Spring Beans of generic interfaces with nested Kotlin type parameters are not found

Interface implementations that use nested type parameters with Kotlin types are not found as implementations. The following example fails:

package com.example.demo

import org.springframework.stereotype.Component

interface MyInterface<T> {
    fun doit(): T
}

@Component
class MyImplementation1 : MyInterface<Sequence<Int>> {
    override fun doit(): Sequence<Int> {
        TODO("not implemented")
    }
}

@Component
class MyConsumer(private val my: MyInterface<Sequence<Int>>)

The error message is:

Parameter 0 of constructor in com.example.demo.MyConsumer required a bean of type 'com.example.demo.MyInterface' that could not be found.

But if I use the (similar) Java interface Stream everything is fine:

package com.example.demo

import org.springframework.stereotype.Component
import java.util.stream.Stream

interface MyInterface<T> {
    fun doit(): T
}

@Component
class MyImplementation1 : MyInterface<Stream<Int>> {
    override fun doit(): Stream<Int> {
        TODO("not implemented")
    }
}

@Component
class MyConsumer(private val my: MyInterface<Stream<Int>>)

The application file is identical in both cases:

package com.example.demo

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class DemoApplication

fun main(args: Array<String>) {
    runApplication<DemoApplication>(*args)
}

Possibly related to #22313

Comment From: encircled

Hi,

Yes, this is the same issue as #22313, Kotlin Sequence class has out variance, which causes the problem.

Comment From: hpy1994-java

oops~

Comment From: sdeleuze

I close this issue since that's a duplicate of #22313 indeed.