Export GeneratedMessageGenericExtensions in generated files

Currently when a user calls deprecated methods `clone` or `copyWith`,
the deprecation message points to `GeneratedMessageGenericExtensions`
`deepCopy` and `rebuild` methods.

However we can't just replace `clone` with `deepCopy` as currently the
extension is not exported by the generated files. Instead we need to
import the library explicitly in the use site.

We could mention this in the deprecation message ("Use rebuild from
protobuf library instead"), but it's more convenient to just export the
extension in the generated message files.

protoc_plugin/CHANGELOG.md

@@ -5,9 +5,13 @@
   fields is now `PbMap` (instead of `Map`). ([#903])
 
   This change requires protobuf-4.0.0.
+* Generated files now export `GeneratedMessageGenericExtensions` from the
+  protobuf library. ([#503], [#907])
 
 [#738]: https://github.com/google/protobuf.dart/issues/738
 [#903]: https://github.com/google/protobuf.dart/pull/903
+[#503]: https://github.com/google/protobuf.dart/issues/503
+[#907]: https://github.com/google/protobuf.dart/pull/907
 
 ## 21.1.2
 

protoc_plugin/lib/indenting_writer.dart

@@ -173,14 +173,16 @@ class ImportWriter {
   final Set<String> _dartImports = SplayTreeSet<String>();
   final Set<String> _packageImports = SplayTreeSet<String>();
   final Set<String> _fileImports = SplayTreeSet<String>();
-  final Set<String> _exports = SplayTreeSet<String>();
+  final Set<String> _packageExports = SplayTreeSet<String>();
+  final Set<String> _fileExports = SplayTreeSet<String>();
 
   /// Whether any imports were written.
   bool get hasImports =>
       _dartImports.isNotEmpty ||
       _packageImports.isNotEmpty ||
       _fileImports.isNotEmpty ||
-      _exports.isNotEmpty;
+      _packageExports.isNotEmpty ||
+      _fileExports.isNotEmpty;
 
   /// Add an import with an optional import prefix.
   void addImport(String url, {String? prefix}) {
@@ -196,8 +198,15 @@ class ImportWriter {
   }
 
   /// And an export.
-  void addExport(String url) {
-    _exports.add("export '$url';");
+  void addExport(String url, {List<String> members = const []}) {
+    final directive = members.isNotEmpty
+        ? "export '$url' show ${members.join(', ')};"
+        : "export '$url';";
+    if (url.startsWith('package:')) {
+      _packageExports.add(directive);
+    } else {
+      _fileExports.add(directive);
+    }
   }
 
   /// Return the generated text for the set of imports.
@@ -215,9 +224,13 @@ class ImportWriter {
       if (buf.isNotEmpty) buf.writeln();
       _fileImports.forEach(buf.writeln);
     }
-    if (_exports.isNotEmpty) {
+    if (_packageExports.isNotEmpty) {
+      if (buf.isNotEmpty) buf.writeln();
+      _packageExports.forEach(buf.writeln);
+    }
+    if (_fileExports.isNotEmpty) {
       if (buf.isNotEmpty) buf.writeln();
-      _exports.forEach(buf.writeln);
+      _fileExports.forEach(buf.writeln);
     }
 
     return buf.toString();

protoc_plugin/lib/src/file_generator.dart

@@ -341,6 +341,9 @@ class FileGenerator extends ProtobufContainer {
       _addImport(importWriter, config, target, '.pbenum.dart');
     }
 
+    importWriter.addExport(_protobufImportUrl,
+        members: ['GeneratedMessageGenericExtensions']);
+
     for (final publicDependency in descriptor.publicDependency) {
       _addExport(importWriter, config,
           Uri.file(descriptor.dependency[publicDependency]), '.pb.dart');

protoc_plugin/test/goldens/grpc_service.pb

@@ -13,6 +13,8 @@ import 'dart:core' as $core;
 
 import 'package:protobuf/protobuf.dart' as $pb;
 
+export 'package:protobuf/protobuf.dart' show GeneratedMessageGenericExtensions;
+
 class Empty extends $pb.GeneratedMessage {
   factory Empty() => create();
   Empty._() : super();

protoc_plugin/test/goldens/header_in_package.pb

@@ -13,3 +13,5 @@ import 'dart:core' as $core;
 
 import 'package:protobuf/protobuf.dart' as $pb;
 
