Overrides with abstract types crash complier

[nicolasstucki]

class Test {
  type A
  def foo(): A = ???
  def foo(): A = ???
}

and

class Test {
  type A
  def foo(x: A) = ???
  def foo(x: A) = ???
}

crash the compiler in the frontend.

The second fails with:

java.lang.AssertionError: assertion failed: data race? overwriting symbol of type ((x: Test.this.A)Nothing)(Test.this.foo),
long form = TermRef(ThisType(TypeRef(ThisType(TypeRef(NoPrefix,<empty>)),Test)),foo)/withSig(Signature(List(java.lang.Object),scala.Nothing)) of class class dotty.tools.dotc.core.Types$TermRefWithSignature,
last sym id = 3316, new sym id = 3317,
last owner = class Test, new owner = class Test,
period = frontend at run 2
	at scala.Predef$.assert(Predef.scala:165)
	at dotty.tools.dotc.core.Types$NamedType.checkSymAssign(Types.scala:1508)
	at dotty.tools.dotc.core.Types$NamedType.setDenot(Types.scala:1552)
	at dotty.tools.dotc.core.Types$NamedType.withDenot(Types.scala:1545)
	at dotty.tools.dotc.core.Types$TermRef$.withSigAndDenot(Types.scala:1955)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.termRefWithSig(SymDenotations.scala:1122)
	at dotty.tools.dotc.typer.TypeAssigner$$anonfun$assignType$5.apply(TypeAssigner.scala:502)
	at dotty.tools.dotc.typer.TypeAssigner$$anonfun$assignType$5.apply(TypeAssigner.scala:502)
	at dotty.tools.dotc.core.Types$Type.orElse(Types.scala:102)
	at dotty.tools.dotc.typer.TypeAssigner$class.assignType(TypeAssigner.scala:502)
	at dotty.tools.dotc.typer.Typer.assignType(Typer.scala:65)
	at dotty.tools.dotc.typer.Typer$$anonfun$typedDefDef$1.apply(Typer.scala:1253)
	at dotty.tools.dotc.typer.Typer$$anonfun$typedDefDef$1.apply(Typer.scala:1223)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:1223)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1514)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1571)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1590)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1588)
	at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:136)
	at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:57)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1588)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:1612)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1632)
	at dotty.tools.dotc.typer.Typer$$anonfun$typedClassDef$1.apply(Typer.scala:1323)
	at dotty.tools.dotc.typer.Typer$$anonfun$typedClassDef$1.apply(Typer.scala:1271)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:1271)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1517)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1571)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1590)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1588)
	at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:136)
	at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:57)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1588)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:1612)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1632)
	at dotty.tools.dotc.typer.Typer$$anonfun$typedPackageDef$1.apply(Typer.scala:1432)
	at dotty.tools.dotc.typer.Typer$$anonfun$typedPackageDef$1.apply(Typer.scala:1419)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:1419)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1556)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1572)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1590)
	at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1588)
	at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:136)
	at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:57)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1588)
	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1644)
	at dotty.tools.dotc.typer.FrontEnd$$anonfun$typeCheck$1.apply$mcV$sp(FrontEnd.scala:64)
	at dotty.tools.dotc.typer.FrontEnd.monitor(FrontEnd.scala:32)
	at dotty.tools.dotc.typer.FrontEnd.typeCheck(FrontEnd.scala:62)
	at dotty.tools.dotc.typer.FrontEnd$$anonfun$runOn$3.apply(FrontEnd.scala:93)
	at dotty.tools.dotc.typer.FrontEnd$$anonfun$runOn$3.apply(FrontEnd.scala:93)
	at scala.collection.immutable.List.foreach(List.scala:381)
	at dotty.tools.dotc.typer.FrontEnd.runOn(FrontEnd.scala:93)

Similar stacktrace for the first.

This issue affects all override checks in #2136.

[odersky]

The crash is caused by setting -Yno-double-bindings, which is an internal consistency check. It is on by default in the test suite. However, this option triggers an exception if there are double definitions, which is what happens in the tests.

[nicolasstucki]

Indeed, removing that flag fixes the issue in #2230.
I will also create a test to check that these overload fail correctly without the -Yno-double-bindings.