Cats-tagless - Scala 宏注释错误

Question

我使用 cats-tagless 库创建了一个简单的 trait:

@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]
}

但是当我尝试编译它时，出现错误：

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)

我还将 addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.1" cross CrossVersion.full) 添加到 plugins.sbt 文件和 build.sbt 中，但没有帮助。你能帮我解决吗？

我的 build.sbt 文件如下所示：

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",
  )
)

Answer 1

在一个空的新项目中 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
)

此代码：

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]
}

编译得很好，正如所宣传的那样here。

如果我删除 addCompilerPlugin("org.scalameta" % "paradise" % "3.0.0-M11" cross CrossVersion.full)，我会收到相同的错误消息：

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)

同样，这是记录在案的，链接页面说：

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

看来你需要它是因为 @finalAlg 和 @autoFunctorK。

请注意，我没有修改 project/ 中的任何内容。

编辑

如果您有多个子项目，您必须将编译器插件添加到实际需要它的子项目中。请注意

addCompilerPlugin(foobar)

本质上只是

libraryDependencies += compilerPlugin(foobar)

所以在你的情况下，你可能应该尝试像

  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))
  )

然后将其添加到您的 algebra 子项目中。

Cats-tagless - Scala 宏注释错误

Cats-tagless - Scala macro annotation error

scala

scala-macros

scala-cats

scala-macro-paradise