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object generation compiles successfully. #12322

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kynthus opened this issue Jan 26, 2021 · 7 comments · Fixed by scala/scala#9457
Closed

object generation compiles successfully. #12322

kynthus opened this issue Jan 26, 2021 · 7 comments · Fixed by scala/scala#9457
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@Jasper-M
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has PR regression
Milestone
2.13.5

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@kynthus
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kynthus commented Jan 26, 2021 •
edited

reproduction steps

using Scala 2.13.4,

I can compile by instantiating an object.
The following code produces a java.lang.IllegalAccessError at runtime:

// ObjectNew.scala

object MyObj {
  val a: Int = 123
  val b: Double = 456.789
  val c: String = "ABC"
}

object ObjectNew {
  def main(args: Array[String]): Unit = {
    val mo: MyObj.type = new MyObj.type() // here
  }
}
# scalac -version
Scala compiler version 2.13.4 -- Copyright 2002-2020, LAMP/EPFL and Lightbend, Inc.
# scalac ObjectNew.scala
# scala ObjectNew
Exception in thread "main" java.lang.IllegalAccessError: tried to access method MyObj$.<init>()V from class Main$
        at Main$.main(ObjectNew.scala:11)
        at Main.main(ObjectNew.scala)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at scala.reflect.internal.util.ScalaClassLoader.$anonfun$run$2(ScalaClassLoader.scala:105)
        at scala.reflect.internal.util.ScalaClassLoader.asContext(ScalaClassLoader.scala:40)
        at scala.reflect.internal.util.ScalaClassLoader.asContext$(ScalaClassLoader.scala:37)
        at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:130)
        at scala.reflect.internal.util.ScalaClassLoader.run(ScalaClassLoader.scala:105)
        at scala.reflect.internal.util.ScalaClassLoader.run$(ScalaClassLoader.scala:97)
        at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:130)
        at scala.tools.nsc.CommonRunner.run(ObjectRunner.scala:29)
        at scala.tools.nsc.CommonRunner.run$(ObjectRunner.scala:28)
        at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:43)
        at scala.tools.nsc.CommonRunner.runAndCatch(ObjectRunner.scala:35)
        at scala.tools.nsc.CommonRunner.runAndCatch$(ObjectRunner.scala:34)
        at scala.tools.nsc.AbstractScriptRunner.runCompiled(ScriptRunner.scala:168)
        at scala.tools.nsc.AbstractScriptRunner.$anonfun$runScript$1(ScriptRunner.scala:177)
        at scala.tools.nsc.AbstractScriptRunner.$anonfun$withCompiledScript$9(ScriptRunner.scala:154)
        at scala.tools.nsc.util.package$.waitingForThreads(package.scala:55)
        at scala.tools.nsc.AbstractScriptRunner.runScript(ScriptRunner.scala:151)
        at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:74)
        at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:91)
        at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:103)
        at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:108)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

In Scala 2.13.3 or older, a compile error.

[root@localhost ~]# scalac -version
Scala compiler version 2.13.3 -- Copyright 2002-2020, LAMP/EPFL and Lightbend, Inc.
[root@localhost ~]# scalac ObjectNew.scala
ObjectNew.scala:11: error: class type required but MyObj.type found
    val mo: MyObj.type = new MyObj.type()
                                  ^
1 error

problem

Unable to detect object instantiation error at compile time.
@Jasper-M
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Jasper-M commented Jan 26, 2021 •
edited

If you wrap it in a class you get an AssertionError.

class Wrapper {
  object MyObj
  val obj = new MyObj.type
}
Click for AssertionError 
java.lang.AssertionError: assertion failed: 
  transformCaseApply: name = MyObj tree = MyObj / class scala.reflect.internal.Trees$Ident
     while compiling: <pastie>
        during phase: refchecks
     library version: version 2.13.4
    compiler version: version 2.13.4

  last tree to typer: This(class Wrapper)
       tree position: line 3 of <pastie>
            tree tpe: Wrapper.this.type
              symbol: class Wrapper
   symbol definition: class Wrapper extends AnyRef (a ClassSymbol)
      symbol package: <empty>
       symbol owners: class Wrapper
           call site: object MyObj in class Wrapper in package <empty>

