proposal: equality_operator_override_with_nullable_parameter

[srawlins]

equality_operator_override_with_nullable_parameter

Description

Do not override the equality operator to have a nullable parameter.

Details

No Dart implementation will ever pass null to an equality operator, so no equality operator should accept a nullable parameter. Object.== accepts an Object.

Kind

Improves readability, guards against misunderstanding...

Bad Examples

class C {
  @override
  bool operator ==(Object? other) {
    return true;
  }
}

Good Examples

class C {
  @override
  bool operator ==(Object other) {
    return true;
  }
}

Discussion

I have found a number of cases of classes which override to accept a dynamic parameter, while switching mockito-dependant tests to use code-generated mockito. Code-generated mockito includes an override for ==, which stumbles, trying to re-narrow the parameter type to Object.

This rule would more-or-less replace https://dart-lang.github.io/linter/lints/avoid_null_checks_in_equality_operators.html.

Discussion checklist

• List any existing rules this proposal modifies, complements, overlaps or conflicts with.
• List any relevant issues (reported here, the SDK Tracker, or elsewhere).
• If there's any prior art (e.g., in other linters), please add references here.
• If this proposal corresponds to Effective Dart or Flutter Style Guide advice, please call it out. (If there isn't any corresponding advice, should there be?)
• If this proposal is motivated by real-world examples, please provide as many details as you can. Demonstrating potential impact is especially valuable.

[srawlins]

Oops, found the existing issue. #58753