Unable to call recursive private inline method defined in a trait

[julienrf]

Compiler version

3.0.0

Minimized code

package bugreport

import scala.compiletime.erasedValue

object Obj:
  
  inline def length[Tuple]: Int = loop[Tuple]

  private inline def loop[Tuple]: Int =
    inline erasedValue[Tuple] match
      case _: EmptyTuple => 0
      case _: (head *: tail) => 1 + loop[tail]

end Obj

// Same code, but in a trait instead of an object
trait Trait:

  inline def length[Tuple]: Int = loop[Tuple]

  private inline final def loop[Tuple]: Int =
    inline erasedValue[Tuple] match
      case _: EmptyTuple => 0
      case _: (head *: tail) => 1 + loop[tail]

end Trait

@main def run() =
  println(Obj.length[(Int, Int, String)]) // OK
  new Trait:
    println(length[(Int, Int, String)]) // ERROR

Output

[error] -- Error: bugreport.scala:18:38 
[error] 18 |  inline def length[Tuple]: Int = loop[Tuple]
[error]    |                                  ^^^^^^^^^^^
[error]    |undefined: Trait_this.loop # -1: TermRef(TermRef(NoPrefix,val Trait_this),loop) at inlining

When I call the variant in the trait, I get this error. But the same code works fine with an object.

Expectation

Both versions work.

[heksesang]

Should you be able to inline a method at a call site which shouldn't be accessible at that call site? If not, the problem here is that the object version in fact works.

[odersky]

In fact, it seems the version with an object does not work either. I get:

-- Error: i11706.scala:83:2 ----------------------------------------------------
83 |  Obj.caseClass[Foo]
   |  ^^^^^^^^^^^^^^^^^^
   |object creation impossible, since def show(a: A): String in trait Show in package bugreport is not defined 
   |(Note that
   | parameter A in def show(a: A): String in trait Show in package bugreport does not match
   | parameter String *: scala.Tuple$package.EmptyTuple.type in def show(tuple: String *: scala.Tuple$package.EmptyTuple.type): String in anonymous class Object with bugreport.Show[head *: tail] {...}
   | )
   | This location contains code that was inlined from i11706.scala:72
   | This location contains code that was inlined from i11706.scala:70
   | This location contains code that was inlined from i11706.scala:57
1 error found

[julienrf]

@odersky That error is a bit confusing.

I managed to reproduce and minimize further the error I originally reported: it happens only when we call a private recursive inline method. I have updated the issue description accordingly.