Crash at pickling when summon ClassTag for union of nested arrays

[bishabosha]

Compiler version

3.0.1

Minimized code

val foo = reflect.classTag[Array[Array[Int]] | Array[Array[Int]]]

Output (click arrow to expand)

Crash is caused by a missing case of JavaArrayType in the TreePickler

scala.MatchError: JavaArrayType(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Int)) (of class dotty.tools.dotc.core.Types$CachedJavaArrayType) while compiling sem/foo.scala
Exception in thread "main" scala.MatchError: JavaArrayType(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Int)) (of class dotty.tools.dotc.core.Types$CachedJavaArrayType)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType(TreePickler.scala:302)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleType(TreePickler.scala:171)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType$$anonfun$11$$anonfun$1(TreePickler.scala:192)
	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.core.tasty.TreePickler.pickleNewType$$anonfun$2(TreePickler.scala:192)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:69)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType(TreePickler.scala:192)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleType(TreePickler.scala:171)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleConstant(TreePickler.scala:153)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:454)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$38$$anonfun$1(TreePickler.scala:439)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$3(TreePickler.scala:439)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:69)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:440)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$38$$anonfun$1(TreePickler.scala:439)
	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.core.tasty.TreePickler.pickleTree$$anonfun$3(TreePickler.scala:439)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:69)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:440)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTreeUnlessEmpty(TreePickler.scala:330)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$1(TreePickler.scala:345)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:69)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:347)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:556)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:371)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleStats(TreePickler.scala:371)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$26(TreePickler.scala:597)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:69)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:598)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$1(TreePickler.scala:342)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:69)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:347)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:573)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:371)
	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.core.tasty.TreePickler.pickleStats(TreePickler.scala:371)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$29(TreePickler.scala:613)
	at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:69)
	at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:613)
	at dotty.tools.dotc.core.tasty.TreePickler.pickle$$anonfun$1(TreePickler.scala:784)
	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.core.tasty.TreePickler.pickle(TreePickler.scala:784)
	at dotty.tools.dotc.transform.Pickler.run$$anonfun$3$$anonfun$2(Pickler.scala:69)
	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.transform.Pickler.run$$anonfun$1(Pickler.scala:106)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.transform.Pickler.run(Pickler.scala:106)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:303)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:304)
	at dotty.tools.dotc.transform.Pickler.runOn(Pickler.scala:111)
	at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:205)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$5(Run.scala:216)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:224)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:231)
	at dotty.tools.dotc.Run.compileSources(Run.scala:166)
	at dotty.tools.dotc.Run.compile(Run.scala:150)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
	at dotty.tools.dotc.Driver.process(Driver.scala:199)
	at dotty.tools.dotc.Driver.process(Driver.scala:167)
	at dotty.tools.dotc.Driver.process(Driver.scala:179)
	at dotty.tools.dotc.Driver.main(Driver.scala:209)
	at dotty.tools.dotc.Main.main(Main.scala)

[smarter]

Crash is caused by a missing case of JavaArrayType in the TreePickler

I don't think JavaArrayType should reach TreePickler, i think the issue is that https://github.com/lampepfl/dotty/blob/ec15557c1bcce768c1cc8c59b7bc4cb6e8d5e9dc/compiler/src/dotty/tools/dotc/typer/Synthesizer.scala#L42-L44 should recursively replace JavaArrayType by ArrayOf in elemType

[griggt]

See also #11043 (same stack trace)

[bishabosha]

palindrome issue