Issue 27515. Report DUPLICATE_PAR when the same library contains two part directives with the same …

pkg/analyzer/lib/src/error/codes.dart

 // Copyright (c) 2014, 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.
 
 library analyzer.src.error.codes;
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 
 /**
@@ skipping 734 matching lines @@
    * a static member with the same name.
    *
    * Parameters:
    * 0: the name of the duplicate entity
    */
   static const CompileTimeErrorCode DUPLICATE_DEFINITION =
       const CompileTimeErrorCode(
           'DUPLICATE_DEFINITION', "The name '{0}' is already defined");
 
   /**
+   * 18.3 Parts: It's a compile-time error if the same library contains two part
+   * directives with the same URI.
+   *
+   * Parameters:
+   * 0: the URI of the duplicate part
+   */
+  static const CompileTimeErrorCode DUPLICATE_PART = const CompileTimeErrorCode(
+      'DUPLICATE_PART',
+      "The library already contains a part with the uri '{0}'.");
+
+  /**
    * 7. Classes: It is a compile-time error if a class has an instance member
    * and a static member with the same name.
    *
    * This covers the additional duplicate definition cases where inheritance has
    * to be considered.
    *
    * Parameters:
    * 0: the name of the class that has conflicting instance/static members
    * 1: the name of the conflicting members
    *
@@ skipping 4100 matching lines @@
    * Initialize a newly created error code to have the given [name].
    */
   const TodoCode(String name) : super(name, "{0}");
 
   @override
   ErrorSeverity get errorSeverity => ErrorSeverity.INFO;
 
   @override
   ErrorType get type => ErrorType.TODO;
 }