scalac GC error with LocalDateTime, Generic and Selector

[qwe2]

I have a strange error with Generic and Select on a case class containing LocalDateTime. I haven't been able to pinpoint the issue exactly, but having both in my case class causes very high compilation times in my project. Example code:

  case class WAT(
    ld: java.time.LocalDate,
    a: String,
    b: String,
    ldt: java.time.LocalDateTime
  )

  def x[H <: HList, T](
    implicit
    gen: Generic.Aux[WAT, H],
    at: Selector[H, LocalDateTime]
  ): Nothing = ???

x

This is the minimal failing example I could come up with. This causes scalac to go on for what seems to be forever (haven't finished in ~1 hour), with a lot of GC activity and 1GB of heap space. If I increase the number of fields it will eventually fail with the below error. If I remove a: String or b: String from the case class, the compilation still takes a bit longer than usual (ie, if I do Selector[H, String] the compilation time is noticeably quicker), but it still compiles. Is this an issue with shapeless or am I doing something else wrong that I don't quite see?

Error:scalac: Error: GC overhead limit exceeded
java.lang.OutOfMemoryError: GC overhead limit exceeded
	at scala.reflect.internal.Types$Type.scala$reflect$internal$Types$Type$$findMemberInternal$1(Types.scala:1019)
	at scala.reflect.internal.Types$Type.findMember(Types.scala:1021)
	at scala.reflect.internal.Types$Type.memberBasedOnName(Types.scala:636)
	at scala.reflect.internal.Types$Type.nonPrivateMember(Types.scala:612)
	at scala.reflect.internal.Types$class.rebind(Types.scala:3422)
	at scala.reflect.internal.Types$class.typeRef(Types.scala:3497)
	at scala.reflect.internal.SymbolTable.typeRef(SymbolTable.scala:16)
	at scala.reflect.internal.Symbols$TypeSymbol.newTypeRef(Symbols.scala:3081)
	at scala.reflect.internal.Symbols$TypeSymbol.typeConstructor(Symbols.scala:3103)
	at scala.reflect.internal.Symbols$TypeSymbol.tpeHK(Symbols.scala:3106)
	at scala.reflect.internal.Types$TypeVar$.createTypeVar(Types.scala:2833)
	at scala.reflect.internal.Types$TypeVar$.apply(Types.scala:2806)
	at scala.reflect.internal.Types$ExistentialType$$anonfun$23.apply(Types.scala:2701)
	at scala.reflect.internal.Types$ExistentialType$$anonfun$23.apply(Types.scala:2701)
	at scala.collection.immutable.List.map(List.scala:284)

Scala version: 2.11.11 Shapeless version: 2.3.2

Please note that these are the latest versions I'm able to use due to some restrictions on the project.

[joroKr21]

F-bounded types strike again?

scala> List("", LocalDate.now(), LocalDateTime.now())
res1: List[Comparable[_ >: java.time.chrono.ChronoLocalDateTime[?0] with java.time.chrono.ChronoLocalDate with String forSome { type ?0 } <: Comparable[_ >: java.time.chrono.ChronoLocalDateTime[?0] with java.time.chrono.ChronoLocalDate with String forSome { type ?0 } <: Comparable[_ >: java.time.chrono.ChronoLocalDateTime[?0] with java.time.chrono.ChronoLocalDate with String forSome { type ?0 } <: Object] forSome { type ?0 }] forSome { type ?0 }] with java.io.Serializable] = List("", 2018-03-19, 2018-03-19T22:25:44.370)

[qwe2]

I'm not familiar enough with the internals of shapeless to know why this would cause an issue in a case class. The only workaround I found so far is to wrap each such type individually like so:

case class LocalDateWrapper(value: LocalDate)
case class LocalDateTimeWrapper(value: LocalDateTime)

[joroKr21]

I'm not 100% sure myself, so take with a grain of salt, but my reasoning goes like this

The issue is not with shapeless itself, but with subtyping tests taking forever on F-bounded types to a large depth. The depth depends on the complexity of the type and HLists are obviously complex types. The subtyping tests involved are just part of the standard implicit resolution in Scala, no macro magic involved here (take a look at the definition of Selector).