Crash while declaring a new anonymous subtype with extra paren

[romaincomeau]

Compiler version

compiler version: version 3.3.1

Minimized code

Notice the extra parenthese in
def combine(x: Int, y: Int))

trait Monoid[A]:
  def combine(x: A, y: A): A
  def empty: A

object Monoid:
  lazy val addInt: Monoid[Int] = new:
    val empty = 0
    def combine(x: Int, y: Int)) = x + y

Output (click arrow to expand)

romaincomeau@phoenix monoids % scalac /tmp/extra_paren.scala
-- [E019] Syntax Error: /tmp/extra_paren.scala:8:31 ----------------------------
8 |    def combine(x: Int, y: Int)) = x + y
  |                               ^
  |                               Missing return type
  |
  | longer explanation available when compiling with `-explain`
error while checking  {
  val empty = 0
  def combine(x: Int, y: Int) = null
}
error while checking new  {
  val empty = 0
  def combine(x: Int, y: Int) = null
}
error while checking lazy val addInt: Monoid[Int] =
  new  {
    val empty = 0
    def combine(x: Int, y: Int) = null
  }
error while checking  {
  lazy val addInt: Monoid[Int] =
    new  {
      val empty = 0
      def combine(x: Int, y: Int) = null
    }
}
error while checking module object Monoid {
  lazy val addInt: Monoid[Int] =
    new  {
      val empty = 0
      def combine(x: Int, y: Int) = null
    }
}
error while checking package <empty> {
  trait Monoid[A] {
    def combine(x: A, y: A): A
    def empty: A
  }
  module object Monoid {
    lazy val addInt: Monoid[Int] =
      new  {
        val empty = 0
        def combine(x: Int, y: Int) = null
      }
  }
}
exception occurred while parser /tmp/extra_paren.scala

  exception occurred while compiling List(/tmp/extra_paren.scala)

  An unhandled exception was thrown in the compiler.
  Please file a crash report here:
  https://github.com/lampepfl/dotty/issues/new/choose

     while compiling: <no file>
        during phase: <no phase>
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.10
    compiler version: version 3.3.1
            settings:

                tree: EmptyTree
       tree position: :<unknown>
           tree type: <notype>
              symbol: val <none>
           call site: package <root> in module class <root>

  == Source file context for tree position ==


Exception in thread "main" java.lang.AssertionError: assertion failed: position error, parent span does not contain child span
parent      =  {
  val empty = 0
  def combine(x: Int, y: Int) = null
} # -1,
parent span = <110..173>,
child       = def combine(x: Int, y: Int) = null # -1,
child span  = [137..141..175]
	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.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$$anonfun$adapted$1(ParserPhase.scala:39)
	at scala.Function0.apply$mcV$sp(Function0.scala:42)
	at dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:440)
	at dotty.tools.dotc.parsing.Parser.parse(ParserPhase.scala:39)
	at dotty.tools.dotc.parsing.Parser.runOn$$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$$anonfun$1(Run.scala:246)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1321)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:262)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:270)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:279)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:279)
	at dotty.tools.dotc.Run.compileSources(Run.scala:194)
	at dotty.tools.dotc.Run.compile(Run.scala:179)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
	at dotty.tools.dotc.Driver.process(Driver.scala:197)
	at dotty.tools.dotc.Driver.process(Driver.scala:165)
	at dotty.tools.dotc.Driver.process(Driver.scala:177)
	at dotty.tools.dotc.Driver.main(Driver.scala:207)
	at dotty.tools.MainGenericCompiler$.run$1(MainGenericCompiler.scala:162)
	at dotty.tools.MainGenericCompiler$.main(MainGenericCompiler.scala:186)
	at dotty.tools.MainGenericCompiler.main(MainGenericCompiler.scala)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at coursier.bootstrap.launcher.a.a(Unknown Source)
	at coursier.bootstrap.launcher.Launcher.main(Unknown Source)

[i10416]

It seems similar to #18265 fixed by #18743. Did you try compiling it with nightly?

I tried with the current master branch and it won't crash.