Call to abstract inline method not failing compilation when inlined

[kubukoz]

Compiler version

3.0.0

Minimized code

trait Noop[T]:
  //note: making this "not inline" fixes the result
  inline def noop(fa: T): T

object Noop {
  inline def noop[T](alg: T)(using n: Noop[T]): T = n.noop(alg)
}

import Noop.*

final case class User(name: String, age: Int)

inline given Noop[User] = a => a

val u = User("hello", 45)

@main
def run = println(Noop.noop(u))

Output

null

Expectation

User("hello", 45)

Here's a scastie:

https://scastie.scala-lang.org/i1aeCpLuTNatjchMPW9dfQ

[bishabosha]

it appears that after inlining phase run looks like this, and prints the empty tree

class example$package$() extends Object() { this: example$package.type =>
    private def writeReplace(): AnyRef = 
      new scala.runtime.ModuleSerializationProxy(classOf[example$package.type])
    final inline given def given_Noop_User: Noop[User] = 
      {
        def $anonfun(a: User): User = a
        closure($anonfun:Noop[User])
      }:Noop[User]
    val u: User = User.apply("hello", 45)
    @main() def run: Unit = println(<empty> :User:User) // print the empty tree
  }

[OlivierBlanvillain]

Here is a slightly minimized version:

trait Noop {
  inline def noop(fa: String): String
}

class Bar extends Noop {
  inline def noop(fa: String): String = fa
}

object Test {
  val xs: Noop = new Bar
  val u: String = "hello"

  inline def boom(alg: String, n: Noop): String = n.noop(alg)

  def main(args: Array[String]): Unit =
    u.toString == boom(u, xs).toString || ???
}

I think there is something wrong with this check:

https://github.com/lampepfl/dotty/blob/a956774180d124adc98527863b919c35d5f9db92/compiler/src/dotty/tools/dotc/typer/Typer.scala#L3492-L3493

If we try to call xs.noop(u) directly, or make boom non inline, the compiler complains: Deferred inline method noop in trait Noop cannot be invoked, but that checked is missed with the boom indirection.

[nicolasstucki]

Minimized to

trait Noop {
  inline def noop: String
}

inline def boom: String = (??? : Noop).noop
def test: Unit = boom

If should have an error when inlining boom.