use_super_parameters and unused_element conflict in private Flutter widgets

[maxlapides]

Assumptions:

• Flutter 3.0
• user_super_parameters lint rule is enabled
• unused_element analyzer rule is enabled

This code chunk produces an analyzer issue:

class _MyWidget extends StatelessWidget {
  const _MyWidget({super.key});

  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

"A value for optional parameter 'key' isn't ever given. Try removing the unused parameter."

But, when the same widget is not private, there is no issue:

class MyWidget extends StatelessWidget {
  const MyWidget({super.key});

  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

I would like to keep the super.key on the private widgets, but I also want to keep the unused_element rule enabled. Is there any way to achieve this?

❯ flutter doctor -v
[✓] Flutter (Channel stable, 3.0.0, on macOS 12.3.1 21E258 darwin-arm, locale en-US)
    • Flutter version 3.0.0 at /Users/maxlapides/fvm/versions/3.0.0
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision ee4e09cce0 (2 days ago), 2022-05-09 16:45:18 -0700
    • Engine revision d1b9a6938a
    • Dart version 2.17.0
    • DevTools version 2.12.2

[✓] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
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    • Platform android-31, build-tools 31.0.0
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[✓] Xcode - develop for iOS and macOS (Xcode 13.3.1)
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    • CocoaPods version 1.11.3

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    • Java version OpenJDK Runtime Environment (build 11.0.11+0-b60-7772763)

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    • Flutter extension version 3.40.0

[✓] Connected device (3 available)
    • iPhone 13 (mobile) • 8A362B17-9737-4B87-B0E4-77BF160D0A50 • ios            •
      com.apple.CoreSimulator.SimRuntime.iOS-15-4 (simulator)
    • macOS (desktop)    • macos                                • darwin-arm64   • macOS 12.3.1 21E258 darwin-arm
    • Chrome (web)       • chrome                               • web-javascript • Google Chrome 101.0.4951.64

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• No issues found!

[darshankawar]

Thanks for the report. Using private widget, flutter analyze gives below log:

Analyzing testdemo...                                                   

   info • The annotation 'Timeout' can only be used on libraries • integration_test/app_test.dart:7:2 • invalid_annotation_target
   info • A value for optional parameter 'key' isn't ever given • lib/main.dart:9:26 • unused_element

While non-private widget doesn't give the same log.

Keeping this issue open for further insights from the team.

stable, master flutter doctor -v

[✓] Flutter (Channel stable, 3.0.0, on macOS 12.2.1 21D62 darwin-x64, locale
    en-GB)
    • Flutter version 3.0.0 at /Users/dhs/documents/fluttersdk/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision ee4e09cce0 (2 days ago), 2022-05-09 16:45:18 -0700
    • Engine revision d1b9a6938a
    • Dart version 2.17.0
    • DevTools version 2.12.2

[!] Xcode - develop for iOS and macOS (Xcode 12.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    ! Flutter recommends a minimum Xcode version of 13.
      Download the latest version or update via the Mac App Store.
    • CocoaPods version 1.11.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] VS Code (version 1.62.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.21.0

[✓] Connected device (5 available)
    • SM G975F (mobile)       • RZ8M802WY0X • android-arm64   • Android 11 (API 30)
    • Darshan's iphone (mobile)  • 21150b119064aecc249dfcfe05e259197461ce23 •
      ios            • iOS 14.4.1 18D61
    • iPhone 12 Pro Max (mobile) • A5473606-0213-4FD8-BA16-553433949729     •
      ios            • com.apple.CoreSimulator.SimRuntime.iOS-14-3 (simulator)
    • macOS (desktop)            • macos                                    •
      darwin-x64     • Mac OS X 10.15.4 19E2269 darwin-x64
    • Chrome (web)               • chrome                                   •
      web-javascript • Google Chrome 98.0.4758.80

[✓] HTTP Host Availability
    • All required HTTP hosts are available

! Doctor found issues in 1 category.

[✓] Flutter (Channel master, 3.1.0-0.0.pre.663, on macOS 12.2.1 21D62
    darwin-x64, locale en-GB)
    • Flutter version 3.1.0-0.0.pre.663 at
      /Users/dhs/documents/fluttersdk/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision a298bdb417 (64 minutes ago), 2022-05-11 23:14:08 -0400
    • Engine revision 0673b781d2
    • Dart version 2.18.0 (build 2.18.0-106.0.dev)
    • DevTools version 2.13.1
    
[!] Xcode - develop for iOS and macOS (Xcode 12.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    ! Flutter recommends a minimum Xcode version of 13.
      Download the latest version or update via the Mac App Store.
    • CocoaPods version 1.11.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] VS Code (version 1.62.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.21.0

[✓] Connected device (5 available)
    • SM G975F (mobile)       • RZ8M802WY0X • android-arm64   • Android 11 (API 30)
    • Darshan's iphone (mobile)  • 21150b119064aecc249dfcfe05e259197461ce23 •
      ios            • iOS 14.4.1 18D61
    • iPhone 12 Pro Max (mobile) • A5473606-0213-4FD8-BA16-553433949729     •
      ios            • com.apple.CoreSimulator.SimRuntime.iOS-14-3 (simulator)
    • macOS (desktop)            • macos                                    •
      darwin-x64     • Mac OS X 10.15.4 19E2269 darwin-x64
    • Chrome (web)               • chrome                                   •
      web-javascript • Google Chrome 98.0.4758.80

[✓] HTTP Host Availability
    • All required HTTP hosts are available

! Doctor found issues in 1 category.

[goderbauer]

The linter, which implements these lint rules, may be a more appropriate place for this discussion: https://github.com/dart-lang/linter

For private widgets, the analyzer can determine with certainty that nobody is ever passing in a key to the widget. That's why the parameter gets flagged. For public widgets, no such guarantee can be given because some other code may import this code and pass in a key.

[maxlapides]

Thanks for the input @goderbauer! I see, I now understand why this occurring from a technical perspective, but I'd still like to keep the super.key on the private widgets while also taking advantage of the unused_element analysis. So, I re-opened this issue on the Dart linter project: dart-lang/sdk#49025. We can move this conversation over there, and I'll close this ticket.