REPL regression with instantiating class instances from the scala.concurrent.duration package

[ghost]

Compiler version

3.2.1

Minimized code

Open a Scala 3.2.1 REPL:

Welcome to Scala 3.2.1 (17.0.5, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                        
scala> new scala.concurrent.duration.DurationInt(5)

Output

Exception in thread "main" java.lang.ClassNotFoundException: package$DurationInt
	at dotty.tools.repl.AbstractFileClassLoader.findClass(AbstractFileClassLoader.scala:51)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:587)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
	at dotty.tools.repl.AbstractFileClassLoader.loadClass(AbstractFileClassLoader.scala:57)
	at java.base/java.lang.Class.forName0(Native Method)
	at java.base/java.lang.Class.forName(Class.java:467)
	at dotty.tools.repl.Rendering.rewrapValueClass(Rendering.scala:127)
	at dotty.tools.repl.Rendering.$anonfun$4(Rendering.scala:106)
	at scala.Option.flatMap(Option.scala:283)
	at dotty.tools.repl.Rendering.valueOf(Rendering.scala:106)
	at dotty.tools.repl.Rendering.renderVal(Rendering.scala:149)
	at dotty.tools.repl.ReplDriver.$anonfun$7(ReplDriver.scala:365)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.repl.ReplDriver.extractAndFormatMembers$1(ReplDriver.scala:371)
	at dotty.tools.repl.ReplDriver.renderDefinitions$$anonfun$2(ReplDriver.scala:403)
	at scala.Option.map(Option.scala:242)
	at dotty.tools.repl.ReplDriver.renderDefinitions(ReplDriver.scala:409)
	at dotty.tools.repl.ReplDriver.compile$$anonfun$2(ReplDriver.scala:307)
	at scala.util.Either.fold(Either.scala:189)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:323)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:248)
	at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:168)
	at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:171)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:191)
	at dotty.tools.repl.ReplDriver.runBody$$anonfun$1(ReplDriver.scala:179)
	at dotty.tools.runner.ScalaClassLoader$.asContext(ScalaClassLoader.scala:80)
	at dotty.tools.repl.ReplDriver.runBody(ReplDriver.scala:179)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:171)
	at dotty.tools.repl.ReplDriver.tryRunning(ReplDriver.scala:133)
	at dotty.tools.repl.Main$.main(Main.scala:7)
	at dotty.tools.MainGenericRunner$.run$1(MainGenericRunner.scala:193)
	at dotty.tools.MainGenericRunner$.process(MainGenericRunner.scala:270)
	at dotty.tools.MainGenericRunner$.main(MainGenericRunner.scala:281)
	at dotty.tools.MainGenericRunner.main(MainGenericRunner.scala)

Same error happens if new is not used.

Expectation

Scala 3.2.0 REPL:

Welcome to Scala 3.2.0 (17.0.5, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                        
scala> new scala.concurrent.duration.DurationInt(5)

Output:

val res0: scala.concurrent.duration.package.DurationInt = 5

Although, the result is also weird, there's a mention of scala.concurrent.duration.package.DurationInt, which is not the same fully qualified name. As far as I can tell, this behavior is consistent in Scala 3.1.3 too. I did not check older versions.

Edit:

Scala 2.13.10 reports the same value as:

val res0: concurrent.duration.DurationInt = scala.concurrent.duration.package$DurationInt@5

The mention of package might just be down to the bytecode encoding and might be completely fine.

[SethTisue]

Note that the problem isn't in the instantiation itself:

scala> (new scala.concurrent.duration.DurationInt(5)): Any
val res0: Any = scala.concurrent.duration.package$DurationInt@5

but in the REPL code for type-driven printing of values (as obvious anyway in the stack trace: dotty.tools.repl.Rendering).

It seems from #16387 that the package-object angle isn't relevant; it's a value-class thing. But maybe it's relevant that neither value-class is top level.

Dale has a suspect: #15545 . But it does have a test of an inner value class, so why are these failure cases different?

[SethTisue]

Ah, it's because you need a package declaration; it needn't be an inner class.

I think this is the minimal reproducer:

package p
class D(val n: Int) extends AnyVal

and then in the REPL, new p.D(5) or even just null.asInstanceOf[p.D]

(We should still also include a test that has an inner class and a package, though, since we're slinging JVM-level class names and inner classes is an easy area for that to go wrong.)