Cannot emit primitive conversion from Lscala/runtime/Null$; to I

[sir-wabbit]

scala> def foo(b: Null with Nothing): Int = b
java.lang.AssertionError: assertion failed: 
  Cannot emit primitive conversion from Lscala/runtime/Null$; to I - <console>
     while compiling: <console>
        during phase: jvm
     library version: version 2.13.0-M3
    compiler version: version 2.13.0-M3
  reconstructed args: -deprecation -classpath /home/alex/.ivy2/cache/org.scala-lang/scala-compiler/jars/scala-compiler-2.13.0-M3.jar:/home/alex/.ivy2/cache/org.scala-lang/scala-reflect/jars/scala-reflect-2.13.0-M3.jar:/home/alex/.ivy2/cache/org.scala-lang.modules/scala-xml_2.13.0-M3/bundles/scala-xml_2.13.0-M3-1.0.6.jar:/home/alex/.ivy2/cache/jline/jline/jars/jline-2.14.5.jar -Yrepl-sync -bootclasspath /usr/lib/jvm/java-8-oracle/jre/lib/resources.jar:/usr/lib/jvm/java-8-oracle/jre/lib/rt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/sunrsasign.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jsse.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jce.jar:/usr/lib/jvm/java-8-oracle/jre/lib/charsets.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jfr.jar:/usr/lib/jvm/java-8-oracle/jre/classes:/home/alex/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.13.0-M3.jar

  last tree to typer: Ident(b)
       tree position: line 1 of <console>
            tree tpe: Null
              symbol: value b
   symbol definition: b: Null (a TermSymbol)
      symbol package: $line85
       symbol owners: value b -> method foo -> object iw
           call site: constructor $read$$iw$$iw in package $line85

<Cannot read source file>
	at scala.tools.nsc.backend.jvm.BCodeIdiomatic$JCodeMethodN.emitT2T(BCodeIdiomatic.scala:225)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.adapt(BCodeBodyBuilder.scala:829)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:389)
	at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.emitNormalMethodBody$1(BCodeSkelBuilder.scala:604)
	at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genDefDef(BCodeSkelBuilder.scala:636)
	at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:510)
	at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.$anonfun$gen$7(BCodeSkelBuilder.scala:512)
	at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:512)
	at scala.tools.nsc.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:112)
	at scala.tools.nsc.backend.jvm.CodeGen.genClass(CodeGen.scala:52)
	at scala.tools.nsc.backend.jvm.CodeGen.genClassDef$1(CodeGen.scala:24)
	at scala.tools.nsc.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:40)
	at scala.tools.nsc.backend.jvm.CodeGen.$anonfun$genUnit$2(CodeGen.scala:39)
	at scala.tools.nsc.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:39)
	at scala.tools.nsc.backend.jvm.CodeGen.genUnit(CodeGen.scala:43)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.$anonfun$apply$1(GenBCode.scala:43)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.apply(GenBCode.scala:43)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$applyPhase$1(Global.scala:436)
	at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:429)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1(Global.scala:400)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1$adapted(Global.scala:400)
	at scala.collection.Iterator.foreach(Iterator.scala:938)
	at scala.collection.Iterator.foreach$(Iterator.scala:938)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1426)
	at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:400)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.super$run(GenBCode.scala:53)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.$anonfun$run$1(GenBCode.scala:53)
	at scala.tools.nsc.backend.jvm.GenBCode$BCodePhase.run(GenBCode.scala:51)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1453)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1437)
	at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compile(IMain.scala:711)
	at scala.tools.nsc.interpreter.IMain$Request.compile(IMain.scala:900)
	at scala.tools.nsc.interpreter.IMain.$anonfun$compile$2(IMain.scala:504)
	at scala.tools.nsc.interpreter.IMain.compile(IMain.scala:504)
	at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:498)
	at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:481)
	at scala.tools.nsc.interpreter.shell.ILoop.interpretStartingWith(ILoop.scala:892)
	at scala.tools.nsc.interpreter.shell.ILoop.command(ILoop.scala:750)
	at scala.tools.nsc.interpreter.shell.ILoop.processLine(ILoop.scala:455)
	at scala.tools.nsc.interpreter.shell.ILoop.loop(ILoop.scala:478)
	at scala.tools.nsc.interpreter.shell.ILoop.$anonfun$run$1(ILoop.scala:985)
	at scala.tools.nsc.interpreter.shell.ILoop.run(ILoop.scala:950)
	at scala.tools.nsc.InterpreterLoop.main(Interpreter.scala:71)
	at xsbt.ConsoleInterface.run(ConsoleInterface.scala:62)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:101)
	at sbt.compiler.AnalyzingCompiler.console(AnalyzingCompiler.scala:76)
	at sbt.Console.sbt$Console$$console0$1(Console.scala:22)
	at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply$mcV$sp(Console.scala:23)
	at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply(Console.scala:23)
	at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply(Console.scala:23)
	at sbt.Logger$$anon$4.apply(Logger.scala:85)
	at sbt.TrapExit$App.run(TrapExit.scala:248)
	at java.lang.Thread.run(Thread.java:748)

[sir-wabbit]

Also found the following inconsistency:

scala> def foo(b: Null with Int): Int = b
java.lang.AssertionError: assertion failed: 
  Cannot emit primitive conversion from Lscala/runtime/Null$; to I - <console>
....

scala> def foo(b: Null with Long): Int = b
foo: (b: Null with Long)Int

[He-Pin]

in Scala 2.12.4 too

[OndrejSpanel]

What does this error mean? I am hitting it now in a large project with lots of implicit conversion (a DSL, not a normal Scala code).

In my case the issue was one function declared to return Int was returning null in one path. The errors were not much helpful, they seemed to be triggered on a place where there is apparently no Null or null.

[SethTisue]

@OndrejSpanel I'm not sure we can offer further insight unless you have a standalone reproducer that's interestingly different from the ones we already have in this ticket

[SethTisue]

in 2.13.3, you instead get:

scala 2.13.3> def foo(b: Null with Nothing): Int = b
java.lang.VerifyError: Bad type on operand stack
Exception Details:
  Location:
    foo(Lscala/runtime/Null$;)I @3: ireturn
  Reason:
    Type null (current frame, stack[0]) is not assignable to integer
  Current Frame:
    bci: @3
    flags: { }
    locals: { '$iw', 'scala/runtime/Null$' }
    stack: { null }
  Bytecode:
    0x0000000: 2b57 01ac

  ... 31 elided

🤷

[dwijnand]

Need to send a JEP to add 🤷 before java.lang.VerifyError