Validation of `@required` params (#26182).

pkg/analyzer/lib/dart/element/element.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.
 
 /**
  * Defines the element model. The element model describes the semantic (as
  * opposed to syntactic) structure of Dart code. The syntactic structure of the
  * code is modeled by the [AST structure](../ast/ast.dart).
  *
  * The element model consists of two closely related kinds of objects: elements
@@ skipping 628 matching lines @@
    */
   bool get isProtected;
 
   /**
    * Return `true` if this element is public. Public elements are visible within
    * any library that imports the library in which they are declared.
    */
   bool get isPublic;
 
   /**
+   * Return `true` if this element has an annotation of the form '@required'.
+   */
+  bool get isRequired;
+
+  /**
    * Return `true` if this element is synthetic. A synthetic element is an
    * element that is not represented in the source code explicitly, but is
    * implied by the source code, such as the default constructor for a class
    * that does not explicitly define any constructors.
    */
   bool get isSynthetic;
 
   /**
    * Return the kind of element that this is.
    */
@@ skipping 164 matching lines @@
    * Return `true` if this annotation marks the associated member as being
    * protected.
    */
   bool get isProtected;
 
   /**
    * Return `true` if this annotation marks the associated class as implementing
    * a proxy object.
    */
   bool get isProxy;
+
+  /**
+   * Return `true` if this annotation marks the associated member as being
+   * required.
+   */
+  bool get isRequired;
 }
 
 /**
  * The enumeration `ElementKind` defines the various kinds of elements in the
  * element model.
  *
  * Clients may not extend, implement or mix-in this class.
  */
 class ElementKind extends Enum<ElementKind> {
   static const ElementKind CLASS = const ElementKind('CLASS', 0, "class");
@@ skipping 1125 matching lines @@
    */
   bool get isStatic;
 
   /**
    * Return the declared type of this variable, or `null` if the variable did
    * not have a declared type (such as if it was declared using the keyword
    * 'var').
    */
   DartType get type;
 }