add KindProjector

Author: xuwei-k

build.sbt

@@ -17,6 +17,8 @@ val commonSettings = Def.settings(
   },
   scalacOptions ++= Seq(
     "-deprecation",
+    "-language:higherKinds",
+    "-feature",
   ),
   pomExtra := (
     <developers>
@@ -102,6 +104,13 @@ lazy val rules = projectMatrix
 
 lazy val inputOutputCommon = Def.settings(
   libraryDependencies += "org.scala-lang.modules" %% "scala-collection-compat" % "2.6.0",
+  libraryDependencies ++= {
+    if (scalaBinaryVersion.value != "3") {
+      Seq(compilerPlugin("org.typelevel" %% "kind-projector" % "0.13.2" cross CrossVersion.full))
+    } else {
+      Nil
+    }
+  },
   libraryDependencies ++= {
     if (scalaBinaryVersion.value == "2.13") {
       Seq("io.circe" %% "circe-generic-extras" % "0.14.1")

input/src/main/scala-2/fix/KindProjectorTest.scala

@@ -0,0 +1,13 @@
+/*
+rule = KindProjector
+ */
+package fix
+
+import cats.data.Validated
+
+trait KindProjectorTest {
+  def f1: Functor[String Either *]
+  def f2: Functor[Int Validated *]
+}
+
+trait Functor[F[_]]

output/src/main/scala-2/fix/KindProjectorTest.scala

@@ -0,0 +1,10 @@
+package fix
+
+import cats.data.Validated
+
+trait KindProjectorTest {
+  def f1: Functor[Either[String, *]]
+  def f2: Functor[Validated[Int, *]]
+}
+
+trait Functor[F[_]]

rules/src/main/scala/fix/KindProjector.scala

@@ -0,0 +1,57 @@
+package fix
+
+import metaconfig.ConfDecoder
+import metaconfig.Configured
+import metaconfig.generic.Surface
+import scalafix.Patch
+import scalafix.v1.Configuration
+import scalafix.v1.Rule
+import scalafix.v1.SyntacticDocument
+import scalafix.v1.SyntacticRule
+import scala.meta.Type
+
+case class KindProjectorConfig(
+  rewriteInfixTypes: Set[String]
+)
+
+object KindProjectorConfig {
+  val default: KindProjectorConfig = KindProjectorConfig(
+    rewriteInfixTypes = Set.empty
+  )
+
+  implicit val surface: Surface[KindProjectorConfig] =
+    metaconfig.generic.deriveSurface[KindProjectorConfig]
+
+  implicit val decoder: ConfDecoder[KindProjectorConfig] =
+    metaconfig.generic.deriveDecoder(default)
+}
+
+/**
+  * [[https://github.com/lampepfl/dotty-feature-requests/issues/117]]
+  */
+class KindProjector(config: KindProjectorConfig) extends SyntacticRule("KindProjector") {
+  def this() = this(KindProjectorConfig.default)
+
+  override def withConfiguration(config: Configuration): Configured[Rule] = {
+    config.conf.getOrElse("KindProjector")(this.config).map(newConfig => new KindProjector(newConfig))
+  }
+
+  private[this] object InfixOpExtractor {
+    def unapply(name: Type.Name): Option[String] = {
+      if (config.rewriteInfixTypes.isEmpty) {
+        // rewrite all if config isEmpty
+        Some(name.value)
+      } else if (config.rewriteInfixTypes(name.value)) {
+        Some(name.value)
+      } else {
+        None
+      }
+    }
+  }
+
+  override def fix(implicit doc: SyntacticDocument): Patch = {
+    doc.tree.collect { case t @ Type.ApplyInfix(left, InfixOpExtractor(opName), Type.Name("*")) =>
+      Patch.replaceTree(t, s"${opName}[${left}, *]")
+    }.asPatch
+  }
+}