NullPointerException was delayed throw

[Glavo]

For the following code, it can run normally:

object Main {
  val a = null.asInstanceOf[Nothing]
  def main(args: Array[String]): Unit = {
  }
}

But NullPointerException will only be thrown when using a:

object Main {
  val a = null.asInstanceOf[Nothing]
  def main(args: Array[String]): Unit = {
    a
  }
}

sbt:dotty-simple> run
[info] Compiling 1 Scala source to /home/glavo/IdeaProjects/dotty/test/target/scala-0.8/classes ...
[info] Done compiling.
[info] Packaging /home/glavo/IdeaProjects/dotty/test/target/scala-0.8/dotty-simple_0.8-0.1.0.jar ...
[info] Done packaging.
[info] Running Main 
[error] (run-main-6) java.lang.NullPointerException
[error] java.lang.NullPointerException
[error] 	at Main$.a(Main.scala:2)
[error] 	at Main$.main(Main.scala:4)
[error] 	at Main.main(Main.scala)
[error] 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[error] 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[error] 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[error] 	at java.lang.reflect.Method.invoke(Method.java:498)
[error] 	at sbt.Run.invokeMain(Run.scala:93)
[error] 	at sbt.Run.run0(Run.scala:87)
[error] 	at sbt.Run.execute$1(Run.scala:65)
[error] 	at sbt.Run.$anonfun$run$4(Run.scala:77)
[error] 	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error] 	at sbt.util.InterfaceUtil$$anon$1.get(InterfaceUtil.scala:10)
[error] 	at sbt.TrapExit$App.run(TrapExit.scala:252)
[error] 	at java.lang.Thread.run(Thread.java:748)
[error] java.lang.RuntimeException: Nonzero exit code: 1
[error] 	at sbt.Run$.executeTrapExit(Run.scala:124)
[error] 	at sbt.Run.run(Run.scala:77)
[error] 	at sbt.Defaults$.$anonfun$bgRunTask$5(Defaults.scala:1172)
[error] 	at sbt.Defaults$.$anonfun$bgRunTask$5$adapted(Defaults.scala:1167)
[error] 	at sbt.internal.BackgroundThreadPool.$anonfun$run$1(DefaultBackgroundJobService.scala:366)
[error] 	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
[error] 	at scala.util.Try$.apply(Try.scala:209)
[error] 	at sbt.internal.BackgroundThreadPool$BackgroundRunnable.run(DefaultBackgroundJobService.scala:289)
[error] 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
[error] 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
[error] 	at java.lang.Thread.run(Thread.java:748)
[error] (Compile / run) Nonzero exit code: 1
[error] Total time: 1 s, completed 2018-4-29 12:40:42

I think NullPointerException or ClassCastException should be thrown when the conversion happens

[Glavo]

Also, NullPointerException was thrown when I tried to convert null to Nothing in REPL:

scala> val a = (null.asInstanceOf[Nothing]: Null) 
java.lang.NullPointerException
	at rs$line$1$.<init>(rs$line$1:1)
	at rs$line$1$.<clinit>(rs$line$1)
	at rs$line$1.aShow(rs$line$1)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at dotty.tools.repl.Rendering.valueOf(Rendering.scala:58)
	at dotty.tools.repl.Rendering.renderVal(Rendering.scala:79)
	at dotty.tools.repl.ReplDriver.displayMembers$3$$anonfun$3(ReplDriver.scala:284)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
	at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:52)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
	at scala.collection.TraversableLike.map(TraversableLike.scala:234)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
	at scala.collection.AbstractTraversable.map(Traversable.scala:104)
	at dotty.tools.repl.ReplDriver.displayMembers$7(ReplDriver.scala:284)
	at dotty.tools.repl.ReplDriver.displayDefinitions$$anonfun$3$$anonfun$2(ReplDriver.scala:311)
	at scala.Option.map(Option.scala:146)
	at dotty.tools.repl.ReplDriver.displayDefinitions$$anonfun$1(ReplDriver.scala:311)
	at dotty.tools.dotc.core.Periods.atPhase(Periods.scala:26)
	at dotty.tools.dotc.core.Phases.atPhase(Phases.scala:36)
	at dotty.tools.repl.ReplDriver.displayDefinitions(ReplDriver.scala:316)
	at dotty.tools.repl.ReplDriver.compile$$anonfun$2(ReplDriver.scala:241)
	at scala.util.Either.fold(Either.scala:188)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:242)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:202)
	at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:150)
	at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:154)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput$$anonfun$2$$anonfun$1(ReplDriver.scala:163)
	at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
	at scala.Console$.withErr(Console.scala:192)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput$$anonfun$1(ReplDriver.scala:163)
	at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
	at scala.Console$.withOut(Console.scala:163)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:163)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:154)
	at dotty.tools.repl.Main$.main(Main.scala:6)
	at dotty.tools.repl.Main.main(Main.scala)

But a is still defined and NoClassDefFoundError is thrown when use it:

scala> a 
java.lang.NoClassDefFoundError: Could not initialize class rs$line$1$
	at rs$line$2$.<init>(rs$line$2:1)
	at rs$line$2$.<clinit>(rs$line$2)
	at rs$line$2.res0Show(rs$line$2)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at dotty.tools.repl.Rendering.valueOf(Rendering.scala:58)
	at dotty.tools.repl.Rendering.renderVal(Rendering.scala:79)
	at dotty.tools.repl.ReplDriver.displayMembers$3$$anonfun$3(ReplDriver.scala:284)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
	at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:52)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
	at scala.collection.TraversableLike.map(TraversableLike.scala:234)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
	at scala.collection.AbstractTraversable.map(Traversable.scala:104)
	at dotty.tools.repl.ReplDriver.displayMembers$7(ReplDriver.scala:284)
	at dotty.tools.repl.ReplDriver.displayDefinitions$$anonfun$3$$anonfun$2(ReplDriver.scala:311)
	at scala.Option.map(Option.scala:146)
	at dotty.tools.repl.ReplDriver.displayDefinitions$$anonfun$1(ReplDriver.scala:311)
	at dotty.tools.dotc.core.Periods.atPhase(Periods.scala:26)
	at dotty.tools.dotc.core.Phases.atPhase(Phases.scala:36)
	at dotty.tools.repl.ReplDriver.displayDefinitions(ReplDriver.scala:316)
	at dotty.tools.repl.ReplDriver.compile$$anonfun$2(ReplDriver.scala:241)
	at scala.util.Either.fold(Either.scala:188)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:242)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:202)
	at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:150)
	at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:154)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput$$anonfun$2$$anonfun$1(ReplDriver.scala:163)
	at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
	at scala.Console$.withErr(Console.scala:192)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput$$anonfun$1(ReplDriver.scala:163)
	at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)
	at scala.Console$.withOut(Console.scala:163)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:163)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:154)
	at dotty.tools.repl.Main$.main(Main.scala:6)
	at dotty.tools.repl.Main.main(Main.scala)

This behavior is beyond my expectation!

[Glavo]

When I use ClassVIewer to view this bytecode, I find that when the conversion value is Nothing, it's just cast to scala.runtime.Nothing$:

I think there is also a need to insert a null-detecting code to prevent the type system from being destroyed.

[smarter]

Duplicate of #3340