplePropsMixinClass = PropsMeta(
+  fields: $ExamplePropsMixinClass.$props,
+  keys: $ExamplePropsMixinClass.$propKeys,
+);
+
+abstract class $MixesInOtherMixinMixin<T extends Iterable, U>
+    implements MixesInOtherMixinMixin<T, U> {
+  @override
+  Map get props;
+
+  static const PropsMeta meta = _$metaForMixesInOtherMixinMixin;
+
+  /// <!-- Generated from [MixesInOtherMixinMixin.otherPropMixin] -->
+  @override
+  String get otherPropMixin =>
+      (props[_$key__otherPropMixin__MixesInOtherMixinMixin] ?? null) as String;
+
+  /// <!-- Generated from [MixesInOtherMixinMixin.otherPropMixin] -->
+  @override
+  set otherPropMixin(String value) =>
+      props[_$key__otherPropMixin__MixesInOtherMixinMixin] = value;
+  /* GENERATED CONSTANTS */
+  static const PropDescriptor _$prop__otherPropMixin__MixesInOtherMixinMixin =
+      PropDescriptor(_$key__otherPropMixin__MixesInOtherMixinMixin);
+  static const String _$key__otherPropMixin__MixesInOtherMixinMixin =
+      'MixesInOtherMixinMixin.otherPropMixin';
+
+  static const List<PropDescriptor> $props = [
+    _$prop__otherPropMixin__MixesInOtherMixinMixin
+  ];
+  static const List<String> $propKeys = [
+    _$key__otherPropMixin__MixesInOtherMixinMixin
+  ];
+}
+
+const PropsMeta _$metaForMixesInOtherMixinMixin = PropsMeta(
+  fields: $MixesInOtherMixinMixin.$props,
+  keys: $MixesInOtherMixinMixin.$propKeys,
+);
diff --git a/test_fixtures/gold_output_files/backwards_compatible/state_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/backwards_compatible/state_mixin.over_react.g.dart.goldFile
new file mode 100644
index 000000000..894e12e73
--- /dev/null
+++ b/test_fixtures/gold_output_files/backwards_compatible/state_mixin.over_react.g.dart.goldFile
@@ -0,0 +1,43 @@
+//@dart=2.11
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+// ignore_for_file: deprecated_member_use_from_same_package, unnecessary_null_in_if_null_operators, prefer_null_aware_operators
+part of 'state_mixin.dart';
+
+// **************************************************************************
+// OverReactBuilder (package:over_react/src/builder.dart)
+// **************************************************************************
+
+abstract class $ExampleStateMixinClass implements ExampleStateMixinClass {
+  @override
+  Map get state;
+
+  static const StateMeta meta = _$metaForExampleStateMixinClass;
+
+  /// <!-- Generated from [ExampleStateMixinClass.stateMixin1] -->
+  @override
+  String get stateMixin1 =>
+      (state[_$key__stateMixin1__ExampleStateMixinClass] ?? null) as String;
+
+  /// <!-- Generated from [ExampleStateMixinClass.stateMixin1] -->
+  @override
+  set stateMixin1(String value) =>
+      state[_$key__stateMixin1__ExampleStateMixinClass] = value;
+  /* GENERATED CONSTANTS */
+  static const StateDescriptor _$prop__stateMixin1__ExampleStateMixinClass =
+      StateDescriptor(_$key__stateMixin1__ExampleStateMixinClass);
+  static const String _$key__stateMixin1__ExampleStateMixinClass =
+      'ExampleStateMixinClass.stateMixin1';
+
+  static const List<StateDescriptor> $state = [
+    _$prop__stateMixin1__ExampleStateMixinClass
+  ];
+  static const List<String> $stateKeys = [
+    _$key__stateMixin1__ExampleStateMixinClass
+  ];
+}
+
+const StateMeta _$metaForExampleStateMixinClass = StateMeta(
+  fields: $ExampleStateMixinClass.$state,
+  keys: $ExampleStateMixinClass.$stateKeys,
+);
diff --git a/test_fixtures/gold_output_files/basic.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/basic.over_react.g.dart.goldFile
similarity index 100%
rename from test_fixtures/gold_output_files/basic.over_react.g.dart.goldFile
rename to test_fixtures/gold_output_files/dart2_only/basic.over_react.g.dart.goldFile
