[wildcards] improve _ type param handling

See: #56361

Change-Id: Ic3be09014afc095490d9332bd124843b5a65e1cd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/381385
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

@@ -1931,7 +1931,9 @@ class DeclarationHelper {
   /// Adds a suggestion for each of the [typeParameters].
   void _suggestTypeParameters(List<TypeParameterElement> typeParameters) {
     for (var parameter in typeParameters) {
-      _suggestTypeParameter(parameter);
+      if (!_isWildcard(parameter.name)) {
+        _suggestTypeParameter(parameter);
+      }
     }
   }
 
@@ -2180,7 +2182,9 @@ class DeclarationHelper {
     for (var typeParameter in typeParameters.typeParameters) {
       var element = typeParameter.declaredElement;
       if (element != null) {
-        _suggestTypeParameter(element);
+        if (!_isWildcard(element.name)) {
+          _suggestTypeParameter(element);
+        }
       }
     }
   }

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

@@ -15,12 +15,13 @@ void main() {
     defineReflectiveTests(WildcardLocalVariableTest);
     defineReflectiveTests(WildcardParameterTest);
     defineReflectiveTests(WildcardTopLevelVariableTest);
+    defineReflectiveTests(WildcardTypeParameterTest);
   });
 }
 
 class AbstractWildCardTest extends AbstractCompletionDriverTest {
   @override
-  Set<String> allowedIdentifiers = {'_', '__', '___'};
+  Set<String> allowedIdentifiers = {'_', '__', '___', 'T'};
 
   @override
   bool get includeKeywords => false;
@@ -353,3 +354,80 @@ suggestions
 ''');
   }
 }
+
+@reflectiveTest
+class WildcardTypeParameterTest extends AbstractWildCardTest {
+  Future<void> test_constructor_formalParameterList() async {
+    await computeSuggestions('''
+class C<T, _> {
+  C(^);
+}
+''');
+    assertResponse('''
+suggestions
+  T
+    kind: typeParameter
+''');
+  }
+
+  Future<void> test_extensionMethod_formalParameterList() async {
+    await computeSuggestions('''
+extension E<_, T> on List {
+  void f(^) {}
+}
+''');
+    assertResponse('''
+suggestions
+  T
+    kind: typeParameter
+''');
+  }
+
+  Future<void> test_extensionType__representationDeclaration() async {
+    await computeSuggestions('''
+extension type ET<_, T, _ extends num>(^) {}
+''');
+    assertResponse('''
+suggestions
+  T
+    kind: typeParameter
+''');
+  }
+
+  Future<void> test_extensionType_method_formalParameterList() async {
+    await computeSuggestions('''
+extension type ET<_, T, _ extends num>(num n) {
+  f(^) {}
+}
+''');
+    assertResponse('''
+suggestions
+  T
+    kind: typeParameter
+''');
+  }
+
+  Future<void> test_function_formalParameterList() async {
+    await computeSuggestions('''
+f<T,_>(^) {}
+''');
+    assertResponse('''
+suggestions
+  T
+    kind: typeParameter
+''');
+  }
+
+  Future<void> test_method_formalParameterList() async {
+    await computeSuggestions('''
+class C<T, _> {
+  void m(^);
+}
+''');
+    assertResponse('''
+suggestions
+  T
+    kind: typeParameter
+''');
+  }
+}