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Nov 5, 2025
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#3203. Add tests for private named parameters #3377

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#3203. Add tests for private named parameters
sgrekhov Oct 31, 2025
f19fc94
Add a case with the initializer list
sgrekhov Oct 31, 2025
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188 changes: 188 additions & 0 deletions VM/private_named_parameters_t01.dart
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Original file line number Diff line number Diff line change
@@ -0,0 +1,188 @@
// 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.

/// @assertion We let users use a private name in a named parameter when the
/// parameter also initializes or declares a field. The compiler removes the `_`
/// from the argument name but keeps it for the corresponding field.
///
/// @description Check that private named parameters can be debugged.
/// @author [email protected]

// SharedOptions=--enable-experiment=declaring-constructors,private-named-parameters

import 'dart:developer';
import 'package:vm_service/vm_service.dart';

import '../../../../pkg/vm_service/test/common/service_test_common.dart';
import '../../../../pkg/vm_service/test/common/test_helper.dart';
import '../Utils/expect.dart';

// AUTOGENERATED START
//
// Update these constants by running:
//
// dart pkg/vm_service/test/update_line_numbers.dart tests/co19/src/VM/private_named_parameters_t01.dart
//
const LINE_A = 37;
const LINE_B = 41;
const LINE_C = 45;
const LINE_D = 46;
const LINE_E = 47;
// AUTOGENERATED END

class C1({var String _x}); // LINE_A

class C2 {
String _x;
C2({required this._x}); // LINE_B
}

class C3 {
int _x, _y;
C3({required this._x}) : _y = _x + 1; // LINE_C
}

void testeeMain() {
debugger(); // LINE_D
C1(x: "xxx"); // LINE_E
C2(x: "yyy"); // LINE_F
C3(x: 1); // LINE_G
}

final tests = <IsolateTest>[
hasStoppedAtBreakpoint,
stoppedAtLine(LINE_D),
stepInto,
stoppedAtLine(LINE_E),
stepInto,
stoppedAtLine(LINE_A),
(VmService service, IsolateRef isolateRef) async {
final isolateId = isolateRef.id!;
final xRef1 =
await service.evaluateInFrame(isolateId, 0, '_x') as InstanceRef;
Expect.equals("null", xRef1.valueAsString);
final xRef2 =
await service.evaluateInFrame(isolateId, 0, 'this._x') as InstanceRef;
Expect.equals("null", xRef2.valueAsString);
},
stepInto,
(VmService service, IsolateRef isolateRef) async {
final isolateId = isolateRef.id!;
final xRef1 =
await service.evaluateInFrame(isolateId, 0, '_x') as InstanceRef;
Expect.equals('xxx', xRef1.valueAsString);
final xRef2 =
await service.evaluateInFrame(isolateId, 0, 'this._x') as InstanceRef;
Expect.equals('xxx', xRef2.valueAsString);
final xRef3 = await service.evaluateInFrame(isolateId, 0, 'x');
Expect.isTrue(xRef3 is ErrorRef);
final xRef4 = await service.evaluateInFrame(isolateId, 0, 'this.x');
Expect.isTrue(xRef4 is ErrorRef);
},
stepInto,
stoppedAtLine(LINE_F),
stepInto,
stoppedAtLine(LINE_B),
(VmService service, IsolateRef isolateRef) async {
final isolateId = isolateRef.id!;
final xRef1 =
await service.evaluateInFrame(isolateId, 0, '_x') as InstanceRef;
Expect.equals("null", xRef1.valueAsString);
final xRef2 =
await service.evaluateInFrame(isolateId, 0, 'this._x') as InstanceRef;
Expect.equals("null", xRef2.valueAsString);
},
stepInto,
(VmService service, IsolateRef isolateRef) async {
final isolateId = isolateRef.id!;
final xRef1 =
await service.evaluateInFrame(isolateId, 0, '_x') as InstanceRef;
Expect.equals('yyy', xRef1.valueAsString);
final xRef2 =
await service.evaluateInFrame(isolateId, 0, 'this._x') as InstanceRef;
Expect.equals('yyy', xRef2.valueAsString);
final xRef3 = await service.evaluateInFrame(isolateId, 0, 'x');
Expect.isTrue(xRef3 is ErrorRef);
final xRef4 = await service.evaluateInFrame(isolateId, 0, 'this.x');
Expect.isTrue(xRef4 is ErrorRef);
},

stepInto,
stoppedAtLine(LINE_G),
stepInto,
stoppedAtLine(LINE_C),
(VmService service, IsolateRef isolateRef) async {
final isolateId = isolateRef.id!;
final xRef1 =
await service.evaluateInFrame(isolateId, 0, '_x') as InstanceRef;
Expect.equals("null", xRef1.valueAsString);
final xRef2 =
await service.evaluateInFrame(isolateId, 0, 'this._x') as InstanceRef;
Expect.equals("null", xRef2.valueAsString);
Comment on lines +119 to +122
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@nshahan nshahan Oct 31, 2025

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It is confusing to me that we expect _x and this._x to both be null at this time. Why?

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@sgrekhov sgrekhov Nov 3, 2025

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Based on the current behaviour of

class C {
  String x;
  C(this.x);
}

x is null at this step. Therefore, I believe, that in this test _x also should be null.

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@eernstg eernstg Nov 3, 2025

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If the current location in code is the initializer list (we could add an initializer list, or we might have stopped at a breakpoint "in the initializer list" even though it's empty, which could be the way the VM sees it) then x would denote the parameter. In contrast, at any location with access to this, including the body of the constructor (if any), x would denote the instance variable, and so would this.x.

