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

pkg/analyzer/lib/src/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.
 
 library analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1631 matching lines @@
    */
   static String _PROTECTED_VARIABLE_NAME = "protected";
 
   /**
    * The name of the top-level variable used to mark a class as implementing a
    * proxy object.
    */
   static String PROXY_VARIABLE_NAME = "proxy";
 
   /**
+   * The name of the class used to mark a parameter as being required.
+   */
+  static String _REQUIRED_CLASS_NAME = "Required";
+
+  /**
+   * The name of the top-level variable used to mark a parameter as being
+   * required.
+   */
+  static String _REQUIRED_VARIABLE_NAME = "required";
+
+  /**
    * The element representing the field, variable, or constructor being used as
    * an annotation.
    */
   Element element;
 
   /**
    * The compilation unit in which this annotation appears.
    */
   final CompilationUnitElementImpl compilationUnit;
 
@@ skipping 51 matching lines @@
       element is PropertyAccessorElement &&
       element.name == _PROTECTED_VARIABLE_NAME &&
       element.library?.name == _META_LIB_NAME;
 
   @override
   bool get isProxy =>
       element is PropertyAccessorElement &&
       element.name == PROXY_VARIABLE_NAME &&
       element.library?.isDartCore == true;
 
+  @override
+  bool get isRequired =>
+      element is ConstructorElement &&
+          element.enclosingElement.name == _REQUIRED_CLASS_NAME &&
+          element.library?.name == _META_LIB_NAME ||
+      element is PropertyAccessorElement &&
+          element.name == _REQUIRED_VARIABLE_NAME &&
+          element.library?.name == _META_LIB_NAME;
+
   /**
    * Get the library containing this annotation.
    */
   Source get librarySource => compilationUnit.librarySource;
 
   @override
   Source get source => compilationUnit.source;
 
   @override
   String toString() => '@$element';
@@ skipping 195 matching lines @@
         return true;
       }
     }
     return false;
   }
 
   @override
   bool get isPublic => !isPrivate;
 
   @override
+  bool get isRequired {
+    for (ElementAnnotation annotation in metadata) {
+      if (annotation.isRequired) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  @override
   bool get isSynthetic => hasModifier(Modifier.SYNTHETIC);
 
   @override
   LibraryElement get library =>
       getAncestor((element) => element is LibraryElement);
 
   @override
   ElementLocation get location {
     if (_cachedLocation == null) {
       if (library == null) {
@@ skipping 2138 matching lines @@
     return Identifier.isPrivateName(name);
   }
 
   @override
   bool get isProtected => false;
 
   @override
   bool get isPublic => !isPrivate;
 
   @override
+  bool get isRequired => false;
+
+  @override
   bool get isSynthetic => true;
 
   @override
   ElementKind get kind => ElementKind.ERROR;
 
   @override
   LibraryElement get library => null;
 
   @override
   ElementLocation get location => null;
@@ skipping 859 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }