element support for @reopen

See: https://github.com/dart-lang/linter/issues/3917

Change-Id: I9652fabcbac37644cfca89227b6830e32a79576d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/279657
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Phil Quitslund <pquitslund@google.com>

pkg/analyzer/lib/dart/element/element.dart

@@ -592,6 +592,9 @@ abstract class Element implements AnalysisTarget {
   /// Return `true` if this element has an annotation of the form `@protected`.
   bool get hasProtected;
 
+  /// Return `true` if this element has an annotation of the form `@reopen`.
+  bool get hasReopen;
+
   /// Return `true` if this element has an annotation of the form `@required`.
   bool get hasRequired;
 
@@ -831,6 +834,10 @@ abstract class ElementAnnotation implements ConstantEvaluationTarget {
   /// implementing a proxy object.
   bool get isProxy;
 
+  /// Return `true` if this annotation marks the associated member as being
+  /// reopened.
+  bool get isReopen;
+
   /// Return `true` if this annotation marks the associated member as being
   /// required.
   bool get isRequired;

pkg/analyzer/lib/src/dart/element/element.dart

@@ -1983,6 +1983,10 @@ class ElementAnnotationImpl implements ElementAnnotation {
   /// protected.
   static const String _protectedVariableName = 'protected';
 
+  /// The name of the top-level variable used to mark a class or mixin as being
+  /// reopened.
+  static const String _reopenVariableName = 'reopen';
+
   /// The name of the class used to mark a parameter as being required.
   static const String _requiredClassName = 'Required';
 
@@ -2119,6 +2123,9 @@ class ElementAnnotationImpl implements ElementAnnotation {
   @override
   bool get isProxy => false;
 
+  @override
+  bool get isReopen => _isPackageMetaGetter(_reopenVariableName);
+
   @override
   bool get isRequired =>
       _isConstructor(
@@ -2503,6 +2510,18 @@ abstract class ElementImpl implements Element {
     return false;
   }
 
+  @override
+  bool get hasReopen {
+    final metadata = this.metadata;
+    for (var i = 0; i < metadata.length; i++) {
+      var annotation = metadata[i];
+      if (annotation.isReopen) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   @override
   bool get hasRequired {
     final metadata = this.metadata;
@@ -5090,6 +5109,9 @@ class MultiplyDefinedElementImpl implements MultiplyDefinedElement {
   @override
   bool get hasProtected => false;
 
+  @override
+  bool get hasReopen => false;
+
   @override
   bool get hasRequired => false;
 

pkg/analyzer/lib/src/dart/element/member.dart

@@ -569,6 +569,9 @@ abstract class Member implements Element {
   @override
   bool get hasProtected => _declaration.hasProtected;
 
+  @override
+  bool get hasReopen => _declaration.hasReopen;
+
   @override
   bool get hasRequired => _declaration.hasRequired;
 

pkg/analyzer/lib/src/test_utilities/mock_packages.dart

@@ -84,6 +84,8 @@ const _OptionalTypeArgs optionalTypeArgs = _OptionalTypeArgs();
 
 const _Protected protected = _Protected();
 
+const _Reopen reopen = _Reopen();
+
 const Required required = Required();
 
 const _Sealed sealed = _Sealed();
@@ -103,6 +105,14 @@ class Immutable {
   const Immutable([this.reason = '']);
 }
 
+@Target({
+  TargetKind.classType,
+  TargetKind.mixinType,
+})
+class _Reopen {
+  const _Reopen();
+}
+
 class Required {
   final String reason;