Add language tests for "Private Named Parameters".

Fix #61641.

Change-Id: Id523b0015074d5cb66f5d17b089bedb501e5bc46
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/453646
Auto-Submit: Bob Nystrom <[email protected]>
Reviewed-by: Kallen Tu <[email protected]>
Commit-Queue: Bob Nystrom <[email protected]>

Author: munificent

tests/language/parameter/initializer6_test.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// Can call constructors with private names during const evaluation.
+
+// SharedOptions=--enable-experiment=private-named-parameters
+
+import 'package:expect/expect.dart';
+
+class C {
+  final String _foo;
+  final String _bar;
+
+  const C({required this._foo, required this._bar});
+}
+
+main() {
+  const c = C(foo: 'foo', bar: 'bar');
+  Expect.equals(c._foo, 'foo');
+  Expect.equals(c._bar, 'bar');
+}

tests/language/private_named_parameters/constant_expression_test.dart

@@ -0,0 +1,111 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// It's an error if a private named declaring parameter collides with an
+/// explicit instance variable with the same name. (This is just the normal
+/// error for a duplicate field, but we test it explicitly to make sure
+/// implementations are checking that for private named parameters.)
+
+// SharedOptions=--enable-experiment=private-named-parameters,primary-constructors
+
+import 'package:expect/expect.dart';
+
+/// Collide with explicitly declared field.
+class C1({required final String _foo}) {
+  final String _foo;
+  //           ^^^^
+  // [analyzer] unspecified
+  // [cfe] unspecified
+}
+
+/// Collide with previous private declaring parameter.
+class C2({required final String _foo, required final String _foo}) {}
+//                                                          ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+/// Collide with previous public declaring parameter.
+class C3({required final String foo, required final String _foo}) {}
+//                                                         ^^^^
+// [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+// [cfe] unspecified
+
+/// Collide with previous private named parameter.
+class C4({String? _foo, required final String _foo}) {}
+//                ^^^^
+// [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_NON_FIELD_PARAMETER
+// [cfe] unspecified
+//                                            ^^^^
+// [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+// [cfe] unspecified
+
+/// Collide with previous public named parameter.
+class C5({String? foo, required final String _foo}) {}
+//                                           ^^^^
+// [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+// [cfe] unspecified
+
+/// Collide with previous private positional parameter.
+class C6(String _foo, {required final String _foo}) {}
+//                                           ^^^^
+// [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+// [cfe] unspecified
+
+/// Collide with previous public positional parameter.
+class C7(String? foo, {required final String _foo}) {}
+//                                           ^^^^
+// [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+// [cfe] unspecified
+
+/// Collide with previous private initializing formal.
+class C8(this._foo, {required final String _foo}) {
+  //                                       ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+  // [cfe] unspecified
+  final String _foo;
+  //           ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+  // [cfe] unspecified
+}
+
+/// Collide with previous public initializing formal.
+class C9(this.foo, {required final String _foo}) {
+  //                                      ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+  // [cfe] unspecified
+  final String foo;
+}
+
+/// Collide with later private named parameter.
+class C10({required final String _foo, String? _foo}) {}
+//                                             ^^^^
+// [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+// [cfe] unspecified
+
+/// Collide with later public named parameter.
+class C11({required final String _foo, String? foo}) {}
+//                               ^^^^
+// [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+// [cfe] unspecified
+
+/// Collide with later private initializing formal.
+class C12({required final String _foo, required this._foo}) {
+  //                                                 ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+  // [cfe] unspecified
+  final String _foo;
+  //           ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+  // [cfe] unspecified
+}
+
+/// Collide with later public initializing formal.
+class C13({required final String _foo, required this.foo}) {
+  //                             ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+  // [cfe] unspecified
+  final String foo;
+}
+
+void main() {}

tests/language/private_named_parameters/declaring_parameter_collision_error_test.dart

@@ -0,0 +1,18 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// Private named parameters can be used with declaring private constructor
+/// parameters.
+
+// SharedOptions=--enable-experiment=private-named-parameters,primary-constructors
+
+import 'package:expect/expect.dart';
+
+class C({required final String _foo, required final String _bar});
+
+void main() {
+  var c = C(foo: 'foo', bar: 'bar');
+  Expect.equals(c._foo, 'foo');
+  Expect.equals(c._bar, 'bar');
+}

tests/language/private_named_parameters/declaring_parameter_test.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// Private named parameters can't be used in older language versions.
+
+// @dart=3.10
+
+import 'package:expect/expect.dart';
+
+class C {
+  final String _foo;
+
+  C({required this._foo});
+  //               ^^^^
+  // [analyzer] SYNTACTIC_ERROR.EXPERIMENT_NOT_ENABLED_OFF_BY_DEFAULT
+  // [cfe] This requires the experimental 'private-named-parameters' language feature to be enabled.
+}
+
+void main() {}

