given instance is declared as erased, but is in fact used

[ghostdogpr]

Compiler version

3.0.1

Minimized code

import scala.deriving.Mirror
import scala.compiletime._

trait Schema[T] {
  def build: T
}

object Schema extends SchemaDerivation {
  implicit lazy val int: Schema[Int]   = ???
  implicit def option[A](implicit ev: Schema[A]): Schema[Option[A]] = ???
}

trait SchemaDerivation {
  inline def recurse[A <: Tuple]: List[Schema[Any]] =
    inline erasedValue[A] match {
      case _: (t *: ts) =>
        val builder = summonInline[Schema[t]].asInstanceOf[Schema[Any]]
        builder :: recurse[ts]
      case _: EmptyTuple => Nil
    }

  inline def derived[A]: Schema[A] =
    inline summonInline[Mirror.Of[A]] match {
      case m: Mirror.SumOf[A] =>
        lazy val subTypes = recurse[m.MirroredElemTypes]
        new Schema[A] {
          def build: A = ???
        }

      case m: Mirror.ProductOf[A] =>
        lazy val fields = recurse[m.MirroredElemTypes]
        new Schema[A] {
          def build: A = ???
        }
    }

  inline given gen[A]: Schema[A] = derived
}

case class H(i: Int)
case class G(h: H)
case class F(g: G)
case class E(f: Option[F])
case class D(e: E)
case class C(d: D)
case class B(c: C)
case class A(a: Option[A], b: B)

object TestApp {
  @main def test = {
    implicit lazy val typeSchema: Schema[A] = Schema.gen
  }
}

Output

given instance gen is declared as erased, but is in fact used
method recurse is declared as erased, but is in fact used

Expectation

I got this error while upgrading caliban from 3.0.0 to 3.0.1 on some code that was previously compiling. It seems that it fails to derive a typeclass instance in the presence of recursion and nesting. If I reduce the nesting, it works. I managed to reproduce it with the smaller example above, but this code fails with 3.0.0 with a different error. Any idea what's going on?

[griggt]

FWIW, the example compiles for me on both 3.0.0 and 3.0.1 with -Xmax-inlines 33 (the default is 32)

[ghostdogpr]

FWIW, the example compiles for me on both 3.0.0 and 3.0.1 with -Xmax-inlines 33 (the default is 32)

Oh, I was not aware of this setting, I confirm it solves my initial problem 👍
Maybe the error message could be more explicit?

[joroKr21]

Is this a new option? The same code that compiled without it on Scala 3.0.0 now requires increasing this value on Scala 3.0.1: typelevel/kittens#376 Also a bit annoying for build.sbt that we can't use -Xmax-inlines:33 or -Xmax-inlines=33 😄

[dwijnand]

Also a bit annoying for build.sbt that we can't use -Xmax-inlines:33 or -Xmax-inlines=33

Coming in 3.1.0: #13267

[nicolasstucki]

It seems we are missing not inlining one of the calls to Schema.{gen, recurse}. This then fails with an error that mentions the erased nature of inline methods. This should wither inline during the inlining phase or fail with an error at that phase. It should not reach the erasure phase.

[ghostdogpr]

I had this error come up in a new place when I upgraded from 3.0.2 to 3.1.0 (similar derivation for very nested and recursive code). Increasing -Xmax-inlines didn't solve it this time, the compilation seemed to never end.