Structural type support for Scala 3 (linker error)

[avdv]

Hi.

I locally published munit (scalameta/munit#477) upgrading scala-native to 0.4.3 for Scala 3.1.1.

Trying to use it though, results in a linker error:

[info] compiling 1 Scala source to /home/claudio/github/scalals/native/target/scala-3.1.1/test-classes ...
[info] Linking (2598 ms)
[error] missing symbols:
[error] * M15java.lang.ClassD8getFieldL16java.lang.StringL23java.lang.reflect.FieldEO
[error]   - from M24scala.reflect.SelectableD13selectDynamicL16java.lang.StringL16java.lang.ObjectEO
[error]   - from M42scala.reflect.Selectable$DefaultSelectableD13selectDynamicL16java.lang.StringL16java.lang.ObjectEO
[error]   - from M25scala.reflect.Selectable$D20reflectiveSelectableL16java.lang.ObjectL24scala.reflect.SelectableEO
[error]   - from M22munit.internal.Compat$D19collectionClassNameL25scala.collection.IterableL16java.lang.StringEO
[error]   - from M32munit.internal.console.Printers$D6loop$1L13munit.PrinterL20scala.runtime.IntRefL38scala.collection.mutable.StringBuilderiL16java.lang.ObjectiuEPT32munit.internal.console.Printers$
[error]   - from M32munit.internal.console.Printers$D5printL16java.lang.ObjectL13munit.PrinterL16java.lang.StringEO
[error]   - from M16munit.AssertionsD10munitPrintL15scala.Function0L16java.lang.StringEO
[error]   - from M14munit.FunSuiteD10munitPrintL15scala.Function0L16java.lang.StringEO
[error]   - from M16munit.AssertionsD17assert$$anonfun$1L15scala.Function0L15scala.Function0L14munit.LocationuEPT16munit.Assertions
[error]   - from M26munit.Assertions$$Lambda$1D12apply$mcV$spuEO
[error]   - from M16munit.AssertionsD6assertL15scala.Function0L15scala.Function0L14munit.LocationuEO
[error]   - from M14munit.FunSuiteD6assertL15scala.Function0L15scala.Function0L14munit.LocationuEO
...

This points to the code here: https://github.com/scalameta/munit/blob/main/munit/shared/src/main/scala-3/munit/internal/Compat.scala

This minimal code reproduces the error:

import scala.reflect.Selectable.reflectiveSelectable


object Main {
  def collectionClassName(i: Iterable[_]): String =
    i.asInstanceOf[{ def collectionClassName: String }].collectionClassName

  def main(args: Array[String]): Unit =                                                                                                                                  
    println(collectionClassName(Seq(1,2,3)))
}

[info] compiling 1 Scala source to /home/claudio/github/sn2-3/scala-native-seed-project/target/scala-3.1.1/classes ...
[info] Linking (2401 ms)
[error] missing symbols:
[error] * M15java.lang.ClassD8getFieldL16java.lang.StringL23java.lang.reflect.FieldEO
[error]   - from M24scala.reflect.SelectableD13selectDynamicL16java.lang.StringL16java.lang.ObjectEO
[error]   - from M42scala.reflect.Selectable$DefaultSelectableD13selectDynamicL16java.lang.StringL16java.lang.ObjectEO
[error]   - from M25scala.reflect.Selectable$D20reflectiveSelectableL16java.lang.ObjectL24scala.reflect.SelectableEO
[error]   - from M5Main$D19collectionClassNameL25scala.collection.IterableL16java.lang.StringEO
[error]   - from M5Main$D4mainLAL16java.lang.String_uEO
[error]   - from M4MainD4mainLAL16java.lang.String_uEo
[error] * M15java.lang.ClassD9getMethodL16java.lang.StringLAL15java.lang.Class_L24java.lang.reflect.MethodEO
[error]   - from M24scala.reflect.SelectableD12applyDynamicL16java.lang.StringL30scala.collection.immutable.SeqL30scala.collection.immutable.SeqL16java.lang.ObjectEO
[error]   - from M42scala.reflect.Selectable$DefaultSelectableD12applyDynamicL16java.lang.StringL30scala.collection.immutable.SeqL30scala.collection.immutable.SeqL16java.lang.ObjectEO
[error]   - from M24scala.reflect.SelectableD13selectDynamicL16java.lang.StringL16java.lang.ObjectEO
[error]   - from M42scala.reflect.Selectable$DefaultSelectableD13selectDynamicL16java.lang.StringL16java.lang.ObjectEO
[error]   - from M25scala.reflect.Selectable$D20reflectiveSelectableL16java.lang.ObjectL24scala.reflect.SelectableEO
[error]   - from M5Main$D19collectionClassNameL25scala.collection.IterableL16java.lang.StringEO
[error]   - from M5Main$D4mainLAL16java.lang.String_uEO
[error]   - from M4MainD4mainLAL16java.lang.String_uEo
[error] unable to link
[error] (Compile / nativeLink) unable to link

I assume this is something currently not supported by scala-native for Scala 3... ?!

[WojciechMazur]

Looks like this type of operation needs some special handling, I was not aware of that. I've now seen that in Scala.js they do have some special handling for selectable. We'll fix it for the next release