dynamic field throws 'Null check operator used on a null value'

[techouse]

Describe the issue

I have a dynamic field and the generated code throws a Null check operator used on a null value exception.

Possibly a result of #69 (comment)

Environment details

Dart 2.18.6

To Reproduce

Steps to reproduce the behaviour:

Declare a dynamic field in a class, i.e.

final dynamic action;

and the generated code is

action: action == const $CopyWithPlaceholder() || action == null
        // ignore: unnecessary_non_null_assertion
        ? _value.action!
        // ignore: cast_nullable_to_non_nullable
        : action as dynamic,

This will throw an exception when running unit tests

Null check operator used on a null value
package:alfred_workflow/src/models/alfred_item.g.dart 211:26         _$AlfredItemCWProxyImpl.call
test/fixtures/models/alfred_item_fixture.dart 93:33                  AlfredItemFactory.uid.<fn>
package:data_fixture_dart/factories/fixture_factory.dart 31:30       FixtureFactory.redefine.<fn>
package:data_fixture_dart/definitions/fixture_definition.dart 24:26  FixtureDefinition.makeMany.<fn>
dart:core                                                            new List.generate
package:data_fixture_dart/definitions/fixture_definition.dart 22:12  FixtureDefinition.makeMany
test/unit/models/alfred_items_test.dart 15:10                        main.<fn>

The exception above refers to the line

? _value.action!

where a null check operator (!) is used on dynamic

Expected behaviour

No exception and nullability properly handled on a dynamic field.

Additional context

The only workaround I have found is to use Object? instead of dynamic, like so:

final Object? action;

and the generated code becomes

action: action == const $CopyWithPlaceholder()
        ? _value.action
        // ignore: cast_nullable_to_non_nullable
        : action as Object?,

You can see the workaround in action here

[numen31337]

Hi @techouse,
I attempted to recreate the issue you reported, but I was unable to reproduce the crash you experienced. It's possible that the problem was fixed with the latest version of Dart or that I made a mistake during my testing. Can you take a look at the following test and let me know if it addresses the issue you described?

[techouse]

It does not crash, it just throws all these error messages.

[numen31337]

@techouse Looks like I'm having difficulty replicating the issue and I am wondering if you can guide me on how to see the relevant error messages.

[techouse]

@numen31337 of course :) The warning only appears when you actually run the code. In the tests it's muted.

I have created a repo demonstrating it here https://github.com/techouse/copy_with_extension_nullability_issue_demo

Way to reproduce it:

1. clone the repo
2. install the dependencies
3. execute

dart run bin/main.dart

This will print

lib/foo.g.dart:53:20: Warning: Operand of null-aware operation '!' has type 'String' which excludes null.
          ? _value.name!
                   ^
Foo(name: bar, value: baz)

[numen31337]

For the record, the problem mentioned here is not reflected in #74 (comment). The #74 (comment) is representative of the issue #75 which is a different one. This ticket pertains specifically to instances where an object has a dynamic field that was initialised as null, and subsequently using copyWith on such an object will crash and result in the error message Null check operator used on a null value mentioned earlier.

Test case:

import 'package:copy_with_extension/copy_with_extension.dart';
import 'package:test/test.dart' show test, expect;

part 'gen_nullability_test.g.dart';

@CopyWith()
class TestNullability {
  TestNullability(
    int this.nullableWithNonNullableConstructor,
    this.dynamicField,
    this.integers,
  );

  final int? nullableWithNonNullableConstructor;
  final dynamic dynamicField;
  final List<int> integers;
}

void main() {
  test('TestNullability', () {
    expect(TestNullability(1, null, [1]).copyWith.integers([2]).dynamicField, null);
  });
}

Leads to the crash here:

      dynamicField == const $CopyWithPlaceholder() || dynamicField == null
          // ignore: unnecessary_non_null_assertion
          ? _value.dynamicField! // <--- CRASH
          // ignore: cast_nullable_to_non_nullable
          : dynamicField as dynamic,

[techouse]

@numen31337 correct. My memory on this issue is not the freshest anymore.

I have added more tests into another branch in the same repo https://github.com/techouse/copy_with_extension_nullability_issue_demo/tree/issue-74

Running dart test will produce

$ dart test         
00:00 +1 -1: test/foo_test.dart: issue-74-no-dynamic-value copyWith [E]                                                                                                                                                                
  Null check operator used on a null value
  package:nullability_issue/foo.g.dart 58:25  _$FooCWProxyImpl.call
  test/foo_test.dart 28:28                    main.<fn>.<fn>
  

To run this test again: /usr/local/Caskroom/flutter/3.7.5/flutter/bin/cache/dart-sdk/bin/dart test test/foo_test.dart -p vm --plain-name 'issue-74-no-dynamic-value copyWith'
00:00 +3 -2: test/foo_test.dart: issue-74-null-dynamic-value copyWith [E]                                                                                                                                                              
  Null check operator used on a null value
  package:nullability_issue/foo.g.dart 58:25  _$FooCWProxyImpl.call
  test/foo_test.dart 59:28                    main.<fn>.<fn>
  

To run this test again: /usr/local/Caskroom/flutter/3.7.5/flutter/bin/cache/dart-sdk/bin/dart test test/foo_test.dart -p vm --plain-name 'issue-74-null-dynamic-value copyWith'
00:00 +5 -3: test/foo_test.dart: issue-74-random-null-value copyWith [E]                                                                                                                                                               
  Null check operator used on a null value
  package:nullability_issue/foo.g.dart 58:25  _$FooCWProxyImpl.call
  test/foo_test.dart 88:28                    main.<fn>.<fn>
  

To run this test again: /usr/local/Caskroom/flutter/3.7.5tter/bin/cache/dart-sdk/bin/dart test test/foo_test.dart -p vm --plain-name 'issue-74-random-null-value copyWith'
00:00 +5 -3: Some tests failed.                                                                                                                                                                                                        

Consider enabling the flag chain-stack-traces to receive more detailed exceptions.
For example, 'dart test --chain-stack-traces'.