scala-js file order sensitive bug related to https://github.com/scala/scala/pull/7966?

[adriaanm]

to reproduce, checkout branch t11525 from https://github.com/adriaanm/scala-js

sbt javalanglib/compile:

> javalanglib/compile
[info] Compiling 42 Scala sources to /Users/adriaan/git/scala-js/javalanglib/target/scala-2.13.0-pre-2ef2f9f/classes...
ArrayBuffer(/Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Long.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Math.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/InheritableThreadLocal.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Appendable.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Comparable.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/StringBuffer.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/StackTraceElement.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Runtime.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/ThreadLocal.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Character.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Void.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Cloneable.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/StackTrace.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Number.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Thread.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Readable.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Integer.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/StringBuilder.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/AutoCloseable.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/System.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/ClassLoader.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Byte.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Class.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Throwables.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/FloatingPointBits.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Double.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/ObjectClone.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/CharSequence.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Iterable.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/_String.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Short.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Enum.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Runnable.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Boolean.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Float.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/ref/PhantomReference.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/ref/Reference.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/ref/SoftReference.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/ref/ReferenceQueue.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/ref/WeakReference.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/reflect/Array.scala, /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/annotation/Annotation.scala)
[error] /Users/adriaan/git/scala-js/javalanglib/src/main/scala/java/lang/Iterable.scala:18: error: type arguments [T] do not conform to trait Iterator's type parameter bounds [E <: Object]
[error]   def iterator(): Iterator[T]
[error]                   ^
[info] one error found

[adriaanm]

This one was tricky. File order in adriaanm/scala-js@9bb932c was discovered on CI (linux machine, also Eugene's dbuild box), whereas our macs compiled the project ok.

[adriaanm]

self-contained repro:

package java.lang

import java.util.Iterator

class Class[A](o: Object)

class Comparable[A] { def compareTo(o: A): scala.Int = ??? }

object System {
  def currentTimeMillis(): scala.Long = ???

  def arraycopy(src: Object, srcPos: scala.Int, dest: Object, destPos: scala.Int, length: scala.Int): Unit = {
    import scala.{Boolean, Double}

    def mismatch(): Nothing =
      throw new ArrayStoreException("Incompatible array types")

    def copyPrim[@specialized T](src: Array[T], dest: Array[T]): Unit = {
        var i = length-1
        while (i >= 0) {
          dest(i+destPos) = src(i+srcPos)
          i -= 1
        }
    }

    def copyRef(src: Array[AnyRef], dest: Array[AnyRef]): Unit = {
      val x = (src.length, dest.length)
      
      var i = length-1
      while (i >= 0) {
        dest(i+destPos) = src(i+srcPos)
        i -= 1
      }
    }

    (src match {
      case src: Array[Boolean] =>
        dest match {
          case dest: Array[Boolean] => copyPrim(src, dest)
          case _                    => mismatch()
        }

    })
  }

  def identityHashCode(x: Object): scala.Int = {
    x.getClass
    1
  }
}

trait Iterable[T] {
  def iterator():  java.util.Iterator[T]
}

Repro's pretty consistently with:

 scalac /tmp/iter.scala -Ystop-after:refchecks -verbose -Ydebug -uniqid

🤷‍♂

[adriaanm]

compiling this yields the same error:

error: type arguments [T] do not conform to trait Iterator's type parameter bounds [E <: Object]
  def iterator(): Iterator[T]
                  ^
one error found

[adriaanm]

I spent a lot of time trying to prune the repro, but this seems as small as I could get it.

Just compiling this with -uniqid makes the error go away (sometimes). WTF

[adriaanm]

Ok, I think I figured it out. ObjectTpeJava is still replaced by ObjectTpe when uniqueing a Type that contains ObjectTpeJava, since e.g. TypeBounds(...ObjectTpeJava...).equalsTypeBounds(...ObjectTpe...) and thus uniqueing the TypeBounds will also replace our precious ObjectTpeJava by ObjectTpe.