calling methods with default arguments on anonymous instances crashes the compiler

[rmgk]

Compiler version

3.1.2, 3.2.0-RC1-bin-20220527-001bfc3-NIGHTLY

Minimized code

class A:
  def f(x: Int = 1): Int = x

@main def run() =
  (new A{}).f()

Output (click arrow to expand)

abbreviated output:

exception occurred while compiling maintest.scala
java.util.NoSuchElementException: None.get while compiling maintest.scala
Exception in thread "main" java.util.NoSuchElementException: None.get
	at scala.None$.get(Option.scala:627)
	at scala.None$.get(Option.scala:626)
	at dotty.tools.dotc.transform.LambdaLift.transformTemplate(LambdaLift.scala:348)

exception occurred while compiling maintest.scala
java.util.NoSuchElementException: None.get while compiling maintest.scala
Exception in thread "main" java.util.NoSuchElementException: None.get
	at scala.None$.get(Option.scala:627)
	at scala.None$.get(Option.scala:626)
	at dotty.tools.dotc.transform.LambdaLift.transformTemplate(LambdaLift.scala:348)
	at dotty.tools.dotc.transform.LambdaLift.transformTemplate(LambdaLift.scala:344)
	at dotty.tools.dotc.transform.MegaPhase.goTemplate(MegaPhase.scala:1004)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:363)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:256)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:427)
	at dotty.tools.dotc.transform.MegaPhase.transformStat$1(MegaPhase.scala:437)
	at dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:299)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:228)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:427)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:279)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
	at dotty.tools.dotc.transform.MegaPhase.recur$2(MegaPhase.scala:453)
	at dotty.tools.dotc.transform.MegaPhase.transformTrees(MegaPhase.scala:453)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:280)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:300)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
	at dotty.tools.dotc.transform.MegaPhase.mapDefDef$1(MegaPhase.scala:249)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:252)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:427)
	at dotty.tools.dotc.transform.MegaPhase.transformStat$1(MegaPhase.scala:437)
	at dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:362)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:256)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:427)
	at dotty.tools.dotc.transform.MegaPhase.transformStat$1(MegaPhase.scala:437)
	at dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.recur$1(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:442)
	at dotty.tools.dotc.transform.MegaPhase.mapPackage$1(MegaPhase.scala:382)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:385)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:429)
	at dotty.tools.dotc.transform.MegaPhase.transformUnit(MegaPhase.scala:448)
	at dotty.tools.dotc.transform.MegaPhase.run(MegaPhase.scala:460)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:308)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:309)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:259)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1328)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:270)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:278)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:68)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:287)
	at dotty.tools.dotc.Run.compileSources(Run.scala:220)
	at dotty.tools.dotc.Run.compile(Run.scala:204)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
	at dotty.tools.dotc.Driver.process(Driver.scala:199)
	at dotty.tools.dotc.Driver.process(Driver.scala:167)
	at dotty.tools.dotc.Driver.process(Driver.scala:179)
	at dotty.tools.dotc.Driver.main(Driver.scala:209)
	at dotty.tools.dotc.Main.main(Main.scala)

[odersky]

Code after typer:

  class A() extends Object() {
    def f(x: Int): Int = x
    def f$default$1: Int @uncheckedVariance = 1
  }
  final lazy module val test$package: test$package = new test$package()
  final module class test$package() extends Object() { 
    this: test$package.type =>
    @main def run(): Int = 
      {
        final class $anon() extends A() {}
        (new $anon():A)
      }.f(
        {
          final class $anon() extends A() {}
          (new $anon():A)
        }.f$default$1
      )
  }

[nicolasstucki]

Similarly,

class A:
  def f(x: Int = 1): Int = x

def test() = (new A).f()

produces

// Scala 3
    def test(): Int = new A().f(new A().f$default$1)

I would assume the the prefix should be evaluated once. At least Scala 2 does evaluate the prefix once.

// Scala 2
    def test(): Int = {
      <artifact> val qual$1: Playground.A = new Playground.this.A();
      <artifact> val x$1: Int = qual$1.f$default$1;
      qual$1.f(x$1)
    }

[nicolasstucki]

It does lift the expression if the prefix is a def

class A:
  def f(x: Int = 1): Int = x

def makeA =
    println("Make A")
    new A

def test() = makeA.f()

produces

  def test(): Int =
    val $1$: A = makeA
    $1$.f($1$.f$default$1)  

We are probably not detecting side effects correctly with the constructors. Seems to be related with pure initializers.