False positive for `library_private_types_in_public_api` in private typedefs

[Albert221]

typedef _PrivateInt = int;

void publicMethod(_PrivateInt param) {}

This complains about library_private_types_in_public_api.

I'm not using private type. I'm just using a private typedef, but the typedef resolves to a public type. I expect to not trigger this lint with private typedefs.

Dart SDK version: 3.5.3 (stable) (Wed Sep 11 16:22:47 2024 +0000) on "macos_arm64"

[lrhn]

Whether it works as intended is a question of intent.

The DartDoc would likely be showing the _PrivateInt name, which the reader wouldn't be able to see the type of since the typedef isn't part of the DartDoc. That's one reason to not use private types in public APIs, and probably the best one.

Otherwise it's just a type that the API client can't work with. That's annoying too.

[bwilkerson]

DartDoc isn't the only place where this type would show up. In most of our IDE tooling we display the name of the typedef, not the type that the typedef is an equivalent for.

The reason that DartDoc and the IDE tooling do this is because we're assuming that most users are using typedefs as a way of abstracting from the actual type. Using a privately named typedef in a public API destroys that abstraction because users of the API are required to figure out what the actual type of the parameter is.

If your intent for using a typedef is different, then this lint probably isn't what you're looking for.

I believe that the lint is working as intended, so I'm going to close this issue.

[ChaserVasya]

@bwilkerson
See on my case.

Snippet

final _key = Object();

typedef _ZoneValue = SomeType;

class SomeClass {
  _ZoneValue get _value => Zone.current[_key]; // assignment _ZoneValue to dynamic returned value
     
  void call( _ZoneValue value){
     runZonedGuarded(
      fn,
      zoneValues: {_key: value}
    );
   }

 fn(){
   _value.someTypeMethod();
 }
}

Meaning

I create typedef to strictly bind a call.value SomeType to Zone.current[_key].
Imagine that snippet without typedef:

  SomeType get _value => ...
  call(SomeType value){..}

Then I change it to

  SomeType get _value => ...
  call(AnotherType value){..}

And forget to change SomeType get _value .
Analyzer doesn't show any error. And _value.someTypeMethod() throws error in runtime.
But if I use _ZoneValue analyzer shows red error on _value.someTypeMethod().

Question

What should I do to change SomeType only in one place without using private typedef?

Also

I dont use the DartDocs.

AND

In most of our IDE tooling we display the name of the typedef

I use Android Studio and it doesn't use a typedef any where. For example, in a popup.

sdk

Dart SDK version: 3.5.4 (stable) (Wed Oct 16 16:18:51 2024 +0000) on "macos_arm64"

[bwilkerson]

What should I do to change SomeType only in one place without using private typedef?

I can't answer that question without more information. What I do know is that SomeClass.call is a public method, but no callers outside the library in which SomeClass is defined can invoke the call method without using whatever type _ZoneValue is defined to be. If you use the call method outside of this library then you are already unable to change SomeType in one place without having to convert the invocation sites to pass in the new value. In other words, _ZoneValue is a leaky abstraction, and if abstracting the type is why you created a typedef, then it's really a failure and the lint has correctly found it for you.

If you're only invoking call from within this library, then you could consider making it a library-private name, even though that removes the possibility of dropping the name of the method at call sites.

If you're invoking it outside of this library, then consider making _ZoneValue be a public type.