diff --git a/test_fixtures/gold_output_files/basic_library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/basic_library.over_react.g.dart.goldFile
similarity index 100%
rename from test_fixtures/gold_output_files/basic_library.over_react.g.dart.goldFile
rename to test_fixtures/gold_output_files/dart2_only/basic_library.over_react.g.dart.goldFile
diff --git a/test_fixtures/gold_output_files/component2/basic.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/component2/basic.over_react.g.dart.goldFile
similarity index 100%
rename from test_fixtures/gold_output_files/component2/basic.over_react.g.dart.goldFile
rename to test_fixtures/gold_output_files/dart2_only/component2/basic.over_react.g.dart.goldFile
diff --git a/test_fixtures/gold_output_files/component2/basic_library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/component2/basic_library.over_react.g.dart.goldFile
similarity index 100%
rename from test_fixtures/gold_output_files/component2/basic_library.over_react.g.dart.goldFile
rename to test_fixtures/gold_output_files/dart2_only/component2/basic_library.over_react.g.dart.goldFile
diff --git a/test_fixtures/gold_output_files/dart2_only/missing_over_react_g_part/library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/missing_over_react_g_part/library.over_react.g.dart.goldFile
new file mode 100644
index 000000000..cf674ce48
--- /dev/null
+++ b/test_fixtures/gold_output_files/dart2_only/missing_over_react_g_part/library.over_react.g.dart.goldFile
@@ -0,0 +1,116 @@
+//@dart=2.11
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+// ignore_for_file: deprecated_member_use_from_same_package, unnecessary_null_in_if_null_operators, prefer_null_aware_operators
+part of 'library.dart';
+
+// **************************************************************************
+// OverReactBuilder (package:over_react/src/builder.dart)
+// **************************************************************************
+
+// React component factory implementation.
+//
+// Registers component implementation and links type meta to builder factory.
+final $BasicPartOfLibComponentFactory = registerComponent(
+  () => _$BasicPartOfLibComponent(),
+  builderFactory: _$BasicPartOfLib,
+  componentClass: BasicPartOfLibComponent,
+  isWrapper: false,
+  parentType: null,
+);
+
+abstract class _$BasicPartOfLibPropsAccessorsMixin
+    implements _$BasicPartOfLibProps {
+  @override
+  Map get props;
+
+  /// <!-- Generated from [_$BasicPartOfLibProps.basicProp] -->
+  @override
+  String get basicProp =>
+      (props[_$key__basicProp___$BasicPartOfLibProps] ?? null) as String;
+
+  /// <!-- Generated from [_$BasicPartOfLibProps.basicProp] -->
+  @override
+  set basicProp(String value) =>
+      props[_$key__basicProp___$BasicPartOfLibProps] = value;
+  /* GENERATED CONSTANTS */
+  static const PropDescriptor _$prop__basicProp___$BasicPartOfLibProps =
+      PropDescriptor(_$key__basicProp___$BasicPartOfLibProps);
+  static const String _$key__basicProp___$BasicPartOfLibProps =
+      'BasicPartOfLibProps.basicProp';
+
+  static const List<PropDescriptor> $props = [
+    _$prop__basicProp___$BasicPartOfLibProps
+  ];
+  static const List<String> $propKeys = [
+    _$key__basicProp___$BasicPartOfLibProps
+  ];
+}
+
+const PropsMeta _$metaForBasicPartOfLibProps = PropsMeta(
+  fields: _$BasicPartOfLibPropsAccessorsMixin.$props,
+  keys: _$BasicPartOfLibPropsAccessorsMixin.$propKeys,
+);
+
+class BasicPartOfLibProps extends _$BasicPartOfLibProps
+    with _$BasicPartOfLibPropsAccessorsMixin {
+  static const PropsMeta meta = _$metaForBasicPartOfLibProps;
+}
+
+_$$BasicPartOfLibProps _$BasicPartOfLib([Map backingProps]) =>
+    _$$BasicPartOfLibProps(backingProps);
+
+// Concrete props implementation.
