delay extension reduces type detection (for Observable.create series)

[samuelchou]

It seems that kotlin type recognition for Observable.create extension series will fail, after adding delay functions.

For example, consider code below:

data class User(val id: String, val name: String, val age: Int)

val exampleUser("test0001", "Samuel", 27)

fun getUserById(id: String): Single<User> {
    return Single.create { single ->
         exampleUser.copy(id = id).let { single.onSuccess(it) }
    }
}

Everything works fine.

Now, if I add .delay behind:

fun getUserById(id: String): Single<User> {
    return Single.create { single ->
         exampleUser.copy(id = id).let { single.onSuccess(it) }
    }.delay(500, TimeUnit.MILLISECDONDS)
}

And then build it. The editor would throw build errors at Single.create line:

at end of `Single.create`:
Not enough information to infer type variable T

at start of `single`:
Cannot infer a type for this parameter. Please specify it explicitly.

If I specify the type, the build errors will disappear:

fun getUserById(id: String): Single<User> {
    return Single.create<User> { single ->
         exampleUser.copy(id = id).let { single.onSuccess(it) }
    }.delay(500, TimeUnit.MILLISECDONDS)
}

However, some editor/kotlin plugin might suggest to "Remove explicit type arguments" then.

These errors seems not only happen at Single.create, but also at Observable.create. I guess the errors happen in all .create series?

Versions

I'm using 3.0.1 in Android Studio.

All Rx related version:

implementation 'io.reactivex.rxjava3:rxkotlin:3.0.1'
implementation 'io.reactivex.rxjava3:rxandroid:3.0.0'
implementation 'com.uber.rxdogtag2:rxdogtag:2.0.1'
implementation 'com.squareup.retrofit2:adapter-rxjava3:2.9.0'
implementation 'androidx.room:room-rxjava3:2.4.1'

The editor and plugin version:

Android Studio Chipmunk | 2021.2.1 Patch 1
Build #AI-212.5712.43.2112.8609683, built on May 19, 2022

Kotlin Plugin:
212-1.7.10-release-333-AS5457.46