Anonymous functions direct application crash the compiler.

[nicolasstucki]

object Foo {
  (new Function0[Unit] {
    def apply() = println("hello")
  })()
}

Note that this does not fail if the apply method is written explicitly.

Exception in thread "main" java.lang.Error: unexpected type.
 fun = Block(List(TypeDef($anon,Template(DefDef(<init>,List(),List(List()),TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,scala)),Unit)],EmptyTree),List(Apply(Select(New(TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,lang)),Object)]),<init>),List()), AppliedTypeTree(Ident(Function0),List(Ident(Unit)))),ValDef(_,EmptyTree,EmptyTree),List(DefDef(apply,List(),List(List()),TypeTree[TypeRef(ThisType(TypeRef(NoPrefix,$anon)),scala$Function0$$R)],Apply(Ident(println),List(Literal(Constant(hello))))))))),Typed(Select(Apply(Select(New(Ident($anon)),<init>),List()),apply),TypeTree[MethodType(List(), List(), TypeRef(TermRef(ThisType(TypeRef(NoPrefix,<root>)),scala),Unit))])),
 methPart(fun) = Typed(Select(Apply(Select(New(Ident($anon)),<init>),List()),apply),TypeTree[MethodType(List(), List(), TypeRef(TermRef(ThisType(TypeRef(NoPrefix,<root>)),scala),Unit))]),
 methPart(fun).tpe = MethodType(List(), List(), TypeRef(TermRef(ThisType(TypeRef(NoPrefix,<root>)),scala),Unit)),
 tpe = MethodType(List(), List(), TypeRef(TermRef(ThisType(TypeRef(NoPrefix,<root>)),scala),Unit))
    at dotty.tools.dotc.typer.Applications$class.handleUnexpectedFunType(Applications.scala:661)
    at dotty.tools.dotc.typer.Typer.handleUnexpectedFunType(Typer.scala:60)
    at dotty.tools.dotc.typer.Applications$$anonfun$realApply$1$1.dotty$tools$dotc$typer$Applications$class$$anonfun$$simpleApply$1(Applications.scala:577)
    at dotty.tools.dotc.typer.Applications$$anonfun$realApply$1$1$$anonfun$apply$5.apply(Applications.scala:603)
    at dotty.tools.dotc.typer.Applications$$anonfun$realApply$1$1$$anonfun$apply$5.apply(Applications.scala:603)
    at dotty.tools.dotc.typer.Typer.tryEither(Typer.scala:1472)
    at dotty.tools.dotc.typer.Applications$$anonfun$realApply$1$1.apply(Applications.scala:604)
    at dotty.tools.dotc.typer.Applications$$anonfun$realApply$1$1.apply(Applications.scala:544)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:36)
    at dotty.tools.dotc.typer.Applications$class.realApply$1(Applications.scala:544)
    at dotty.tools.dotc.typer.Applications$class.typedApply(Applications.scala:647)
    at dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:60)
    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1376)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1417)
    at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1427)
    at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1425)
    at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:155)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:56)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1425)
    at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:1455)
    at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1460)
    at dotty.tools.dotc.typer.Typer$$anonfun$typedClassDef$1.apply(Typer.scala:1196)
    at dotty.tools.dotc.typer.Typer$$anonfun$typedClassDef$1.apply(Typer.scala:1144)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:36)
    at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:1144)
    at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1367)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1415)
    at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1427)
    at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1425)
    at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:155)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:56)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1425)
    at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:1449)
    at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1460)
    at dotty.tools.dotc.typer.Typer$$anonfun$typedPackageDef$1.apply(Typer.scala:1292)
    at dotty.tools.dotc.typer.Typer$$anonfun$typedPackageDef$1.apply(Typer.scala:1283)
    at dotty.tools.dotc.util.Stats$.track(Stats.scala:36)
    at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:1283)
    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1405)
    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1417)
    at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1427)
    at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1425)
    at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:155)
    at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:56)
    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1425)
    at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1464)
    at dotty.tools.dotc.typer.FrontEnd$$anonfun$typeCheck$1.apply$mcV$sp(FrontEnd.scala:47)
    at dotty.tools.dotc.typer.FrontEnd.monitor(FrontEnd.scala:23)
    at dotty.tools.dotc.typer.FrontEnd.typeCheck(FrontEnd.scala:45)
    at dotty.tools.dotc.typer.FrontEnd$$anonfun$runOn$3.apply(FrontEnd.scala:69)
    at dotty.tools.dotc.typer.FrontEnd$$anonfun$runOn$3.apply(FrontEnd.scala:69)
    at scala.collection.immutable.List.foreach(List.scala:381)
    at dotty.tools.dotc.typer.FrontEnd.runOn(FrontEnd.scala:69)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1$$anonfun$apply$mcV$sp$1.apply(Run.scala:69)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1$$anonfun$apply$mcV$sp$1.apply(Run.scala:66)
    at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)
    at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1.apply$mcV$sp(Run.scala:66)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1.apply(Run.scala:60)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1.apply(Run.scala:60)
    at dotty.tools.dotc.util.Stats$.monitorHeartBeat(Stats.scala:69)
    at dotty.tools.dotc.Run.compileUnits(Run.scala:60)
    at dotty.tools.dotc.Run.compileSources(Run.scala:57)
    at dotty.tools.dotc.Run.compile(Run.scala:41)
    at dotty.tools.dotc.Driver.doCompile(Driver.scala:26)
    at dotty.tools.dotc.Driver.process(Driver.scala:124)
    at dotty.tools.dotc.Driver.process(Driver.scala:93)
    at dotty.tools.dotc.Driver.process(Driver.scala:105)
    at dotty.tools.dotc.Driver.main(Driver.scala:132)
    at dotty.tools.dotc.Main.main(Main.scala)

[felixmulder]

Leaving these notes here for tomorrow. Basically when typing:

(new Function0[Unit] {
  def apply() = println("...")
})()

The typedApply function receives a block in fun1:

val fun1 = typedExpr(tree.fun, originalProto)

That has the type MethodType instead of a TermRef (extracted via methPart(fun1)). We could patch this by creating a block with a val which rhs is the tree.fun and then applying it with tree.args - but we're unsure why the block original block in fun1 gets a MethodType instead of a TermRef

[felixmulder]

In Typer.scala#ensureNoLocalRefs we ascribe a type while avoiding localSyms. This is where the MethodType comes from - is this ascribing the wrong type?

[odersky]

I would compare with

({() => println("hello")})() 

1. In Printers, turn typr printer on.
2. Run compilation with -Ylog:front and pipe the result into a file
3. Do the same with the Function0 code.
4. Diff the two logs. That will show where we go wrong with the Function0 code.