+//
+// Implements constructor and backing map, and links up to generated component factory.
+class _$$BasicPartOfLibProps extends _$BasicPartOfLibProps
+    with _$BasicPartOfLibPropsAccessorsMixin
+    implements BasicPartOfLibProps {
+  // This initializer of `_props` to an empty map, as well as the reassignment
+  // of `_props` in the constructor body is necessary to work around a DDC bug: https://github.com/dart-lang/sdk/issues/36217
+  _$$BasicPartOfLibProps(Map backingMap) : this._props = {} {
+    this._props = backingMap ?? {};
+  }
+
+  /// The backing props map proxied by this class.
+  @override
+  Map get props => _props;
+  Map _props;
+
+  /// Let `UiProps` internals know that this class has been generated.
+  @override
+  bool get $isClassGenerated => true;
+
+  /// The `ReactComponentFactory` associated with the component built by this class.
+  @override
+  ReactComponentFactoryProxy get componentFactory =>
+      super.componentFactory ?? $BasicPartOfLibComponentFactory;
+
+  /// The default namespace for the prop getters/setters generated for this class.
+  @override
+  String get propKeyNamespace => 'BasicPartOfLibProps.';
+}
+
+// Concrete component implementation mixin.
+//
+// Implements typed props/state factories, defaults `consumedPropKeys` to the keys
+// generated for the associated props class.
+class _$BasicPartOfLibComponent extends BasicPartOfLibComponent {
+  @override
+  _$$BasicPartOfLibProps typedPropsFactory(Map backingMap) =>
+      _$$BasicPartOfLibProps(backingMap);
+
+  /// Let `UiComponent` internals know that this class has been generated.
+  @override
+  bool get $isClassGenerated => true;
+
+  @override
+  String get displayName => 'BasicPartOfLib';
+
+  /// The default consumed props, taken from _$BasicPartOfLibProps.
+  /// Used in `*ConsumedProps` methods if [consumedProps] is not overridden.
+  @override
+  final List<ConsumedProps> $defaultConsumedProps = const [
+    _$metaForBasicPartOfLibProps
+  ];
+}
diff --git a/test_fixtures/gold_output_files/props_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/props_mixin.over_react.g.dart.goldFile
similarity index 100%
rename from test_fixtures/gold_output_files/props_mixin.over_react.g.dart.goldFile
rename to test_fixtures/gold_output_files/dart2_only/props_mixin.over_react.g.dart.goldFile
diff --git a/test_fixtures/gold_output_files/state_mixin.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/dart2_only/state_mixin.over_react.g.dart.goldFile
similarity index 100%
rename from test_fixtures/gold_output_files/state_mixin.over_react.g.dart.goldFile
rename to test_fixtures/gold_output_files/dart2_only/state_mixin.over_react.g.dart.goldFile
diff --git a/test_fixtures/gold_output_files/mixin_based/missing_over_react_g_part/library.over_react.g.dart.goldFile b/test_fixtures/gold_output_files/mixin_based/missing_over_react_g_part/library.over_react.g.dart.goldFile
new file mode 100644
index 000000000..196a98a3f
--- /dev/null
+++ b/test_fixtures/gold_output_files/mixin_based/missing_over_react_g_part/library.over_react.g.dart.goldFile
@@ -0,0 +1,188 @@
+//@dart=2.11
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+// ignore_for_file: deprecated_member_use_from_same_package, unnecessary_null_in_if_null_operators, prefer_null_aware_operators
+part of 'library.dart';
+
+// **************************************************************************
+// OverReactBuilder (package:over_react/src/builder.dart)
+// **************************************************************************
+
+// React component factory implementation.
+//
+// Registers component implementation and links type meta to builder factory.
+@Deprecated('This API is for use only within generated code.'
+    ' Do not reference it in your code, as it may change at any time.')
