[BUG]: check-unnecessary-nullable check false positive result in Tear-offs

[MorosophDude]

• Dart code metrics version: 5.4.0
• Dart sdk version: 2.18.6
• Flutter version: 3.3.10 (stable)

Please show your full configuration:

Configuration

include: package:lint/analysis_options.yaml

linter:
  rules:
    constant_identifier_names: false

analyzer:
  exclude:
    - "**/*.g.dart"
    - "**/*.freezed.dart"
  errors:
    invalid_annotation_target: ignore
    use_super_parameters: ignore

What did you do? Please include the source code example causing the issue.

All I did was run CLI command to check for unnecessary nullable

 dart run dart_code_metrics:metrics check-unnecessary-nullable lib

More Detail trying to make sense on why and what actually happened

So I have a function that validates a form and add/update an item in a list

bool validateAndAdd({int? indexOfItemToBeUpdated}) {
 // some validation logic
}

Here, if the indexOfItemToBeUpdated is null then the item will be added else item at provided index will be updated with new values.

This is how these values are called/used

// For Add
openEditorDialog(
    onSubmit: addEditController.validateAndAdd, // Notice this line
    child: const AddEditView(),
);

// For Update
openEditorDialog(
    onSubmit: () => addEditController.validateAndAdd(indexOfItemToBeUpdated: index),
    child: const AddEditView(),
);

So what is the problem?
Running

 dart run dart_code_metrics:metrics check-unnecessary-nullable lib

gives

lib/app/.../my_file_name.dart:
    method validateAndAdd has unnecessary nullable parameters
          (int? indexOfItemToBeUpdated)
          at /Users/.../my_file_name.dart:46:3

Anything else?
I change how validateAndAdd function was called for Add case
I just replaced Tear-off method of calling a function with equivalent expression function

// Using Tear-off (Old)
// openEditorDialog(
//     onSubmit: addEditController.validateAndAdd,
//     child: const AddEditView(),
// );

// Using expression function (New)
openEditorDialog(
    onSubmit: () => addEditController.validateAndAdd(),
    child: const AddEditView(),
);

and then I ran check-unnecessary-nullable command once more.
Voila! dart_code_metrics doesn't list this file anymore

Final Thought
I love using tear-offs and it would be great if dart_code_metrics supports them. This example provided above is just 1 of many places I have used tear-off and got this message. I know this might not be priority task compared to some other Open tickets and that is fine but please have a look at this when you get a chance.

Are you willing to submit a pull request to fix this bug?
No. I would love to help but I don't know where/how to start.

[incendial]

This example provided above is just 1 of many places I have used tear-off and got this message.

@MorosophDude hi, thank you for reporting the issue. Do all the places you mentioned result in the same problem or there are multiple problems with tear-offs?

[MorosophDude]

All of them have the same problem

[incendial]

Can you provide the type of onSubmit?

[MorosophDude]

Sure it has a return type of bool

Here is the function definition just in case

void openEditorDialog({
  required Widget child,
  required bool Function() onSubmit,
}) {
    // Logic to show Dialog, wrapped with WillPopScope
}

One more thing, I know it is not related in anyway but you should know I am using GetX (get: ^4.6.5)

[incendial]

@MorosophDude the fix is already in the master branch, can you test it?

One more thing, I know it is not related in anyway but you should know I am using GetX (get: ^4.6.5)

I don't think I can use this info anyhow, so, yeah, not related 🙂

[MorosophDude]

I tested the fix from master branch, and it kinda worked.

Here are the things I did.

After reading your comment I checked for new version of dart_code_metrics and saw

feat: ignore tear-off methods for avoid-unused-parameters.

in changelog of 5.4.0. (So, Step 1 and 2 just to be sure I was using the latest thing)

Step 1: flutter pub cache clean
Step 2: flutter pub get

This didn't change the result, it still showed issues in 10 files.

Remembered that master branch and the branch for pub.dev could be different. So went ahead and changed pubspec.yaml

Step 3: Replaced from

dev_dependencies:
  dart_code_metrics: ^5.4.0

to

dev_dependencies:
  dart_code_metrics:
    git:
      url: https://github.com/dart-code-checker/dart-code-metrics.git
      ref: master

This changed the result. Now it shows issues in 1 file.

Is this remaining 1 file different than other in any way?
Yes, while other 9 called the tear-off like this

openEditorDialog(
    onSubmit: addEditController.validateAndAdd,
    child: const AddEditView(),
);

this one had it called like this

openEditorDialog(
    onSubmit: employeeAddEditController
                      .employeeWorkBreakdownAddEditController
                      .validateAndAdd,
    child: const AddEditView(),
);

All other things are same, the only difference being nesting/chain of controllers.

In the mean time I will try to replicate this without using controllers (just plain function that is in the same file), if I succeed I will post it here.