Bazel + Arrow Failure Case

This repo is a small test case that demonstrates kt_jvm_import failing to work with the Arrow error handling library.

It specifically demonstrates using Either.

Running

There are two projects, MainWorks and MainFails. Each use Arrow in a trivial way.

MainWorks

val a = Either.Left("left")
val b = Either.Right(5)
println(a)
println(b)

val c = Either.Left("one").fold({
    println("Converting $it to two")
    "two"
}, {
    "not used"
})
println(c)

This code uses Either.Left, Either.Right, and Either.fold, all which work and compile without issue.

$ bazel run //:MainWorks
...
Left(a=left)
Right(b=5)
Converting one to two
two

MainFails

val a = Either.Right(5)
val b = a.flatMap { Either.Right(it + 1) }
println(a)
println(b)

This code uses Either.flatMap, which is defined here, and documented here.

The compiler fails to find the method.

$ bazel run //:MainFails
...
ERROR: /.../bazel-arrow-kt/BUILD:38:1: Compiling 1 Kotlin source files to MainFails.jar failed (Exit 1)
MainFails.kt:7:15: error: unresolved reference. None of the following candidates is applicable because of receiver type mismatch:
public inline fun <T, R> Array<out ???>.flatMap(transform: (???) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <R> BooleanArray.flatMap(transform: (Boolean) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <R> ByteArray.flatMap(transform: (Byte) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <R> CharArray.flatMap(transform: (Char) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <R> CharSequence.flatMap(transform: (Char) -> Iterable<???>): List<???> defined in kotlin.text
public inline fun <R> DoubleArray.flatMap(transform: (Double) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <R> FloatArray.flatMap(transform: (Float) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <R> IntArray.flatMap(transform: (Int) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <R> LongArray.flatMap(transform: (Long) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <R> ShortArray.flatMap(transform: (Short) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <T, R> Iterable<???>.flatMap(transform: (???) -> Iterable<???>): List<???> defined in kotlin.collections
public inline fun <K, V, R> Map<out ???, ???>.flatMap(transform: (Map.Entry<???, ???>) -> Iterable<???>): List<???> defined in kotlin.collections
public fun <T, R> Sequence<???>.flatMap(transform: (???) -> Sequence<???>): Sequence<???> defined in kotlin.sequences
    val b = a.flatMap { Either.Right(it + 1) }
              ^
MainFails.kt:7:38: error: unresolved reference: it
    val b = a.flatMap { Either.Right(it + 1) }
...

Fix

We found a fix:

For some reason, Either.flatMap is available via import arrow.core.flatMap. I assume the other methods are available in the same way.

See the latest commit for the change.