Crash on new line after extension def without result type or RHS

[prolativ]

Compiler version

3.2.0, 3.3.0, 3.3.2-RC1-bin-20230720-98b452d-NIGHTLY
Used not to crash in 3.1.0

Minimized code

trait Foo

val foo = new Foo:
  extension (s: String)
    def twice

(Note the empty line at the end)

Output (click arrow to expand)

-- [E019] Syntax Error: /Users/mpalka/Projects/besom/Crash.scala:5:13 ----------
5 |    def twice
  |             ^
  |             Missing return type
  |
  | longer explanation available when compiling with `-explain`
error while checking  extends Foo {
  extension (s: String) def twice = null
}
error while checking new Foo {
  extension (s: String) def twice = null
}
error while checking val foo =
  new Foo {
    extension (s: String) def twice = null
  }
error while checking package <empty> {
  trait Foo {}
  val foo =
    new Foo {
      extension (s: String) def twice = null
    }
}
exception occurred while parser /Users/mpalka/Projects/besom/Crash.scala
exception occurred while compiling /Users/mpalka/Projects/besom/Crash.scala
java.lang.AssertionError: assertion failed: position error, parent span does not contain child span
parent      =  extends Foo {
  extension (s: String) def twice = null
} # -1,
parent span = <21..67>,
child       = extension (s: String) def twice = null # -1,
child span  = [32..68] while compiling /Users/mpalka/Projects/besom/Crash.scala
Exception in thread "main" java.lang.AssertionError: assertion failed: position error, parent span does not contain child span
parent      =  extends Foo {
  extension (s: String) def twice = null
} # -1,
parent span = <21..67>,
child       = extension (s: String) def twice = null # -1,
child span  = [32..68]
        at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
        at dotty.tools.dotc.ast.Positioned.check$1(Positioned.scala:175)
        at dotty.tools.dotc.ast.Positioned.check$1$$anonfun$3(Positioned.scala:205)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.ast.Positioned.check$1(Positioned.scala:205)
        at dotty.tools.dotc.ast.Positioned.checkPos(Positioned.scala:226)
        at dotty.tools.dotc.ast.Positioned.check$1(Positioned.scala:200)
        at dotty.tools.dotc.ast.Positioned.checkPos(Positioned.scala:226)
        at dotty.tools.dotc.ast.Positioned.check$1(Positioned.scala:200)
        at dotty.tools.dotc.ast.Positioned.checkPos(Positioned.scala:226)
        at dotty.tools.dotc.ast.Positioned.check$1(Positioned.scala:200)
        at dotty.tools.dotc.ast.Positioned.check$1$$anonfun$3(Positioned.scala:205)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.ast.Positioned.check$1(Positioned.scala:205)
        at dotty.tools.dotc.ast.Positioned.checkPos(Positioned.scala:226)
        at dotty.tools.dotc.parsing.Parser.parse$$anonfun$1(ParserPhase.scala:38)
        at dotty.tools.dotc.parsing.Parser.parse$$anonfun$adapted$1(ParserPhase.scala:39)
        at scala.Function0.apply$mcV$sp(Function0.scala:42)
        at dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:437)
        at dotty.tools.dotc.parsing.Parser.parse(ParserPhase.scala:39)
        at dotty.tools.dotc.parsing.Parser.runOn$$anonfun$1(ParserPhase.scala:48)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.parsing.Parser.runOn(ParserPhase.scala:48)
        at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:247)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1321)
        at dotty.tools.dotc.Run.runPhases$1(Run.scala:263)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:271)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:280)
        at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
        at dotty.tools.dotc.Run.compileUnits(Run.scala:280)
        at dotty.tools.dotc.Run.compileSources(Run.scala:195)
        at dotty.tools.dotc.Run.compile(Run.scala:179)
        at dotty.tools.dotc.Driver.doCompile(Driver.scala:35)
        at dotty.tools.dotc.Driver.process(Driver.scala:195)
        at dotty.tools.dotc.Driver.process(Driver.scala:163)
        at dotty.tools.dotc.Driver.process(Driver.scala:175)
        at dotty.tools.dotc.Driver.main(Driver.scala:205)
        at dotty.tools.dotc.Main.main(Main.scala)

Expectations

The compilation should fail but without a crash. Note that there's no crash if the empty line gets removed from the end of the file.

[scala-center-bot]

This issue was picked for the Issue Spree No. 35 of 22 August 2023 which takes place in 7 days. @jan-pieter, @hamzaremmal, @XLPI will be working on it. If you have any insight into the issue or guidance on how to fix it, please leave it here.

[FlorianCassayre]

Here is another minimized program that appear to trigger the same issue:

given A with
  def a

Doesn't matter whether A is defined or not; the compiler should not crash in either case.

(again, notice the trailing line!)