Add static type checking of "yield" statements to analyzer.

pkg/analyzer/lib/src/generated/error.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 engine.error;
 
 import 'dart:collection';
 
 import 'ast.dart' show AstNode;
 import 'element.dart';
@@ skipping 3698 matching lines @@
    * @param argumentCount the number of type arguments provided
    * See [CompileTimeErrorCode.CONST_WITH_INVALID_TYPE_PARAMETERS], and
    * [CompileTimeErrorCode.NEW_WITH_INVALID_TYPE_PARAMETERS].
    */
   static const StaticTypeWarningCode WRONG_NUMBER_OF_TYPE_ARGUMENTS =
       const StaticTypeWarningCode(
           'WRONG_NUMBER_OF_TYPE_ARGUMENTS',
           "The type '{0}' is declared with {1} type parameters, but {2} type arguments were given");
 
   /**
+   * 17.16.1 Yield: Let T be the static type of e [the expression to the right
+   * of "yield"] and let f be the immediately enclosing function.  It is a
+   * static type warning if either:
+   *
+   * - the body of f is marked async* and the type Stream<T> may not be
+   *   assigned to the declared return type of f.
+   *
+   * - the body of f is marked sync* and the type Iterable<T> may not be
+   *   assigned to the declared return type of f.
+   */
+  static const StaticTypeWarningCode YIELD_OF_INVALID_TYPE =
+      const StaticTypeWarningCode(
+          'YIELD_OF_INVALID_TYPE',
+          "The declared return type '{0}' is incompatible with the type '{1}' implied by the 'yield' expression");
+
+  /**
    * Initialize a newly created error code to have the given [name]. The message
    * associated with the error will be created from the given [message]
    * template. The correction associated with the error will be created from the
    * given [correction] template.
    */
   const StaticTypeWarningCode(String name, String message, [String correction])
       : super(name, message, correction);
 
   @override
   ErrorSeverity get errorSeverity => ErrorType.STATIC_TYPE_WARNING.severity;
@@ skipping 1249 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;
 }