[wildcards] completion suggestion support

See: #56361

To follow, a bunch of tests to make sure `__`, `___`, etc are not incorrectly getting special cased.

Change-Id: I3d35a5344e09011460c074fdd43eccdac452a8ad
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/378623
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

pkg/analysis_server/lib/src/services/completion/dart/declaration_helper.dart

@@ -15,6 +15,7 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/ast/extensions.dart';
 import 'package:analyzer/src/dart/element/element.dart';
+import 'package:analyzer/src/dart/element/extensions.dart';
 import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/dart/element/type_algebra.dart';
 import 'package:analyzer/src/dart/resolver/applicable_extensions.dart';
@@ -318,6 +319,10 @@ class DeclarationHelper {
         continue;
       }
 
+      if (prefixElement.isWildcardVariable) {
+        continue;
+      }
+
       var importedLibrary = element.importedLibrary;
       if (importedLibrary == null) {
         continue;
@@ -661,6 +666,9 @@ class DeclarationHelper {
     required Namespace namespace,
     required String? prefix,
   }) {
+    // Don't suggest declarations in wildcard prefixed namespaces.
+    if (prefix == '_') return;
+
     var importData = ImportData(
       libraryUri: library.source.uri,
       prefix: prefix,
@@ -1622,6 +1630,8 @@ class DeclarationHelper {
           (mustBeNonVoid && element.returnType is VoidType)) {
         return;
       }
+      // Don't suggest wildcard local functions.
+      if (element.name == '_') return;
       var matcherScore = state.matcher.score(element.displayName);
       if (matcherScore != -1) {
         var suggestion = LocalFunctionSuggestion(
@@ -1918,6 +1928,7 @@ class DeclarationHelper {
 
   /// Adds a suggestion for the local variable represented by the [element].
   void _suggestVariable(LocalVariableElement element) {
+    if (element.isWildcardVariable) return;
     if (visibilityTracker.isVisible(element: element, importData: null)) {
       if (mustBeConstant && !element.isConst) {
         return;

pkg/analysis_server/test/services/completion/dart/declaration/wildcard_variables_test.dart

@@ -9,6 +9,7 @@ import '../../../../client/completion_driver_test.dart';
 void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(WildcardFieldTest);
+    defineReflectiveTests(WildcardForLoopTest);
     defineReflectiveTests(WildcardImportPrefixTest);
     defineReflectiveTests(WildcardLocalVariableTest);
     defineReflectiveTests(WildcardParameterTest);
@@ -42,7 +43,6 @@ suggestions
 ''');
   }
 
-  @FailingTest(reason: "the local '_' is shadowing the field")
   Future<void> test_argumentList_withLocal() async {
     await computeSuggestions('''
 void p(Object o) {}
@@ -62,6 +62,45 @@ suggestions
   }
 }
 
+@reflectiveTest
+class WildcardForLoopTest extends AbstractCompletionDriverTest {
+  @override
+  Set<String> allowedIdentifiers = {'_'};
+
+  @override
+  bool get includeKeywords => false;
+
+  Future<void> test_forEach_argumentList() async {
+    await computeSuggestions('''
+void p(Object o) {}
+
+void f() {
+  for (var _ in []) {
+    p(^);
+  }
+}
+''');
+    assertResponse('''
+suggestions
+''');
+  }
+
+  Future<void> test_forParts_argumentList() async {
+    await computeSuggestions('''
+void p(Object o) {}
+
+void f() {
+  for (var _ = 0; ;) {
+    p(^);
+  }
+}
+''');
+    assertResponse('''
+suggestions
+''');
+  }
+}
+
 @reflectiveTest
 class WildcardImportPrefixTest extends AbstractCompletionDriverTest {
   @override
@@ -70,7 +109,6 @@ class WildcardImportPrefixTest extends AbstractCompletionDriverTest {
   @override
   bool get includeKeywords => false;
 
-  @FailingTest(reason: "'_' shouldn't be suggested")
   Future<void> test_argumentList() async {
     newFile('$testPackageLibPath/ext.dart', '''
 extension ES on String {
@@ -125,7 +163,6 @@ class WildcardLocalVariableTest extends AbstractCompletionDriverTest {
   @override
   bool get includeKeywords => false;
 
-  @FailingTest(reason: "'_' shouldn't be suggested")
   Future<void> test_argumentList() async {
     await computeSuggestions('''
 void p(Object o) {}
@@ -136,9 +173,23 @@ void f() {
 }
 ''');
     assertResponse(r'''
-  suggestions
+suggestions
   b
     kind: localVariable
+''');
+  }
+
+  Future<void> test_argumentList_function() async {
+    await computeSuggestions('''
+void p(Object o) {}
+
+void f() {
+  _() {}
+  p(^);
+}
+''');
+    assertResponse(r'''
+suggestions
 ''');
   }
 }