Crash with Match Types and unapplySeq

[SimonGuilloud]

Compiler version

3.5.1, 3.5.2, 3.6.1

Minimized code

object Test {

  sealed trait T
  sealed trait Arrow[A, B]

  type ArgsTo[S1, Target] <: NonEmptyTuple = S1 match {
    case Arrow[a, Target] => Tuple1[Expr[a]]
    case Arrow[a, b] => Expr[a] *: ArgsTo[b, Target]
  }

  sealed trait Expr[S] :
    def unapplySeq[Target](e: Expr[Target]): Option[ArgsTo[S, Target]] = ???

  case class Variable[S](id: String) extends Expr[S]

  val v = Variable[Arrow[T, Arrow[T, T]]]("v")
  val e : Expr[T] = ???

  e match
    case v[T](l, r) => ()  //This line causes the crash
    case _ => ()
}

Output (click arrow to expand)

unhandled exception while running MegaPhase{protectedAccessors, extmethods, uncacheGivenAliases, checkStatic, elimByName, hoistSuperArgs, forwardDepChecks, specializeApplyMethods, tryCatchPatterns, patternMatcher} on Test.scala

  An unhandled exception was thrown in the compiler.
  Please file a crash report here:
  https://github.com/scala/scala3/issues/new/choose
  For non-enriched exceptions, compile with -Xno-enrich-error-messages.

     while compiling: Test.scala
        during phase: MegaPhase{protectedAccessors, extmethods, uncacheGivenAliases, checkStatic, elimByName, hoistSuperArgs, forwardDepChecks, specializeApplyMethods, tryCatchPatterns, patternMatcher}
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.14
    compiler version: version 3.5.1
            settings: 

Exception in thread "main" java.util.NoSuchElementException: last of empty list
	at scala.collection.immutable.Nil$.last(List.scala:666)
	at scala.collection.immutable.Nil$.last(List.scala:662)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.unapplyProductSeqPlan$1(PatternMatcher.scala:336)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.$anonfun$12(PatternMatcher.scala:397)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.letAbstract(PatternMatcher.scala:129)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.unapplyPlan$1$$anonfun$1(PatternMatcher.scala:394)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.letAbstract(PatternMatcher.scala:129)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.unapplyPlan$1(PatternMatcher.scala:372)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.patternPlan(PatternMatcher.scala:445)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.caseDefPlan(PatternMatcher.scala:481)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.matchPlan$$anonfun$1$$anonfun$1(PatternMatcher.scala:488)
	at scala.collection.immutable.List.foldRight(List.scala:353)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.matchPlan$$anonfun$1(PatternMatcher.scala:487)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.letAbstract(PatternMatcher.scala:129)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.matchPlan(PatternMatcher.scala:485)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.translateMatch(PatternMatcher.scala:1073)
	at dotty.tools.dotc.transform.PatternMatcher.transformMatch(PatternMatcher.scala:54)
	at dotty.tools.dotc.transform.MegaPhase.goMatch(MegaPhase.scala:816)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:383)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.loop$1(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:376)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:272)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
	at dotty.tools.dotc.transform.MegaPhase.loop$1(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.mapPackage$1(MegaPhase.scala:396)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:399)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.transformUnit(MegaPhase.scala:481)
	at dotty.tools.dotc.transform.MegaPhase.run(MegaPhase.scala:493)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:380)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:334)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:373)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:343)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:336)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:384)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:396)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:396)
	at dotty.tools.dotc.Run.compileSources(Run.scala:282)
	at dotty.tools.dotc.Run.compile(Run.scala:267)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
	at dotty.tools.dotc.Driver.process(Driver.scala:201)
	at dotty.tools.dotc.Driver.process(Driver.scala:169)
	at dotty.tools.dotc.Driver.process(Driver.scala:181)
	at dotty.tools.dotc.Driver.main(Driver.scala:211)
	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:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at coursier.bootstrap.launcher.a.a(Unknown Source)
	at coursier.bootstrap.launcher.Launcher.main(Unknown Source)

More Infos

I know that I some point in my project, that was working as expected, and the type of l and r was correctly inferred (Expr[T]). However it seems I can't reliably reproduce a non-crashing behaviour, even from a fresh checkout of my project at a point where I remember it to be non-crashing. Maybe the presence of cached files or something was different and relevant.

[SimonGuilloud]

The similar but slightly different version:

  val v = Variable[Arrow[T, T]]("v")
  val e : Expr[T] = ???

  e match
    case v[T](l) => ()
    case _ => ()

produces instead the very different error:

undefined: x8.<none> # -1: TermRef(TermRef(NoPrefix,val x8),<none>) at preRecheck
1 error found

[Gedochao]

This doesn't crash for Scala 3.4.3, instead producing an error.

scala-cli compile repro.scala -S 3.4.3
# Compiling project (Scala 3.4.3, JVM (17))
# [error] ./repro.scala:20:10
# [error] Wrong number of argument patterns for Test.v[Test.T]; expected: (Test.Expr[Test.T])
# [error]     case v[T](l, r) => ()  //This line causes the crash
# [error]          ^^^^^^^^^^
# Error compiling project (Scala 3.4.3, JVM (17))

Last good stable version: 3.4.3
First bad stable version: 3.5.0