+final $BasicPartOfLibComponentFactory = registerComponent2(
+  () => _$BasicPartOfLibComponent(),
+  builderFactory: _$BasicPartOfLib,
+  componentClass: BasicPartOfLibComponent,
+  isWrapper: false,
+  parentType: null,
+);
+
+_$$BasicPartOfLibProps _$BasicPartOfLib([Map backingProps]) =>
+    backingProps == null
+        ? _$$BasicPartOfLibProps$JsMap(JsBackedMap())
+        : _$$BasicPartOfLibProps(backingProps);
+
+// Concrete props implementation.
+//
+// Implements constructor and backing map, and links up to generated component factory.
+@Deprecated('This API is for use only within generated code.'
+    ' Do not reference it in your code, as it may change at any time.')
+abstract class _$$BasicPartOfLibProps extends UiProps
+    with
+        BasicPartOfLibProps,
+        // If this generated mixin is undefined, it's likely because BasicPartOfLibProps is not a valid `mixin`-based props mixin, or because it is but the generated mixin was not imported. Check the declaration of BasicPartOfLibProps, and check that $BasicPartOfLibProps is exported/imported properly.
+        $BasicPartOfLibProps {
+  _$$BasicPartOfLibProps._();
+
+  factory _$$BasicPartOfLibProps(Map backingMap) {
+    if (backingMap == null || backingMap is JsBackedMap) {
+      return _$$BasicPartOfLibProps$JsMap(backingMap as JsBackedMap);
+    } else {
+      return _$$BasicPartOfLibProps$PlainMap(backingMap);
+    }
+  }
+
+  /// Let `UiProps` internals know that this class has been generated.
+  @override
+  bool get $isClassGenerated => true;
+
+  /// The `ReactComponentFactory` associated with the component built by this class.
+  @override
+  ReactComponentFactoryProxy get componentFactory =>
+      super.componentFactory ?? $BasicPartOfLibComponentFactory;
+
+  /// The default namespace for the prop getters/setters generated for this class.
+  @override
+  String get propKeyNamespace => '';
+
+  @override
+  PropsMetaCollection get staticMeta => const PropsMetaCollection({
+        // If this generated mixin is undefined, it's likely because BasicPartOfLibProps is not a valid `mixin`-based props mixin, or because it is but the generated mixin was not imported. Check the declaration of BasicPartOfLibProps, and check that $BasicPartOfLibProps is exported/imported properly.
+        BasicPartOfLibProps: $BasicPartOfLibProps.meta,
+      });
+}
+
+// Concrete props implementation that can be backed by any [Map].
+@Deprecated('This API is for use only within generated code.'
+    ' Do not reference it in your code, as it may change at any time.')
+class _$$BasicPartOfLibProps$PlainMap extends _$$BasicPartOfLibProps {
+  // This initializer of `_props` to an empty map, as well as the reassignment
+  // of `_props` in the constructor body is necessary to work around a DDC bug: https://github.com/dart-lang/sdk/issues/36217
+  _$$BasicPartOfLibProps$PlainMap(Map backingMap)
+      : this._props = {},
+        super._() {
+    this._props = backingMap ?? {};
+  }
+
+  /// The backing props map proxied by this class.
+  @override
+  Map get props => _props;
+  Map _props;
+}
+
+// Concrete props implementation that can only be backed by [JsMap],
+// allowing dart2js to compile more optimal code for key-value pair reads/writes.
+@Deprecated('This API is for use only within generated code.'
+    ' Do not reference it in your code, as it may change at any time.')
+class _$$BasicPartOfLibProps$JsMap extends _$$BasicPartOfLibProps {
+  // This initializer of `_props` to an empty map, as well as the reassignment
+  // of `_props` in the constructor body is necessary to work around a DDC bug: https://github.com/dart-lang/sdk/issues/36217
+  _$$BasicPartOfLibProps$JsMap(JsBackedMap backingMap)
+      : this._props = JsBackedMap(),
+        super._() {
+    this._props = backingMap ?? JsBackedMap();
+  }
+
+  /// The backing props map proxied by this class.
