regression: Integer overflow in nesting level of a Macro expansion (PolyType/TypeBounds) between 3.1.1 and 3.1.2

[arixmkii]

Compiler version

3.1.2

Minimized code

It requires some macro magic to reproduce and I didn't manage to extract the minimal reproducible code. But it manifests with one specific open source project https://github.com/davenverse/epimetheus

If you perform git clone and then run sbt (in my case JDK 17 was used) with these commands it will encounter compilation errors.

++ 3.1.2; Test / compile

Output

sbt log

[error] -- Error: ~/epimetheus/core/src/test/scala/io/chrisdavenport/epimetheus/CounterSpec.scala:30:68 
[error] 30 |        counter <- Counter.labelled(cr, Name("boo"), "Boo Counter", Sized(Label("foo")), {(s: String) => Sized(s)})
[error]    |                                                                    ^
[error]    |Could not decrease the nesting level of a from 2147483647 to 6 in

And a lot more of PolyType and TypeBounds output.

Expectation

Compile w/o errors like it was with 3.1.1

++ 3.1.1; Test / compile

[soronpo]

Please try and provide a minimized example. It's less likely the issue will be resolved if the error is not minimized (someone has to do it, and the compiler geniuses are busy doing the real work 😉).

[arixmkii]

I managed to minimize it to 2 Scala sources (because Macros support is involved) - Base - with macro definitions and Test with failing example. It is still big, but I eliminated all external dependencies at least.

Base.scala

package testcase

import scala.compiletime.ops.int.*

final class Label (val getLabel: String)

trait ShapelessPolyfill {

  type Represented[R] = R match {
    case IndexedSeq[a] => a
  }

  type TupleSized[R, A, N <: Int] <: Tuple = N match {
    case 0 => EmptyTuple
    case S[n] => A *: TupleSized[R, A, n]
  }

  extension [R, A, N <: Int] (s: TupleSized[R, A, N]) {
    def unsized: IndexedSeq[A] = s.productIterator.toIndexedSeq.asInstanceOf[IndexedSeq[A]]
  }

  type Nat = Int

  type Sized[Repr, L <: Nat] = TupleSized[Repr, Represented[Repr], L]

  object Sized {
    def apply[A](a1: A): Sized[IndexedSeq[A], 1] = Tuple1(a1)
  }

}

object poly extends ShapelessPolyfill

Test.scala

package testcase

import poly.*

def failing: Tuple1[Label] = Sized(new Label("foo"))

With 3.1.1 it compiles

nestingbug % ls -a                 
.		..		Base.scala	Test.scala
nestingbug % scalac -version       
Scala compiler version 3.1.1 -- Copyright 2002-2022, LAMP/EPFL
nestingbug % scalac Base.scala     
nestingbug % scalac Test.scala

With 3.1.2 it fails

nestingbug % ls -a
.		..		Base.scala	Test.scala
nestingbug % scalac -version
Scala compiler version 3.1.2 -- Copyright 2002-2022, LAMP/EPFL
nestingbug % scalac Base.scala
nestingbug % scalac Test.scala
-- Error: Test.scala:5:29 ------------------------------------------------------
5 |def failing: Tuple1[Label] = Sized(Label("foo"))
  |                             ^
  |Could not decrease the nesting level of a from 2147483647 to 2 in 
... A lot more output omitted...

[arixmkii]

Edited previous reply to minimize it more.

[arixmkii]

Updated once again. This is now the most minimal what I can provide.