analyzer: Count unused local functions in Element2.isWildcardVariable

I think this was just overlooked. While prefixes and local functions
are not variables by any stretch, the feature name is "wildcard
variables" so there you have it.

This change allows us to remove some stale code in linter.

Change-Id: I1fffe0a53042d3ba20208463b3587e8ad78a9424
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/416880
Commit-Queue: Samuel Rawlins <[email protected]>
Reviewed-by: Phil Quitslund <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>

Author: srawlins

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

@@ -79,7 +79,8 @@ extension Element2Extension on Element2 {
   /// Whether this element is a wildcard variable.
   bool get isWildcardVariable {
     return name3 == '_' &&
-        (this is LocalVariableElement2 ||
+        (this is LocalFunctionElement ||
+            this is LocalVariableElement2 ||
             this is PrefixElement2 ||
             this is TypeParameterElement2 ||
             (this is FormalParameterElement &&

pkg/analyzer/lib/src/error/unused_local_elements_verifier.dart

@@ -15,6 +15,7 @@ import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/ast/extensions.dart';
 import 'package:analyzer/src/dart/element/element.dart'
     show JoinPatternVariableElementImpl2, MetadataImpl;
+import 'package:analyzer/src/dart/element/extensions.dart';
 import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
 import 'package:analyzer/src/dart/element/member.dart' show ExecutableMember;
 import 'package:analyzer/src/dart/element/type.dart';
@@ -783,21 +784,13 @@ class UnusedLocalElementsVerifier extends RecursiveAstVisitor<void> {
 
   /// Returns whether the name of [element] should be treated as a wildcard.
   bool _isNamedWildcard(LocalElement2 element) {
-    // TODO(pq): ask the element once implemented.
-    var name = element.name3;
-    if (name == null) return false;
-
-    var length = name.length;
-    if (length > 1 && _wildCardVariablesEnabled) return false;
-
-    for (int index = length - 1; index >= 0; --index) {
-      if (name.codeUnitAt(index) != 0x5F) {
-        // 0x5F => '_'
-        return false;
-      }
+    if (_wildCardVariablesEnabled) {
+      return element.isWildcardVariable;
+    } else {
+      var name = element.name3;
+      if (name == null) return false;
+      return name.codeUnits.every((e) => e == 0x5F /* '_' */);
     }
-
-    return true;
   }
 
   bool _isPrivateClassOrExtension(Element2 element) =>