+  @override
+  JsBackedMap get props => _props;
+  JsBackedMap _props;
+}
+
+// Concrete component implementation mixin.
+//
+// Implements typed props/state factories, defaults `consumedPropKeys` to the keys
+// generated for the associated props class.
+@Deprecated('This API is for use only within generated code.'
+    ' Do not reference it in your code, as it may change at any time.')
+class _$BasicPartOfLibComponent extends BasicPartOfLibComponent {
+  _$$BasicPartOfLibProps$JsMap _cachedTypedProps;
+
+  @override
+  _$$BasicPartOfLibProps$JsMap get props => _cachedTypedProps;
+
+  @override
+  set props(Map value) {
+    assert(
+        getBackingMap(value) is JsBackedMap,
+        'Component2.props should never be set directly in '
+        'production. If this is required for testing, the '
+        'component should be rendered within the test. If '
+        'that does not have the necessary result, the last '
+        'resort is to use typedPropsFactoryJs.');
+    super.props = value;
+    _cachedTypedProps =
+        typedPropsFactoryJs(getBackingMap(value) as JsBackedMap);
+  }
+
+  @override
+  _$$BasicPartOfLibProps$JsMap typedPropsFactoryJs(JsBackedMap backingMap) =>
+      _$$BasicPartOfLibProps$JsMap(backingMap);
+
+  @override
+  _$$BasicPartOfLibProps typedPropsFactory(Map backingMap) =>
+      _$$BasicPartOfLibProps(backingMap);
+
+  /// Let `UiComponent` internals know that this class has been generated.
+  @override
+  bool get $isClassGenerated => true;
+
+  @override
+  String get displayName => 'BasicPartOfLib';
+
+  /// The default consumed props, comprising all props mixins used by BasicPartOfLibProps.
+  /// Used in `*ConsumedProps` methods if [consumedProps] is not overridden.
+  @override
+  get $defaultConsumedProps => propsMeta.all;
+
+  @override
+  PropsMetaCollection get propsMeta => const PropsMetaCollection({
+        // If this generated mixin is undefined, it's likely because BasicPartOfLibProps is not a valid `mixin`-based props mixin, or because it is but the generated mixin was not imported. Check the declaration of BasicPartOfLibProps, and check that $BasicPartOfLibProps is exported/imported properly.
+        BasicPartOfLibProps: $BasicPartOfLibProps.meta,
+      });
+}
+
+@Deprecated('This API is for use only within generated code.'
+    ' Do not reference it in your code, as it may change at any time.'
+    ' EXCEPTION: this may be used in legacy boilerplate until'
+    ' it is transitioned to the new mixin-based boilerplate.')
+mixin $BasicPartOfLibProps on BasicPartOfLibProps {
+  static const PropsMeta meta = _$metaForBasicPartOfLibProps;
+  @override
+  String get basicProp =>
+      (props[_$key__basicProp__BasicPartOfLibProps] ?? null) as String;
+  @override
+  set basicProp(String value) =>
+      props[_$key__basicProp__BasicPartOfLibProps] = value;
+  /* GENERATED CONSTANTS */
+  static const PropDescriptor _$prop__basicProp__BasicPartOfLibProps =
+      PropDescriptor(_$key__basicProp__BasicPartOfLibProps);
+  static const String _$key__basicProp__BasicPartOfLibProps =
+      'BasicPartOfLibProps.basicProp';
+
+  static const List<PropDescriptor> $props = [
+    _$prop__basicProp__BasicPartOfLibProps
+  ];
+  static const List<String> $propKeys = [_$key__basicProp__BasicPartOfLibProps];
+}
+
+@Deprecated('This API is for use only within generated code.'
+    ' Do not reference it in your code, as it may change at any time.')
