Cats-tagless - Scala macro annotation error

Question

I have created a simple trait using cats-tagless lib:

@finalAlg
@autoFunctorK(true)
trait MyService[F[_]] {

  def put(element: Element): F[Element]

  def get(elementId: Id): F[Element]

  def all(): F[List[Element]]

  def delete(elementId: Id): F[Unit]
}

but when I tried to compile it, I got an error:

Error:(8, 7) macro annotation could not be expanded (the most common reason for that is that you need to enable the macro paradise plugin; another possibility is that you try to use macro annotation in the same compilation run that defines it)

I also added addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.1" cross CrossVersion.full) into plugins.sbt file and build.sbt but it did not help. Can you help me to solve it?

My build.sbt file looks like:

addCompilerPlugin(("org.scalameta" % "paradise" % "3.0.0-M11").cross(CrossVersion.full))

lazy val commonSettings = Seq(
  libraryDependencies ++= Seq(
    "org.typelevel" %% "cats-core" % CatsVersion,
    "org.typelevel" %% "cats-effect" % "1.2.0",
    "org.typelevel" %% "cats-tagless-macros" % "0.5",
    "org.typelevel" %% "cats-tagless-legacy-macros" % "0.5",
    "org.typelevel" %% "cats-mtl-core" % "0.5.0",
  )
)

Yes, I'm using it in module `algebra` where I have created service `trait`. Use it like this `lazy val algebra = (project in file("algebra")) .settings(commonSettings)` — Developus, Apr 14 '19 at 16:03

Andrey Tyukin · Accepted Answer · 2019-04-14T16:25:48.143

In an empty new project with this build.sbt:

scalaVersion := "2.12.8"

libraryDependencies ++= Seq(
  "org.typelevel" %% "cats-tagless-macros" % "0.5",
  "org.typelevel" %% "cats-tagless-legacy-macros" % "0.5"
)

addCompilerPlugin(
  "org.scalameta" % "paradise" % "3.0.0-M11" cross CrossVersion.full
)

this code:

import cats.tagless._

case class Element()
case class Id()

@finalAlg
@autoFunctorK(true)
trait MyService[F[_]] {
  def put(element: Element): F[Element]
  def get(elementId: Id): F[Element]
  def all(): F[List[Element]]
  def delete(elementId: Id): F[Unit]
}

compiles just fine, as advertised here.

If I remove addCompilerPlugin("org.scalameta" % "paradise" % "3.0.0-M11" cross CrossVersion.full), I get the same error message:

macro annotation could not be expanded (the most common reason for that is that you need to enable the macro paradise plugin; another possibility is that you try to use macro annotation in the same compilation run that defines it)

Again, this is as documented, the linked page says:

The macro annotations (@finalAlg, @autoFunctorK, @autoInvariantK, etc.) still depends on scalameta, so you need to add scalameta dependencies in build.sbt.

So it seems that you need it because of @finalAlg and @autoFunctorK.

Note that I didn't modify anything in project/.

EDIT

If you have multiple subprojects, you have to add the compiler plugin to the subproject that actually needs it. Notice that

addCompilerPlugin(foobar)

is essentially just

libraryDependencies += compilerPlugin(foobar)

so in your case, you probably should try something like

  libraryDependencies ++= Seq(
    "org.typelevel" %% "cats-core" % "1.6.0",
    "org.typelevel" %% "cats-effect" % "1.2.0",
    "org.typelevel" %% "cats-tagless-macros" % "0.5",
    "org.typelevel" %% "cats-tagless-legacy-macros" % "0.5",
    "org.typelevel" %% "cats-mtl-core" % "0.5.0",
    compilerPlugin(("org.scalameta" % "paradise" % "3.0.0-M11")
      .cross(CrossVersion.full))
  )

and then add this to your algebra subproject.

I added `addCompilerPlugin( ("org.scalameta" % "paradise" % "3.0.0-M11").cross(CrossVersion.full))` and `"org.typelevel" %% "cats-tagless-macros" % latestVersion` and `"org.typelevel" %% "cats-tagless-legacy-macros" % latestVersion` to `build.sbt` and it did not help — Developus, Apr 14 '19 at 15:39
@allocer In what sense did it not help? There are thousand things that could have gone wrong, it's impossible to find out without a proper MCVE. — Andrey Tyukin, Apr 14 '19 at 15:50
@allocer I produced an example that reproduces the error, then I've shown a `build.sbt` that avoids the error. If you have some other example that doesn't work, then you'd have to show it. — Andrey Tyukin, Apr 14 '19 at 15:56
@allocer My last guess so far: take a look at the edit, please. I'm guessing that you somehow added the plugin to the wrong subproject. — Andrey Tyukin, Apr 14 '19 at 16:28
great, it helped to move `compilerPlugin(("org.scalameta" % "paradise" % "3.0.0-M11")(CrossVersion.full))` into commonSettings. Thanks — Developus, Apr 14 '19 at 16:38

Cats-tagless - Scala macro annotation error

1 Answers1