False positive on UnnecessaryEventHandlerParameter

[BraisGabin]

Given this code:

internal sealed class State {
    object Loading : State()
    data class Data(val id: String) : State()
}

@Composable
internal fun MyButton(
    state: State,
    onClick: (String) -> Unit,
) {
    when (state) {
        State.Loading -> Text("Loading")
        is State.Data -> Button(onClick = { onClick(state.id) }) { Text("Click here") }
    }
}

UnnecessaryEventHandlerParameter raises an issue. But in this case the parameter is necessary because state.id is accesible because of the smart cast that you don't have in the function that call this component.

[dimsuz]

Ugh, right. Not sure how to solve this without converting this rule to use type resolution (to check that State is a sealed class - it could be defined in other file/subproject).

(I'm still a bit hesitant to use type resolution, because I feel that it's not widely adopted at the moment, but perhaps I'm wrong. And maybe putting some direct advice + instructions on enabling it in the README would help)

[BraisGabin]

Yes, to fix this we will need type resolution.

Right now I'm working on this on the detekt side:

• No experimental type solving detekt/detekt#4960
• Improve binding context management detekt/detekt#5130
• Detect type resolving rules run without type resolution classpath set detekt/detekt#3577 <- This one is the more interesting one. Once we merge Improve binding context management detekt/detekt#5130 I would be able to face that issue. This way if a user has a rule that requires type resolution active but s/he runs detekt without it s/he will get a warning to let s/he know about it.

With those type resolution will not be experimental anymore and we will inform users about the rules that they have active but they aren't working.

[dimsuz]

Great work! So I'll get started. Both in adopting type resolution in our work projects and learning to write rules for it (only saw examples in the Detekt repo, didn't try myself).

[BraisGabin]

To be honest, they are more complex. But the good part is that there are enoght examples in the detekt repo to find what you need.