[wildcards] update UNUSED_ELEMENT reporting for local functions

Change-Id: Id15e72ae91ee46273a80bec7af447e5a0fa41cca
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/368880
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

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

@@ -756,8 +756,11 @@ class UnusedLocalElementsVerifier extends RecursiveAstVisitor<void> {
   }
 
   /// Returns whether the name of [element] should be treated as a wildcard.
-  bool _isNamedWildcard(LocalVariableElement element) {
-    String name = element.name;
+  bool _isNamedWildcard(LocalElement element) {
+    // TODO(pq): ask the element once implemented.
+    var name = element.name;
+    if (name == null) return false;
+
     var length = name.length;
     if (length > 1 && _wildCardVariablesEnabled) return false;
 
@@ -1013,6 +1016,10 @@ class UnusedLocalElementsVerifier extends RecursiveAstVisitor<void> {
 
   void _visitFunctionElement(FunctionElement element) {
     if (!_isUsedElement(element)) {
+      if (_wildCardVariablesEnabled) {
+        if (element.isLocal && _isNamedWildcard(element)) return;
+      }
+
       _reportErrorForElement(
           WarningCode.UNUSED_ELEMENT, element, [element.displayName]);
     }
@@ -1156,3 +1163,8 @@ class UsedLocalElements {
     return catchStackTraceElements.contains(element);
   }
 }
+
+extension on FunctionElement {
+  bool get isLocal =>
+      enclosingElement is FunctionElement || enclosingElement is MethodElement;
+}

pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart

@@ -633,3 +633,10 @@ mixin WithStrictCastsMixin on PubPackageResolutionTest {
   Future<void> assertNoErrorsWithStrictCasts(String code) async =>
       assertErrorsWithStrictCasts(code, []);
 }
+
+// TODO(pq): revisit, https://dart-review.googlesource.com/c/sdk/+/368880
+mixin WithWildCardVariablesMixin on PubPackageResolutionTest {
+  @override
+  List<String> get experiments =>
+      [...super.experiments, Feature.wildcard_variables.enableString];
+}

pkg/analyzer/test/src/diagnostics/unused_element_test.dart

@@ -2,8 +2,7 @@
 // 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.
 
-import 'package:analyzer/src/dart/error/hint_codes.dart';
-import 'package:analyzer/src/error/codes.g.dart';
+import 'package:analyzer/src/error/codes.dart';
 import 'package:test/expect.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ -12,6 +11,7 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(UnusedElementTest);
+    defineReflectiveTests(UnusedElementWildCardVariablesTest);
   });
 }
 
@@ -571,6 +571,22 @@ class A {
 ''');
   }
 
+  test_function_underscore() async {
+    await assertErrorsInCode(r'''
+_(){}
+''', [
+      error(WarningCode.UNUSED_ELEMENT, 0, 1),
+    ]);
+  }
+
+  test_function_underscores() async {
+    await assertErrorsInCode(r'''
+__(){}
+''', [
+      error(WarningCode.UNUSED_ELEMENT, 0, 2),
+    ]);
+  }
+
   test_functionLocal_isUsed_closure() async {
     await assertNoErrorsInCode(r'''
 main() {
@@ -824,6 +840,50 @@ class A {
     ]);
   }
 
+  test_localFunction_inFunction_wildcard() async {
+    await assertErrorsInCode(r'''
+main() {
+  _(){}
+}
+''', [
+      error(WarningCode.UNUSED_ELEMENT, 11, 1),
+    ]);
+  }
+
+  test_localFunction_inMethod_underscores() async {
+    await assertErrorsInCode(r'''
+class C {
+  m() {
+    __(){}
+  }
+}
+''', [
+      error(WarningCode.UNUSED_ELEMENT, 22, 2),
+    ]);
+  }
+
+  test_localFunction_inMethod_wildcard() async {
+    await assertErrorsInCode(r'''
+class C {
+  m() {
+    _(){}
+  }
+}
+''', [
+      error(WarningCode.UNUSED_ELEMENT, 22, 1),
+    ]);
+  }
+
+  test_localFunction_underscores() async {
+    await assertErrorsInCode(r'''
+main() {
+  __(){}
+}
+''', [
+      error(WarningCode.UNUSED_ELEMENT, 11, 2),
+    ]);
+  }
+
   test_method_isUsed_hasPragma_vmEntryPoint() async {
     pragma;
     await assertNoErrorsInCode(r'''
@@ -2863,3 +2923,27 @@ typedef _A = List<int>;
     ]);
   }
 }
+
+@reflectiveTest
+class UnusedElementWildCardVariablesTest extends UnusedElementTest
+    with WithWildCardVariablesMixin {
+  @override
+  test_localFunction_inFunction_wildcard() async {
+    await assertNoErrorsInCode(r'''
+m() {
+  _(){}
+}
+''');
+  }
+
+  @override
+  test_localFunction_inMethod_wildcard() async {
+    await assertNoErrorsInCode(r'''
+class C {
+  m() {
+    _(){}
+  }
+}
+''');
+  }
+}