don't lint prefer_void_to_null on augmented fields/top-level vars

Fixes: https://github.com/dart-lang/linter/issues/4890

Change-Id: I9a44793e2e79ae946b5f010b9e588a6b8f29fc80
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/362065
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

pkg/linter/lib/src/extensions.dart

@@ -30,10 +30,12 @@ extension AstNodeExtension on AstNode {
     return switch (self) {
       ClassDeclaration() => self.augmentKeyword != null,
       ConstructorDeclaration() => self.augmentKeyword != null,
+      FieldDeclaration() => self.augmentKeyword != null,
       FunctionDeclarationImpl() => self.augmentKeyword != null,
       FunctionExpression() => self.parent?.isAugmentation ?? false,
       MethodDeclaration() => self.augmentKeyword != null,
       MixinDeclaration() => self.augmentKeyword != null,
+      TopLevelVariableDeclaration() => self.augmentKeyword != null,
       VariableDeclaration(declaredElement: var element) =>
         element is PropertyInducingElement && element.isAugmentation,
       _ => false

pkg/linter/lib/src/rules/prefer_void_to_null.dart

@@ -154,9 +154,11 @@ class _Visitor extends SimpleAstVisitor<void> {
     }
 
     if (parent != null) {
-      AstNode? member = parent.thisOrAncestorOfType<ClassMember>();
-      member ??= parent.thisOrAncestorOfType<NamedCompilationUnitMember>();
-      if (member?.isAugmentation ?? false) return;
+      AstNode? declaration = parent.thisOrAncestorOfType<ClassMember>();
+      declaration ??= parent.thisOrAncestorOfType<NamedCompilationUnitMember>();
+      declaration ??=
+          parent.thisOrAncestorOfType<TopLevelVariableDeclaration>();
+      if (declaration?.isAugmentation ?? false) return;
     }
 
     rule.reportLintForToken(node.name2);

pkg/linter/test/rules/prefer_void_to_null_test.dart

@@ -17,9 +17,6 @@ class PreferVoidToNullTest extends LintRuleTest {
   @override
   String get lintRule => 'prefer_void_to_null';
 
-  @FailingTest(
-      issue: 'https://github.com/dart-lang/linter/issues/4890',
-      reason: 'Null check operator used on a null value')
   test_augmentedField() async {
     newFile('$testPackageLibPath/a.dart', r'''
 import augment 'test.dart';
@@ -102,10 +99,6 @@ augment Future<Null>? get v => null;
 ''');
   }
 
-  @FailingTest(
-      issue: 'https://github.com/dart-lang/linter/issues/4890',
-      reason:
-          "CompileTimeErrorCode.DUPLICATE_DEFINITION [49, 1, The name 'v' is already defined.]")
   test_augmentedTopLevelVariable() async {
     newFile('$testPackageLibPath/a.dart', r'''
 import augment 'test.dart';