Update validation for final fields with const enum constructor.

For now just making it to not crash.

Change-Id: I415f0c7e17cc959f26f87acd2d662e7f6de3b39b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/229780
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

Author: scheglov

pkg/analyzer/lib/src/dart/ast/extensions.dart

@@ -76,6 +76,21 @@ DartType? _writeType(AstNode node) {
   return null;
 }
 
+extension AstNodeNullableExtension on AstNode? {
+  List<ClassMember> get classMembers {
+    final self = this;
+    if (self is ClassOrMixinDeclaration) {
+      return self.members;
+    } else if (self is EnumDeclaration) {
+      return self.members;
+    } else if (self is ExtensionDeclaration) {
+      return self.members;
+    } else {
+      throw UnimplementedError('(${self.runtimeType}) $self');
+    }
+  }
+}
+
 extension ConstructorDeclarationExtension on ConstructorDeclaration {
   bool get isNonRedirectingGenerative {
     // Must be generative.

pkg/analyzer/lib/src/dart/constant/constant_verifier.dart

@@ -103,8 +103,7 @@ class ConstantVerifier extends RecursiveAstVisitor<void> {
     if (constKeyword != null) {
       _validateConstructorInitializers(node);
       if (node.factoryKeyword == null) {
-        _validateFieldInitializers(
-            node.parent as ClassOrMixinDeclaration, constKeyword);
+        _validateFieldInitializers(node.parent.classMembers, constKeyword);
       }
     }
     _validateDefaultValues(node.parameters);
@@ -545,12 +544,11 @@ class ConstantVerifier extends RecursiveAstVisitor<void> {
   }
 
   /// Validates that the expressions of any field initializers in
-  /// [classDeclaration] are all compile-time constants. Since this is only
+  /// [members] are all compile-time constants. Since this is only
   /// required if the class has a constant constructor, the error is reported at
   /// [constKeyword], the const keyword on such a constant constructor.
   void _validateFieldInitializers(
-      ClassOrMixinDeclaration classDeclaration, Token constKeyword) {
-    NodeList<ClassMember> members = classDeclaration.members;
+      List<ClassMember> members, Token constKeyword) {
     for (ClassMember member in members) {
       if (member is FieldDeclaration && !member.isStatic) {
         for (VariableDeclaration variableDeclaration

pkg/analyzer/lib/src/generated/error_verifier.dart

@@ -202,11 +202,7 @@ class ErrorVerifier extends RecursiveAstVisitor<void>
 
   /// The class containing the AST nodes being visited, or `null` if we are not
   /// in the scope of a class.
-  ClassElementImpl? _enclosingClass;
-
-  /// The enum containing the AST nodes being visited, or `null` if we are not
-  /// in the scope of an enum.
-  ClassElement? _enclosingEnum;
+  ClassElement? _enclosingClass;
 
   /// The element of the extension being visited, or `null` if we are not
   /// in the scope of an extension.
@@ -281,11 +277,8 @@ class ErrorVerifier extends RecursiveAstVisitor<void>
   /// should not be modified in the middle of visiting a tree and requires an
   /// analyzer-provided Impl instance to work.
   set enclosingClass(ClassElement? classElement) {
-    assert(classElement is ClassElementImpl);
     assert(_enclosingClass == null);
-    assert(_enclosingEnum == null);
     assert(_enclosingExecutable.element == null);
-    _enclosingClass = classElement as ClassElementImpl;
   }
 
   /// The language team is thinking about adding abstract fields, or external
@@ -563,13 +556,13 @@ class ErrorVerifier extends RecursiveAstVisitor<void>
 
   @override
   void visitEnumDeclaration(EnumDeclaration node) {
-    var outerEnum = _enclosingEnum;
+    var outerClass = _enclosingClass;
     try {
-      _enclosingEnum = node.declaredElement;
+      _enclosingClass = node.declaredElement;
       _duplicateDefinitionVerifier.checkEnum(node);
       super.visitEnumDeclaration(node);
     } finally {
-      _enclosingEnum = outerEnum;
+      _enclosingClass = outerClass;
     }
   }
 
@@ -4408,9 +4401,6 @@ class ErrorVerifier extends RecursiveAstVisitor<void>
     if (identical(enclosingElement, _enclosingClass)) {
       return;
     }
-    if (identical(enclosingElement, _enclosingEnum)) {
-      return;
-    }
     if (enclosingElement is! ClassElement) {
       return;
     }