+export 'package:protobuf/protobuf.dart' show GeneratedMessageGenericExtensions;
+

protoc_plugin/test/goldens/header_with_fixnum.pb

@@ -14,3 +14,5 @@ import 'dart:core' as $core;
 import 'package:fixnum/fixnum.dart' as $fixnum;
 import 'package:protobuf/protobuf.dart' as $pb;
 
+export 'package:protobuf/protobuf.dart' show GeneratedMessageGenericExtensions;
+

protoc_plugin/test/goldens/imports.pb

@@ -16,6 +16,8 @@ import 'package:protobuf/protobuf.dart' as $pb;
 import 'package1.pb.dart' as $1;
 import 'package2.pb.dart' as $2;
 
+export 'package:protobuf/protobuf.dart' show GeneratedMessageGenericExtensions;
+
 class M extends $pb.GeneratedMessage {
   factory M() => create();
   M._() : super();

protoc_plugin/test/goldens/int64.pb

@@ -14,6 +14,8 @@ import 'dart:core' as $core;
 import 'package:fixnum/fixnum.dart' as $fixnum;
 import 'package:protobuf/protobuf.dart' as $pb;
 
+export 'package:protobuf/protobuf.dart' show GeneratedMessageGenericExtensions;
+
 class Int64 extends $pb.GeneratedMessage {
   factory Int64() => create();
   Int64._() : super();

protoc_plugin/test/goldens/oneMessage.pb

@@ -13,6 +13,8 @@ import 'dart:core' as $core;
 
 import 'package:protobuf/protobuf.dart' as $pb;
 
+export 'package:protobuf/protobuf.dart' show GeneratedMessageGenericExtensions;
+
 class PhoneNumber extends $pb.GeneratedMessage {
   factory PhoneNumber() => create();
   PhoneNumber._() : super();

protoc_plugin/test/goldens/oneMessage.pb.meta

@@ -2,121 +2,121 @@ annotation: {
   path: 4
   path: 0
   sourceFile: test
-  begin: 445
-  end: 456
+  begin: 526
+  end: 537
 }
 annotation: {
   path: 4
   path: 0
   sourceFile: test
-  begin: 527
-  end: 538
+  begin: 608
+  end: 619
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 0
   sourceFile: test
-  begin: 2247
-  end: 2253
+  begin: 2328
+  end: 2334
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 0
   sourceFile: test
-  begin: 2295
-  end: 2301
+  begin: 2376
+  end: 2382
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 0
   sourceFile: test
-  begin: 2374
-  end: 2383
+  begin: 2455
+  end: 2464
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 0
   sourceFile: test
-  begin: 2426
-  end: 2437
+  begin: 2507
+  end: 2518
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 1
   sourceFile: test
-  begin: 2495
-  end: 2499
+  begin: 2576
+  end: 2580
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 1
   sourceFile: test
-  begin: 2541
-  end: 2545
+  begin: 2622
+  end: 2626
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 1
   sourceFile: test
-  begin: 2620
-  end: 2627
+  begin: 2701
+  end: 2708
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 1
   sourceFile: test
-  begin: 2670
-  end: 2679
+  begin: 2751
+  end: 2760
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 2
   sourceFile: test
-  begin: 2740
-  end: 2744
+  begin: 2821
+  end: 2825
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 2
   sourceFile: test
-  begin: 2791
-  end: 2795
+  begin: 2872
+  end: 2876
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 2
   sourceFile: test
-  begin: 2868
-  end: 2875
+  begin: 2949
+  end: 2956
 }
 annotation: {
   path: 4
   path: 0
   path: 2
   path: 2
   sourceFile: test
-  begin: 2918
-  end: 2927
+  begin: 2999
+  end: 3008
 }

protoc_plugin/test/goldens/service.pb

@@ -14,6 +14,8 @@ import 'dart:core' as $core;
 
 import 'package:protobuf/protobuf.dart' as $pb;
 
+export 'package:protobuf/protobuf.dart' show GeneratedMessageGenericExtensions;
+
 class Empty extends $pb.GeneratedMessage {
   factory Empty() => create();
   Empty._() : super();

protoc_plugin/test/goldens/topLevelEnum.pb

@@ -11,5 +11,7 @@
 
 import 'dart:core' as $core;
 
+export 'package:protobuf/protobuf.dart' show GeneratedMessageGenericExtensions;
+
 export 'test.pbenum.dart';
 

protoc_plugin/test/oneof_test.dart

@@ -2,7 +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 'package:protobuf/protobuf.dart';
 import 'package:test/test.dart';
 
 import '../out/protos/oneof.pb.dart';