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Generic tuple in unapplySeq crash #25663

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Generic tuple in unapplySeq crash#25663
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itype:bugitype:crashstat:needs triageEvery issue needs to have an "area" and "itype" label
@eejbyfeldt

Description

@eejbyfeldt
eejbyfeldt
opened on Mar 31, 2026

Compiler version

3.7.4, 3.8.4-RC1-bin-20260331-724e9c3-NIGHTLY

Minimized code

object Foo:
  def unapplySeq(f: Int): Option[String *: Seq[Int] *: EmptyTuple] = ???

def foo(f: Int) = f match
  case Foo(name, ns*) => ???

Output (click arrow to expand)

Details 
$ scala-cli -S 3.nightly unapplySeq_crash.scala Compiling project (Scala 3.8.4-RC1-bin-20260331-724e9c3-NIGHTLY, JVM (21))
Error compiling project (Scala 3.8.4-RC1-bin-20260331-724e9c3-NIGHTLY, JVM (21))
Error: java.util.NoSuchElementException: last of empty list
        at scala.collection.immutable.Nil$.last(List.scala:663)
	at scala.collection.immutable.Nil$.last(List.scala:663)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.unapplyProductSeqPlan$1(PatternMatcher.scala:367)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.$anonfun$12(PatternMatcher.scala:434)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.letAbstract(PatternMatcher.scala:123)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.unapplyPlan$1$$anonfun$1(PatternMatcher.scala:431)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.letAbstract(PatternMatcher.scala:123)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.unapplyPlan$1(PatternMatcher.scala:409)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.patternPlan(PatternMatcher.scala:494)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.caseDefPlan(PatternMatcher.scala:540)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.matchPlan$$anonfun$1$$anonfun$1(PatternMatcher.scala:554)
	at scala.collection.immutable.List.foldRight(List.scala:346)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.matchPlan$$anonfun$1(PatternMatcher.scala:553)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.letAbstract(PatternMatcher.scala:123)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.matchPlan(PatternMatcher.scala:551)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.translateMatch(PatternMatcher.scala:1139)
	at dotty.tools.dotc.transform.PatternMatcher.transformMatch(PatternMatcher.scala:53)
	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.mapDefDef$1(MegaPhase.scala:265)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:268)
	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.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$$anonfun$1(Phases.scala:411)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:327)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:403)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:380)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1324)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:373)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$2(Run.scala:420)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$adapted$1(Run.scala:420)
	at scala.Function0.apply$mcV$sp(Function0.scala:42)
	at dotty.tools.dotc.Run.showProgress(Run.scala:482)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:420)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:432)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:432)
	at dotty.tools.dotc.Run.compileSources(Run.scala:319)
	at dotty.tools.dotc.Run.compile(Run.scala:304)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
	at dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:141)
	at dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.compileSources$1(BloopHighLevelCompiler.scala:148)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.$anonfun$compile$9(BloopHighLevelCompiler.scala:181)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.$anonfun$compile$1(BloopHighLevelCompiler.scala:73)
	at bloop.tracing.NoopTracer$.trace(BraveTracer.scala:53)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.timed$1(BloopHighLevelCompiler.scala:72)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.$anonfun$compile$8(BloopHighLevelCompiler.scala:181)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
	at monix.eval.internal.TaskRunLoop$.startFull(TaskRunLoop.scala:81)
	at monix.eval.internal.TaskRestartCallback.syncOnSuccess(TaskRestartCallback.scala:101)
	at monix.eval.internal.TaskRestartCallback.onSuccess(TaskRestartCallback.scala:74)
	at monix.eval.internal.TaskExecuteOn$AsyncRegister$$anon$1.run(TaskExecuteOn.scala:71)
	at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1423)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188)

Error: Unexpected error when compiling scala_playground_535bbcb374-67da7489ad: java.util.NoSuchElementException: last of empty list
	at scala.collection.immutable.Nil$.last(List.scala:663)
	at scala.collection.immutable.Nil$.last(List.scala:663)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.unapplyProductSeqPlan$1(PatternMatcher.scala:367)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.$anonfun$12(PatternMatcher.scala:434)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.letAbstract(PatternMatcher.scala:123)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.unapplyPlan$1$$anonfun$1(PatternMatcher.scala:431)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.letAbstract(PatternMatcher.scala:123)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.unapplyPlan$1(PatternMatcher.scala:409)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.patternPlan(PatternMatcher.scala:494)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.caseDefPlan(PatternMatcher.scala:540)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.matchPlan$$anonfun$1$$anonfun$1(PatternMatcher.scala:554)
	at scala.collection.immutable.List.foldRight(List.scala:346)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.matchPlan$$anonfun$1(PatternMatcher.scala:553)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.letAbstract(PatternMatcher.scala:123)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.matchPlan(PatternMatcher.scala:551)
	at dotty.tools.dotc.transform.PatternMatcher$Translator.translateMatch(PatternMatcher.scala:1139)
	at dotty.tools.dotc.transform.PatternMatcher.transformMatch(PatternMatcher.scala:53)
	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.mapDefDef$1(MegaPhase.scala:265)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:268)
	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.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$$anonfun$1(Phases.scala:411)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:327)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:403)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:380)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1324)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:373)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$2(Run.scala:420)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$adapted$1(Run.scala:420)
	at scala.Function0.apply$mcV$sp(Function0.scala:42)
	at dotty.tools.dotc.Run.showProgress(Run.scala:482)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:420)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:432)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:432)
	at dotty.tools.dotc.Run.compileSources(Run.scala:319)
	at dotty.tools.dotc.Run.compile(Run.scala:304)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
	at dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:141)
	at dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.compileSources$1(BloopHighLevelCompiler.scala:148)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.$anonfun$compile$9(BloopHighLevelCompiler.scala:181)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.$anonfun$compile$1(BloopHighLevelCompiler.scala:73)
	at bloop.tracing.NoopTracer$.trace(BraveTracer.scala:53)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.timed$1(BloopHighLevelCompiler.scala:72)
	at sbt.internal.inc.bloop.internal.BloopHighLevelCompiler.$anonfun$compile$8(BloopHighLevelCompiler.scala:181)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
	at monix.eval.internal.TaskRunLoop$.startFull(TaskRunLoop.scala:81)
	at monix.eval.internal.TaskRestartCallback.syncOnSuccess(TaskRestartCallback.scala:101)
	at monix.eval.internal.TaskRestartCallback.onSuccess(TaskRestartCallback.scala:74)
	at monix.eval.internal.TaskExecuteOn$AsyncRegister$$anon$1.run(TaskExecuteOn.scala:71)
	at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1423)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188)

Compilation failed

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