Intellij IDEA cannot resolve symbol on implicits (scala tagless final)

Question

I have some code using tagless final approach and found that Intellij IDEA couldn't recognize method from implicit class.

I have some type-classes here (Functor, Apply, Applicative etc.) and one implicit class FunctorOps with some helper methods for Functor. This code compiles but IDEA couldn't found void and implicit Applicative. Look at the errors:

Cannot resolve symbol void:44

No implicit arguments of type: Applicative[F_]:51

The code looks not too difficult:

trait Functor[F[_]] {
  def map[A, B](fa: F[A])(ab: A => B): F[B]
}

trait Semigroupal[F[_]] {
  def product[A, B](fa: F[A], fb: F[B]): F[(A, B)]
}

trait Apply[F[_]] extends Semigroupal[F] with Functor[F] {
  def map2[A, B, Result](fa: F[A], fb: F[B])(abr: (A, B) => Result): F[Result] =
    map(product(fa, fb))(abr.tupled)
}

trait Applicative[F[_]] extends Apply[F] {
  def pure[A](a: A): F[A]
}

object Implicits {

  final implicit class FunctorOps[F[_]: Functor, A](private val fa: F[A]) {
    @inline def map[B](ab: A => B): F[B] =
      F.map(fa)(ab)

    @inline def void: F[Unit] =
      F.map(fa)(_ => ())
  }
}

trait Random[F[_]] {
  def nextInt(n: Int): F[Int]

  def void: F[Unit]
}

object Random {
  import Implicits.FunctorOps

  def dsl[F[_]: Applicative]: Random[F] =
    new Random[F] {
      override def nextInt(n: Int): F[Int] = F.pure(scala.util.Random.nextInt(n))

      override def void: F[Unit] = nextInt(4).void
    }
}

object Foo {

  def dsl[F[_]: Applicative]: F[Unit] =
    Random.dsl.void
}

My question: is there any way to avoid this errors in IDEA or it is better to use for example VS Code with Metals or something else? Is there somethign works better with tagless final?

I use std lib and add compiler plugin in sbt for using F dot method syntax:

addCompilerPlugin("org.augustjune" %% "context-applied" % "0.1.4")

Code with build parameters in scastie

screenshots:

My environment:

Intellij IDEA version 2020.2.3 (with last stable scala plugin)
OS: MacOS Catalina 10.15.7

I would just use metals with whatever editor you prefer. InteliJ is famous for its false compilation errors, and the more "advanced" or complex the code is, the more it tend to fail. — Luis Miguel Mejía Suárez
Cannot reproduce: monosnap.com/file/2msi8gcCEl8DF4kdVgfdwrwjJSTxyx Try File | Invalidate Caches/Restart.. | Invalidate and Restart. If problem remains please report at youtrack.jetbrains.com/issues/SCL with a minimal sample project. Thank you. — Andrey
@Andrey from your screenshot I got that you are using Intellij IDEA EAP (early access) version but I'm using last stable build (updated question). I downloaded this IDEA version and these wrong errors disappeared. Thank you for your try. I hope IDEA will keep correct behavior in future stable releases. — Boris Azanov

Boris Azanov Boris Azanov · Accepted Answer · 2020-11-26T07:18:21

0

votes

This behavior fixed in next stable Intellij IDEA version 2020.2.4 and works properly.

Intellij IDEA cannot resolve symbol on implicits (scala tagless final)

1 Answers