"NoSuchElementException: key not found" with unusual partial function

[szeiger]

In 0.26.0-bin-20200718-c753ca3-NIGHTLY and 0.25.0-RC2 this crashes the compiler:

(f => scala.util.Try(f(0)) match { case v => v }): PartialFunction[Any => Any, Any]

java.util.NoSuchElementException: key not found: method $anonfun while traversing x
java.util.NoSuchElementException: key not found: method $anonfun while traversing x.apply
java.util.NoSuchElementException: key not found: method $anonfun while traversing x.apply(scala.Int.box(0))
java.util.NoSuchElementException: key not found: method $anonfun while traversing def $anonfun(): Object = x.apply(scala.Int.box(0))
java.util.NoSuchElementException: key not found: method $anonfun while traversing {
  def $anonfun(): Object = x.apply(scala.Int.box(0))
  closure($anonfun:Function0)
}
...

It works in 2.11/2.12/2.13. Minimized from this real use case: https://github.com/slick/slick/blob/eecc74fa1ba8e477e6fbd991b5b9bbb87b8f3918/slick/src/main/scala/slick/jdbc/SQLiteProfile.scala#L136-L138

[griggt]

Minimized further:

def g(x: => Any): Any = x
val a: PartialFunction[Any => Any, Any] = (f => g(f(0)) match { case v => v })

With dotty 0.27.0-RC1:

[info] Compiling 1 Scala source to /src/dotty-issues/i9391/target/scala-0.27/classes ...
java.util.NoSuchElementException: key not found: method $anonfun while traversing x
java.util.NoSuchElementException: key not found: method $anonfun while traversing x.apply
java.util.NoSuchElementException: key not found: method $anonfun while traversing x.apply(scala.Int.box(0))
java.util.NoSuchElementException: key not found: method $anonfun while traversing def $anonfun(): Object = x.apply(scala.Int.box(0))
java.util.NoSuchElementException: key not found: method $anonfun while traversing {
...

The trigger seems to be the by-name parameter to g, as this modified example illustrates:

def g(x: => Any): Any = x
def h(x: Any): Any = x

//val a: PartialFunction[Any => Any, Any] = (f => g(f(0)) match { case v => v })    // error
val a: PartialFunction[Any => Any, Any] = (f => h(f(0)) match { case v => v })      // OK

[info] Compiling 1 Scala source to /src/dotty-issues/i9391/target/scala-0.27/classes ...
[success] Total time: 2 s, completed Sep 19, 2020, 11:52:02 AM