title: Flutter failed to build build_runner with Freezed
body: <p>I am facing this issue when I added a new property to the Freezed class for the first time in three months, and then run</p>
  <p><code>flutter clean &amp;&amp; flutter pub get &amp;&amp; flutter pub run build_runner build --delete-conflicting-outputs</code>.</p>
  <p>And I tried the answers on the following page, but it did not solve the problem.</p>
  <p><a href="https://stackoverflow.com/questions/58023664/flutter-pub-run-build-runner-build-failed">flutter pub run build_runner build failed</a></p>
  <pre><code>flutter clean
  flutter pub cache repair
  flutter pub get
  flutter pub run build_runner clean
  flutter pub run build_runner build --delete-conflicting-outputs  
  </code></pre>
  <p>The following is my code before and after the change</p>
  
  <pre class="lang-Dart prettyprint-override"><code>//Before
  import 'package:freezed_annotation/freezed_annotation.dart';
  import 'package:~/models/item/item.dart';
  part 'user.freezed.dart';
  part 'user.g.dart';
  part 'user_controller.dart';
  @freezed
  abstract class User with _$User {
    const factory User({
      @Default('') String name,
      @Default(35.6620) double latitude,
      @Default(139.7038) double longitude,
    }) = _User;
    factory User.fromJson(Map&lt;String, dynamic&gt; json) =&gt; _$UserFromJson(json);
  }
  
  //After
  import 'package:cloud_firestore/cloud_firestore.dart';
  import 'package:freezed_annotation/freezed_annotation.dart';
  import 'package:~/models/item/item.dart';
  part 'user.freezed.dart';
  part 'user.g.dart';
  part 'user_controller.dart';
  @freezed
  abstract class User with _$User {
    const factory User({
      @Default('') String name,
      @Default(35.6620) double latitude,
      @Default(139.7038) double longitude,
      int age,
      @Default('') String birthday,
      @Default('') String gender,
      @Default('') String imageURL,
      @Default('') String introduction,
      @Default('') String restaurant,
      @DateTimeConverter() DateTime updateAt,
      @DateTimeConverter() DateTime createAt,
      @Default('') String uri,
    }) = _User;
    factory User.fromJson(Map&lt;String, dynamic&gt; json) =&gt; _$UserFromJson(json);
  }
  class DateTimeConverter implements JsonConverter&lt;DateTime, Timestamp&gt; {
    const DateTimeConverter();
    @override
    DateTime fromJson(Timestamp value) {
      return DateTime.parse(value.toDate().toString());
    }
    @override
    Timestamp toJson(DateTime value) =&gt; Timestamp.fromDate(value);
  }
  </code></pre>
  <p>The following is the error message</p>
  <pre class="lang-Dart prettyprint-override"><code>Running &quot;flutter pub get&quot; in my_code...                        2,962ms
  Failed to build build_runner:build_runner:
  ../../Developer/flutter/.pub-cache/hosted/pub.dartlang.org/analyzer-0.41.2/lib/src/error/best_practices_verifier.dart:258:50: Error: The property 'displayString' is defined in multiple extensions for 'TargetKind' and neither is more specific.
   - 'TargetKind' is from 'package:meta/meta_meta.dart' ('../../Developer/flutter/.pub-cache/hosted/pub.dartlang.org/meta-1.7.0/lib/meta_meta.dart').
  Try using an explicit extension application of the wanted extension or hiding unwanted extensions from scope.
          var kindNames = kinds.map((kind) =&gt; kind.displayString).toList()
                                                   ^^^^^^^^^^^^^
  ../../Developer/flutter/.pub-cache/hosted/pub.dartlang.org/analyzer-0.41.2/lib/src/error/best_practices_verifier.dart:1950:14: Context: This is one of the extension members.
    String get displayString {
               ^^^^^^^^^^^^^
  ../../Developer/flutter/.pub-cache/hosted/pub.dartlang.org/meta-1.7.0/lib/meta_meta.dart:91:14: Context: This is one of the extension members.
    String get displayString {
               ^^^^^^^^^^^^^
  ../../Developer/flutter/.pub-cache/hosted/pub.dartlang.org/analyzer-0.41.2/lib/src/error/best_practices_verifier.dart:260:36: Error: The getter 'commaSeparatedWithOr' isn't defined for the class 'List&lt;dynamic&gt;'.
   - 'List' is from 'dart:core'.
  Try correcting the name to the name of an existing getter, or defining a getter or field named 'commaSeparatedWithOr'.
          var validKinds = kindNames.commaSeparatedWithOr;
                                     ^^^^^^^^^^^^^^^^^^^^
  pub finished with exit code 1
  </code></pre>