The same would be true with _x.

If the current position in code is the initializer list it might still be possible to access the instance variables of the enclosing object using terms like this.x or this._x. The language doesn't allow us to do that, but the debugger might.

So I've argued that we should at least know how it's supposed to work, and preferably look at the treatment of both the parameter and the instance variable in situations where it is the intention that both can be viewed and possibly modified.

final xRef3 =
await service.evaluateInFrame(isolateId, 0, '_y') as InstanceRef;
Expect.equals("null", xRef3.valueAsString);
final xRef4 =
await service.evaluateInFrame(isolateId, 0, 'this._y') as InstanceRef;
Expect.equals("null", xRef4.valueAsString);
},
stepInto,
(VmService service, IsolateRef isolateRef) async {
final isolateId = isolateRef.id!;
final xRef1 =
await service.evaluateInFrame(isolateId, 0, '_x') as InstanceRef;
Expect.equals('1', xRef1.valueAsString);
final xRef2 =
await service.evaluateInFrame(isolateId, 0, 'this._x') as InstanceRef;
Expect.equals('1', xRef2.valueAsString);
final xRef3 =
await service.evaluateInFrame(isolateId, 0, '_y') as InstanceRef;
Expect.equals('null', xRef3.valueAsString);
final xRef4 =
await service.evaluateInFrame(isolateId, 0, 'this._y') as InstanceRef;
Expect.equals('null', xRef3.valueAsString);

final xRef5 = await service.evaluateInFrame(isolateId, 0, 'x');
Expect.isTrue(xRef5 is ErrorRef);
final xRef6 = await service.evaluateInFrame(isolateId, 0, 'this.x');
Expect.isTrue(xRef6 is ErrorRef);
final xRef7 = await service.evaluateInFrame(isolateId, 0, 'y');
Expect.isTrue(xRef7 is ErrorRef);
final xRef8 = await service.evaluateInFrame(isolateId, 0, 'this.y');
Expect.isTrue(xRef8 is ErrorRef);
},
stepInto,
(VmService service, IsolateRef isolateRef) async {
final isolateId = isolateRef.id!;
final xRef1 =
await service.evaluateInFrame(isolateId, 0, '_x') as InstanceRef;
Expect.equals('1', xRef1.valueAsString);
final xRef2 =
await service.evaluateInFrame(isolateId, 0, 'this._x') as InstanceRef;
Expect.equals('1', xRef2.valueAsString);
final xRef3 =
await service.evaluateInFrame(isolateId, 0, '_y') as InstanceRef;
Expect.equals('2', xRef3.valueAsString);
final xRef4 =
await service.evaluateInFrame(isolateId, 0, 'this._y') as InstanceRef;
Expect.equals('2', xRef3.valueAsString);

final xRef5 = await service.evaluateInFrame(isolateId, 0, 'x');
Expect.isTrue(xRef5 is ErrorRef);
final xRef6 = await service.evaluateInFrame(isolateId, 0, 'this.x');
Expect.isTrue(xRef6 is ErrorRef);
final xRef7 = await service.evaluateInFrame(isolateId, 0, 'y');
Expect.isTrue(xRef7 is ErrorRef);
final xRef8 = await service.evaluateInFrame(isolateId, 0, 'this.y');
Expect.isTrue(xRef8 is ErrorRef);
},
];

void main([args = const <String>[]]) => runIsolateTests(
args,
tests,
'private_named_parameters_t01.dart',
pauseOnExit: true,
testeeConcurrent: testeeMain,
);
69 changes: 69 additions & 0 deletions VM/private_named_parameters_t02.dart
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Open in desktop
Original file line number Diff line number Diff line change
@@ -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.

/// @assertion We let users use a private name in a named parameter when the
/// parameter also initializes or declares a field. The compiler removes the `_`
/// from the argument name but keeps it for the corresponding field.
///
/// @description Check that private named parameters are allowed in VM
/// expression evaluation.
/// @author [email protected]

// SharedOptions=--enable-experiment=declaring-constructors,private-named-parameters

import 'dart:developer';

import 'package:vm_service/vm_service.dart';

import '../../../../pkg/vm_service/test/common/service_test_common.dart';
import '../../../../pkg/vm_service/test/common/test_helper.dart';
import '../Utils/expect.dart';

class C1({var String _x});

class C2 {
String _x;
C2({required this._x});
}

void testeeMain() {
final c1 = C1(x: "one");
final c2 = C2(x: "two");
debugger();
}

final tests = <IsolateTest>[
hasStoppedAtBreakpoint,

// Test interaction of expression evaluation with private named parameters.
(VmService service, IsolateRef isolateRef) async {
final isolateId = isolateRef.id!;

InstanceRef response =
await service.evaluateInFrame(isolateId, 0, 'c1._x') as InstanceRef;
Expect.equals('one', response.valueAsString);

response =
await service.evaluateInFrame(isolateId, 0, 'c2._x') as InstanceRef;
Expect.equals('two', response.valueAsString);

response =
await service.evaluateInFrame(isolateId, 0, 'C1(x: "zero")._x')
as InstanceRef;
Expect.equals('zero', response.valueAsString);

response =
await service.evaluateInFrame(isolateId, 0, 'C2(x: "0")._x')
as InstanceRef;
Expect.equals('0', response.valueAsString);
},
];

void main([args = const <String>[]]) => runIsolateTests(
args,
tests,
'private_named_parameters_t02.dart',
pauseOnExit: true,
testeeConcurrent: testeeMain,
);