FileTraverser has a poor API for use by Kotlin

Overload resolution ambiguity. All these functions match.
public abstract fun breadthFirst(p0: Path!): (Mutable)Iterable<Path!>! defined in com.google.common.graph.Traverser
public abstract fun breadthFirst(p0: (Mutable)Iterable<Path!>!): (Mutable)Iterable<Path!>! defined in com.google.common.graph.Traverser

Kotlin cannot distinguish between Path and Iterable<Path> making use of this function impossible by Kotlin code.

[chaoren]

$ cat Test.kt
import com.google.common.io.MoreFiles
import java.nio.file.Path
import kotlin.io.path.Path

fun main() {
  for (path in MoreFiles.fileTraverser().breadthFirst(Path("."))) {
    println(path)
  }
}
$ wget https://repo1.maven.org/maven2/com/google/guava/guava/31.1-jre/guava-31.1-jre.jar
$ wget https://github.com/JetBrains/kotlin/releases/download/v1.7.10/kotlin-compiler-1.7.10.zip
$ unzip kotlin-compiler-1.7.10.zip
$ ./kotlinc/bin/kotlinc -cp guava-31.1-jre.jar:kotlinc/lib/kotlin-stdlib-jdk7.jar:. Test.kt

It compiles just fine.

$ ./kotlinc/bin/kotlin -cp guava-31.1-jre.jar:kotlinc/lib/kotlin-stdlib-jdk7.jar:. TestKt

It runs just fine as well.

[fzakaria]

It doesn’t show well from the snippet but what I pasted was the error the kotlin compiler was giving me. It cannot distinguish between Iterable<Path> and Path since Path also implements the Iterable Interface.

Interestingly, I got around this by doing:

MoreFiles.fileTraverser().depthFirstPreOrder(listOf(root))

If I do the path without a collection depthFirstPreOrder(root) I get the failure as mentioned above.