Is there a rule that I can reuse for catching unus...

# detekt

[Kirill Zhukov]

Is there a rule that I can reuse for catching unused declarations? A common pattern in my codebase is to set a state like so: state = FooState. Sometimes it’s easy to typo and forget to set the state: FooState. All of my states are derived from a common State type, so wondering if there is a rule that makes sure that types of the State are used.

[chao]

I am wondering if you’d mind elaborating your example a bit - I am wondering if this is a false positive for https://detekt.dev/docs/rules/style#unusedprivatemember

[twisterrob]

This is more similar to @CheckReturnValue. I don't think there's a Detekt rule that checks dangling objects (or just never written this kind of code). @chao afaiu the use case is:

class SomethingC
object SomethingO
class Other {
    fun f() {
        this.state = SomethingO // ok, SomethingO.INSTANCE is used
        this.state = SomethingC() // ok, constructor's "return value" is used
        SomethingO // flag
        SomethingC() // flag
    }
}

[twisterrob]

@Kirill Zhukov I think you can write your own rule pretty easily with type resolution. Find all the constructor calls / object references to classes extending state, and then validate that they're part of an assignment, a function call, or return statement/expression. The only thing I don't know how to detect is .let { MyState(it) } or when { true -> MyState; else -> error() }, because these usages are not an assignment, nor a function call.

[Kirill Zhukov]

That’s right, ideally I would want something similar to @CheckReturnValue 🙂