== Source file context for tree position ==

     1 class Wrapper {
     2   object MyObj
     3   val obj = new MyObj.type
     4 }
     5 
	at scala.reflect.internal.SymbolTable.throwAssertionError(SymbolTable.scala:170)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1786)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:81)
	at scala.reflect.internal.Trees$SingletonTypeTree.transform(Trees.scala:913)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1847)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:81)
	at scala.reflect.internal.Trees$New.transform(Trees.scala:733)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1847)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:81)
	at scala.reflect.internal.Trees$Select.transform(Trees.scala:852)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1847)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:81)
	at scala.reflect.internal.Trees$Apply.transform(Trees.scala:786)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1847)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:81)
	at scala.reflect.internal.Trees$ValDef.$anonfun$transform$4(Trees.scala:433)
	at scala.reflect.api.Trees$Transformer.atOwner(Trees.scala:2633)
	at scala.reflect.internal.Trees$ValDef.transform(Trees.scala:432)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1847)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStat(RefChecks.scala:1228)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStats(RefChecks.scala:1212)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStats(RefChecks.scala:81)
	at scala.reflect.internal.Trees$Template.transform(Trees.scala:544)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1847)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:81)
	at scala.reflect.api.Trees$Transformer.transformTemplate(Trees.scala:2595)
	at scala.reflect.internal.Trees$ClassDef.$anonfun$transform$2(Trees.scala:361)
	at scala.reflect.api.Trees$Transformer.atOwner(Trees.scala:2633)
	at scala.reflect.internal.Trees$ClassDef.transform(Trees.scala:360)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1847)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStat(RefChecks.scala:1240)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStats(RefChecks.scala:1212)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStats(RefChecks.scala:81)
	at scala.reflect.internal.Trees$PackageDef.$anonfun$transform$1(Trees.scala:342)
	at scala.reflect.api.Trees$Transformer.atOwner(Trees.scala:2633)
	at scala.reflect.internal.Trees$PackageDef.transform(Trees.scala:342)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1847)
	at scala.tools.nsc.ast.Trees$Transformer.transformUnit(Trees.scala:182)
	at scala.tools.nsc.transform.Transform$Phase.apply(Transform.scala:32)
	at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:454)
	at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:401)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1515)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1499)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1491)
	at scala.tools.nsc.interpreter.IMain.compileSourcesKeepingRun(IMain.scala:431)
	at scala.tools.nsc.interpreter.IMain.compileSources(IMain.scala:439)
	at scala.tools.nsc.interpreter.shell.ILoop$paste$.compilePaste(ILoop.scala:855)
	at scala.tools.nsc.interpreter.shell.ILoop.$anonfun$pasteCommand$13(ILoop.scala:826)
	at scala.tools.nsc.interpreter.shell.ReplReporterImpl.indenting(Reporter.scala:51)
	at scala.tools.nsc.interpreter.shell.ILoop.pasteCommand(ILoop.scala:830)
	at scala.tools.nsc.interpreter.shell.ILoop.$anonfun$standardCommands$8(ILoop.scala:201)
	at scala.tools.nsc.interpreter.shell.LoopCommands$LineCmd.apply(LoopCommands.scala:160)
	at scala.tools.nsc.interpreter.shell.LoopCommands.colonCommand(LoopCommands.scala:122)
	at scala.tools.nsc.interpreter.shell.LoopCommands.colonCommand$(LoopCommands.scala:120)
	at scala.tools.nsc.interpreter.shell.ILoop.colonCommand(ILoop.scala:45)
	at scala.tools.nsc.interpreter.shell.ILoop.command(ILoop.scala:431)
	at scala.tools.nsc.interpreter.shell.ILoop.processLine(ILoop.scala:440)
	at scala.tools.nsc.interpreter.shell.ILoop.loop(ILoop.scala:458)
	at scala.tools.nsc.interpreter.shell.ILoop.run(ILoop.scala:968)
	at xsbt.ConsoleInterface.run(ConsoleInterface.scala:78)
	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.internal.inc.AnalyzingCompiler.call(AnalyzingCompiler.scala:248)
	at sbt.internal.inc.AnalyzingCompiler.console(AnalyzingCompiler.scala:210)
	at sbt.Console.console0$1(Console.scala:48)
	at sbt.Console.$anonfun$apply$2(Console.scala:51)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
	at sbt.util.InterfaceUtil$$anon$1.get(InterfaceUtil.scala:10)
	at sbt.TrapExit$App.run(TrapExit.scala:257)
	at java.lang.Thread.run(Thread.java:748)

@dwijnand dwijnand added this to the 2.13.5 milestone Jan 26, 2021
@dwijnand
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The assertion is:

              assert(sym != NoSymbol, "transformCaseApply: name = " + name.debugString + " tree = " + tree + " / " + tree.getClass) //debug

and that output above is:

>   transformCaseApply: name = MyObj tree = MyObj / class scala.reflect.internal.Trees$Ident

@sjrd
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sjrd commented Jan 26, 2021

Could this have been caused by scala/scala#9279 ?

@Jasper-M
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@sjrd Yes, it affects this check.

@Jasper-M Jasper-M mentioned this issue Jan 26, 2021
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@Jasper-M
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Something even more ominous:

scala> object Foo
object Foo

scala> type Bar = Foo.type
type Bar

scala> val a = new Bar
val a: Foo.type = Foo$@678e08c0

scala> val b = new Bar
val b: Foo.type = Foo$@1fa8d460

scala> a == b
val res2: Boolean = false

@SethTisue
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SethTisue commented Jan 26, 2021 •
edited

@kynthus nice catch!
@Jasper-M thanks for jumping on this

@kynthus
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kynthus commented Jan 26, 2021

Everyone, Thanks.

I don't know if it's related, but it seems that it can be inherited.

scala> object Foo
object Foo

scala> type Bar = Foo.type
type Bar

scala> class Baz extends Bar
class Baz

scala> class Baz extends Foo.type // java.lang.AssertionError

I hope it will be fixed at the same time.

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Disallow new MyObj.type Jasper-M/scala
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@SethTisue @dwijnand @sjrd @Jasper-M @kynthus