+const PropsMeta _$metaForBasicPartOfLibProps = PropsMeta(
+  fields: $BasicPartOfLibProps.$props,
+  keys: $BasicPartOfLibProps.$propKeys,
+);
diff --git a/test_fixtures/gold_output_files/mixin_based/two_nine_with_multiple_factories.over_react.g.dart.goldfile b/test_fixtures/gold_output_files/mixin_based/two_nine_with_multiple_factories.over_react.g.dart.goldfile
index 3ca3afaab..7176ed98b 100644
--- a/test_fixtures/gold_output_files/mixin_based/two_nine_with_multiple_factories.over_react.g.dart.goldfile
+++ b/test_fixtures/gold_output_files/mixin_based/two_nine_with_multiple_factories.over_react.g.dart.goldfile
@@ -148,7 +148,7 @@ class _$CounterComponent extends CounterComponent {
   bool get $isClassGenerated => true;
 
   @override
-  String get displayName => 'Counter';
+  String get displayName => '_Counter';
 
   /// The default consumed props, comprising all props mixins used by CounterProps.
   /// Used in `*ConsumedProps` methods if [consumedProps] is not overridden.
diff --git a/tool/update_gold_output_files.dart b/tool/update_gold_output_files.dart
new file mode 100644
index 000000000..1e15b4d07
--- /dev/null
+++ b/tool/update_gold_output_files.dart
@@ -0,0 +1,58 @@
+import 'dart:io';
+
+import 'package:glob/glob.dart';
+import 'package:glob/list_local_fs.dart';
+import 'package:path/path.dart' as p;
+
+final sourceFixturesDir = Directory('test_fixtures/source_files');
+final goldsDir = Directory('test_fixtures/gold_output_files');
+
+/// A temporary directory used to generate new golds.
+final tmpSourceDir = Directory('test/tmp_test_files');
+
+/// Updates gold files in [goldsDir] by re-generating them from a copy of the files in [sourceFixturesDir].
+Future<void> main() async {
+  print('Copying files from ${sourceFixturesDir.path} to temporary directory ${tmpSourceDir.path}');
+  if (tmpSourceDir.existsSync()) tmpSourceDir.deleteSync(recursive: true);
+  tmpSourceDir.createSync(recursive: true);
+  for (final file in Glob(p.join(sourceFixturesDir.path, '**')).listSync().whereType<File>()) {
+    final newPath = p.join(tmpSourceDir.path, p.relative(file.path, from: sourceFixturesDir.path));
+    File(newPath).parent.createSync(recursive: true);
+    file.copySync(newPath);
+  }
+
+  print('Building files in temporary directory ${tmpSourceDir.path}');
+  final buildProcess = await Process.start(
+      'dart', ['run', 'build_runner', 'build', '--build-filter=${p.join(tmpSourceDir.path, '**')}'],
+      mode: ProcessStartMode.inheritStdio);
+  // Wait for build to complete.
+  final buildExitCode = await buildProcess.exitCode;
+  if (buildExitCode != 0) {
+    stderr.writeln(
+        '^ Build failures are expected for "missing_over_react_g_part" files, and can be ignored.');
+  }
+
+  print('Copying built files to golds directory ${goldsDir.path}');
+  final generatedTmpFiles =
+      Glob(p.join(tmpSourceDir.path, '**.over_react.g.dart')).listSync().whereType<File>().toList();
+  if (generatedTmpFiles.isEmpty) {
+    throw Exception('No generated files were found in ${tmpSourceDir.path}.'
+        ' Ensure in build.yaml the over_react builder runs on directory with build_to:source');
+  }
+  for (final file in generatedTmpFiles) {
+    final newPath =
+        p.join(goldsDir.path, p.relative(file.path, from: tmpSourceDir.path)) + '.goldFile';
+    File(newPath).parent.createSync(recursive: true);
+    file.copySync(newPath);
+  }
+
+  print('Cleaning up temporary directory ${tmpSourceDir.path}');
+  tmpSourceDir.deleteSync(recursive: true);
+
+  print('Done!');
+
+  print('\nIf non-gold generated files throughout this package got deleted'
+      ' (which usually only happens after it prompts you about conflicting outputs),'
+      ' you can restore them by running a build:\n\n'
+      '    dart run build_runner build');
+}