tests/language/private_named_parameters/feature_disabled_error_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// The type of the parameter should be inferred from the corresponding field.
+
+// SharedOptions=--enable-experiment=private-named-parameters
+
+import 'package:expect/expect.dart';
+import 'package:expect/static_type_helper.dart';
+
+class C {
+  int _x;
+  C({required this._x});
+}
+
+void main() {
+  C(x: expr(1)..expectStaticType<Exactly<int>>());
+}
+
+T expr<T>([Object? v]) => v as T;

tests/language/private_named_parameters/inferred_parameter_type_test.dart

@@ -0,0 +1,69 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// It's an error if a private named parameter collides with another parameter
+/// with the same public or private name.
+
+// SharedOptions=--enable-experiment=private-named-parameters
+
+class C {
+  String? foo;
+  final String? _foo;
+
+  // Colliding initializing formals.
+  C.a({required this._foo, required this._foo}) {}
+  //                                     ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_FIELD_FORMAL_PARAMETER
+  // [cfe] unspecified
+
+  // Collide with previous public initializing formal.
+  C.b({required this.foo, required this._foo}) {}
+  //                                    ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+  // [cfe] unspecified
+
+  // Collide with later private named.
+  C.c({required this._foo, String? _foo}) {}
+  //                               ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+  // [cfe] unspecified
+  //                               ^^^^
+  // [analyzer] SYNTACTIC_ERROR.PRIVATE_NAMED_NON_FIELD_PARAMETER
+  // [cfe] unspecified
+
+  // Collide with later public named.
+  C.d({required this._foo, String? foo}) {}
+  //                 ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+  // [cfe] unspecified
+
+  // Collide with previous private named.
+  C.e({String? _foo, required this._foo}) {}
+  //           ^^^^
+  // [analyzer] SYNTACTIC_ERROR.PRIVATE_NAMED_NON_FIELD_PARAMETER
+  // [cfe] unspecified
+  //                               ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+  // [cfe] unspecified
+
+  // Collide with previous public named.
+  C.f({String? foo, required this._foo}) {}
+  //                              ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+  // [cfe] unspecified
+
+  // Collide with previous private positional.
+  C.g(String _foo, {required this._foo}) {}
+  //                              ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.DUPLICATE_DEFINITION
+  // [cfe] unspecified
+
+  // Collide with previous public positional.
+  C.h(String? foo, {required this._foo}) {}
+  //                              ^^^^
+  // [analyzer] COMPILE_TIME_ERROR.PRIVATE_NAMED_PARAMETER_DUPLICATE_PUBLIC_NAME
+  // [cfe] unspecified
+}
+
+void main() {}

tests/language/private_named_parameters/initializing_formal_collision_error_test.dart

@@ -0,0 +1,35 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// Private named parameters can be used on initializing formals.
+
+// SharedOptions=--enable-experiment=private-named-parameters
+
+import 'package:expect/expect.dart';
+
+class C {
+  String _foo;
+  String _bar;
+
+  C({required this._foo, required this._bar});
+}
+
+class Both {
+  String? _foo;
+  String? foo;
+
+  Both({this._foo});
+}
+
+void main() {
+  var c = C(foo: 'foo', bar: 'bar');
+  Expect.equals(c._foo, 'foo');
+  Expect.equals(c._bar, 'bar');
+
+  // If a class has both public and private instance variables, the initializing
+  // formal always refers to the private one.
+  var b = Both(foo: 'foo');
+  Expect.equals(b._foo, 'foo');
+  Expect.equals(b.foo, null);
+}

tests/language/private_named_parameters/initializing_formal_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// Can call constructors with private names as metadata annotations.
+
+// SharedOptions=--enable-experiment=private-named-parameters
+
+import 'package:expect/expect.dart';
+
+class C {
+  final String _foo;
+  final String _bar;
+
+  const C({required this._foo, required this._bar})
+      : assert(_foo == 'foo'),
+        assert(_bar == 'bar');
+}
+
+@C(foo: 'foo', bar: 'bar')
+void main() {}

tests/language/private_named_parameters/metadata_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// A private named parameter must refer to an instance variable with the same
+/// private name.
+
+// SharedOptions=--enable-experiment=private-named-parameters
+
+class C {
+  C({this._unknown});
+  //      ^^^^^^^^
+  // [analyzer] unspecified
+  // [cfe] unspecified
+
+  // There is a public field with the name, but that isn't what the private
+  // name refers to.
+  String? unknown;
+}
+
+void main() {}