Add support for patching parts.

pkg/analyzer/test/src/dart/sdk/patch_test.dart

 // Copyright (c) 2016, 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 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/src/dart/sdk/patch.dart';
 import 'package:analyzer/src/dart/sdk/sdk.dart';
@@ skipping 372 matching lines @@
     patches: {VM_PLATFORM: ['does_not_exists.dart']}),
 };''');
       _createSdk();
       File file = provider.newFile(_p('/sdk/lib/test/test.dart'), '');
       Source source = file.createSource(FastUri.parse('dart:test'));
       CompilationUnit unit = SdkPatcher.parse(source, true, listener);
       patcher.patch(sdk, SdkLibraryImpl.VM_PLATFORM, listener, source, unit);
     }, throwsArgumentError);
   }
 
+  test_part() {
+    String baseLibCode = r'''
+library test;
+part 'test_part.dart';
+class A {}
+''';
+    String basePartCode = r'''
+part of test;
+class B {}
+''';
+    _setSdkLibraries(r'''
+final Map<String, LibraryInfo> LIBRARIES = const <String, LibraryInfo> {
+  'test' : const LibraryInfo(
+    'test/test.dart',
+    patches: {VM_PLATFORM: ['test/test_patch.dart']}),
+};''');
+    File fileLib = provider.newFile(_p('/sdk/lib/test/test.dart'), baseLibCode);
+    File filePart =
+        provider.newFile(_p('/sdk/lib/test/test_part.dart'), basePartCode);
+    provider.newFile(
+        _p('/sdk/lib/test/test_patch.dart'),
+        r'''
+import 'foo.dart';
+
+@patch
+class A {
+  int _a() => 1;
+}
+
+@patch
+class B {
+  int _b() => 1;
+}
+
+class _C {}
+''');
+
+    _createSdk();
+
+    {
+      Uri uri = FastUri.parse('dart:test');
+      Source source = fileLib.createSource(uri);
+      CompilationUnit unit = SdkPatcher.parse(source, true, listener);
+      patcher.patch(sdk, SdkLibraryImpl.VM_PLATFORM, listener, source, unit);
+      _assertUnitCode(
+          unit,
+          "library test; part 'test_part.dart'; import 'foo.dart'; "
+          "class A {int _a() => 1;} class _C {}");
+    }
+
+    {
+      Uri uri = FastUri.parse('dart:test/test_part.dart');
+      Source source = filePart.createSource(uri);
+      CompilationUnit unit = SdkPatcher.parse(source, true, listener);
+      patcher.patch(sdk, SdkLibraryImpl.VM_PLATFORM, listener, source, unit);
+      _assertUnitCode(unit, "part of test; class B {int _b() => 1;}");
+    }
+  }
+
   test_topLevel_class_append() {
     CompilationUnit unit = _doTopLevelPatching(
         r'''
 class A {}
 ''',
         r'''
 class _B {
   void mmm() {}
 }
 ''');
@@ skipping 235 matching lines @@
   void _setSdkLibraries(String code) {
     provider.newFile(
         _p('/sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart'), code);
   }
 
   static void _assertPrevNextToken(Token prev, Token next) {
     expect(prev.next, same(next));
     expect(next.previous, same(prev));
   }
 }