json_annotation: put the wrapper helpers in their own file

json_annotation/lib/json_annotation.dart

@@ -11,3 +11,4 @@ library json_annotation;
 
 export 'src/json_literal.dart';
 export 'src/json_serializable.dart';
+export 'src/wrapper_helpers.dart';

json_annotation/lib/src/json_serializable.dart

@@ -2,8 +2,6 @@
 // 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:collection';
-
 /// An annotation used to specify a class to generate code for.
 class JsonSerializable {
   // TODO(kevmoo): document these fields
@@ -106,74 +104,3 @@ class JsonKey {
       this.fromJson,
       this.toJson});
 }
-
-/// Helper classes used in generated code when
-/// `JsonSerializableGenerator.useWrappers` is `true`.
-///
-/// Should not be used directly.
-abstract class $JsonMapWrapper extends UnmodifiableMapBase<String, dynamic> {}
-
-/// Helper function used in generated code when
-/// `JsonSerializableGenerator.useWrappers` is `true`.
-///
-/// Should not be used directly.
-Map<String, dynamic> $wrapMap<K, V>(
-        Map<K, V> source, dynamic converter(V key)) =>
-    new _MappingMap(source, converter);
-
-/// Helper function used in generated code when
-/// `JsonSerializableGenerator.useWrappers` is `true`.
-///
-/// Should not be used directly.
-Map<String, dynamic> $wrapMapHandleNull<K, V>(
-        Map<K, V> source, dynamic converter(V key)) =>
-    source == null ? null : new _MappingMap(source, converter);
-
-/// Helper function used in generated code when
-/// `JsonSerializableGenerator.useWrappers` is `true`.
-///
-/// Should not be used directly.
-List<dynamic> $wrapList<T>(List<T> source, dynamic converter(T key)) =>
-    new _MappingList(source, converter);
-
-/// Helper function used in generated code when
-/// `JsonSerializableGenerator.useWrappers` is `true`.
-///
-/// Should not be used directly.
-List<dynamic> $wrapListHandleNull<T>(
-        List<T> source, dynamic converter(T key)) =>
-    source == null ? null : new _MappingList(source, converter);
-
-typedef dynamic _Convert<S>(S value);
-
-class _MappingList<S> extends ListBase<dynamic> {
-  final List<S> _source;
-  final _Convert<S> _converter;
-
-  _MappingList(this._source, this._converter);
-
-  @override
-  dynamic operator [](int index) => _converter(_source[index]);
-
-  @override
-  operator []=(int index, dynamic value) => throw new UnsupportedError('');
-
-  @override
-  int get length => _source.length;
-
-  @override
-  set length(int value) => throw new UnsupportedError('');
-}
-
-class _MappingMap<K, V> extends UnmodifiableMapBase<String, dynamic> {
-  final Map<K, V> _source;
-  final _Convert<V> _converter;
-
-  _MappingMap(this._source, this._converter);
-
-  @override
-  Iterable<String> get keys => _source.keys.map((k) => k as String);
-
-  @override
-  dynamic operator [](Object key) => _converter(_source[key]);
-}

json_annotation/lib/src/wrapper_helpers.dart

@@ -0,0 +1,76 @@
+// Copyright (c) 2018, 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:collection';
+
+/// Helper classes used in generated code when
+/// `JsonSerializableGenerator.useWrappers` is `true`.
+///
+/// Should not be used directly.
+abstract class $JsonMapWrapper extends UnmodifiableMapBase<String, dynamic> {}
+
+/// Helper function used in generated code when
+/// `JsonSerializableGenerator.useWrappers` is `true`.
+///
+/// Should not be used directly.
+Map<String, dynamic> $wrapMap<K, V>(
+        Map<K, V> source, dynamic converter(V key)) =>
+    new _MappingMap(source, converter);
+
+/// Helper function used in generated code when
+/// `JsonSerializableGenerator.useWrappers` is `true`.
+///
+/// Should not be used directly.
+Map<String, dynamic> $wrapMapHandleNull<K, V>(
+        Map<K, V> source, dynamic converter(V key)) =>
+    source == null ? null : new _MappingMap(source, converter);
+
+/// Helper function used in generated code when
+/// `JsonSerializableGenerator.useWrappers` is `true`.
+///
+/// Should not be used directly.
+List<dynamic> $wrapList<T>(List<T> source, dynamic converter(T key)) =>
+    new _MappingList(source, converter);
+
+/// Helper function used in generated code when
+/// `JsonSerializableGenerator.useWrappers` is `true`.
+///
+/// Should not be used directly.
+List<dynamic> $wrapListHandleNull<T>(
+        List<T> source, dynamic converter(T key)) =>
+    source == null ? null : new _MappingList(source, converter);
+
+typedef dynamic _Convert<S>(S value);
+
+class _MappingList<S> extends ListBase<dynamic> {
+  final List<S> _source;
+  final _Convert<S> _converter;
+
+  _MappingList(this._source, this._converter);
+
+  @override
+  dynamic operator [](int index) => _converter(_source[index]);
+
+  @override
+  operator []=(int index, dynamic value) => throw new UnsupportedError('');
+
+  @override
+  int get length => _source.length;
+
+  @override
+  set length(int value) => throw new UnsupportedError('');
+}
+
+class _MappingMap<K, V> extends UnmodifiableMapBase<String, dynamic> {
+  final Map<K, V> _source;
+  final _Convert<V> _converter;
+
+  _MappingMap(this._source, this._converter);
+
+  @override
+  Iterable<String> get keys => _source.keys.map((k) => k as String);
+
+  @override
+  dynamic operator [](Object key) => _converter(_source[key]);
+}

json_annotation/pubspec.yaml

@@ -1,5 +1,5 @@
 name: json_annotation
-version: 0.2.4
+version: 0.2.5-dev
 description: Annotations for the json_serializable package
 homepage: https://github.com/dart-lang/json_serializable
 author: Dart Team <misc@dartlang.org>