Having two clauses in a when statement or two branches in an if chain with the same implementation is at best duplicate code, and at worst a coding error. If the same logic is truly needed for both instances, then in an if chain they should be combined, or for a when, duplicates should be refactored.

Noncompliant Code Example

fun s1871(x: Int) {
    when (x) {
        1 -> {
            val y = x / 2
            print(y)
        }
        2 -> {
            val y = x / 2
            print(y)
        }
    }
}

Exceptions

Blocks in an if chain that contain a single line of code are ignored, as are blocks in a when statement that contain a single line of code with or without a following break.

if (a == 1) {
    doSomething()  //no issue, usually this is done on purpose to increase the readability
} else if (a == 2) {
    doSomethingElse()
} else {
    doSomething()
}

But this exception does not apply to if chains without else-s, or to when-es without else clauses when all branches have the same single line of code. In case of if chains with else-s, or of when-es with default clauses, rule {rule:kotlin:S3923} raises a bug.

if (a == 1) {
  doSomething()  //Noncompliant, this might have been done on purpose but probably not
} else if (a == 2) {
  doSomething()
}