crash on compilable code: at dotty.tools.dotc.util.Positions$Position$.start$extension

[helloqirun]

scalac can compile it but dotc crashes.

$ cat abc.scala

object DepBug {
  class A {
    class B
    def mkB = new B
    def m(b: B) = b
  }
  trait Dep {
    val a: A
    val b: a.B
  }
  val dep = new {
    val a = new A
    val b = a mkB
  }
  def useDep(d: Dep) {
    import d._
    a m (b)
  }
  {
    import dep._
    a m (b)
  }
  dep.a m (dep b)
}

$ dotc abc.scala

-- Error: abc.scala ----------------------------------------------------------------------------------------------------
15 |  def useDep(d: Dep) {
   |                     ^
   |                     '=' expected but '{' found
-- Error: abc.scala ----------------------------------------------------------------------------------------------------
19 |  {
   |  ^
   |  '}' expected but '{' found

exception occurred while parsing abc.scala

exception occurred while compiling abc.scala
Exception in thread "main" java.lang.AssertionError: assertion failed
	at scala.Predef$.assert(Predef.scala:151)
	at dotty.tools.dotc.util.Positions$Position$.start$extension(Positions.scala:40)
	at dotty.tools.dotc.parsing.Parsers$Parser.simpleExprRest(Parsers.scala:1199)
	at dotty.tools.dotc.parsing.Parsers$Parser.simpleExpr(Parsers.scala:1186)
	at dotty.tools.dotc.parsing.Parsers$Parser$$anonfun$8.apply(Parsers.scala:1137)
	at dotty.tools.dotc.parsing.Parsers$Parser$$anonfun$8.apply(Parsers.scala:1128)
	at dotty.tools.dotc.parsing.Parsers$Parser.postfixExpr(Parsers.scala:1124)
<snipped>

[liufengyun]

Thanks @helloqirun , report confirmed.

Here there are several problems here:

1. Compiling without -language:Scala2 would crash compiler
2. When compile with -language:Scala2, dep.a can't be resolved, where dep is the anonymous class instance.