Add scalafix for contramap

scalafix/input/src/main/scala/fix/v1_0_0/ContraMapToLMap.scala

@@ -0,0 +1,31 @@
+/*
+rule = "scala:fix.v1_0_0.ContraMapToLMap"
+ */
+package fix
+package to1_0_0
+
+
+
+object ContraMapToLMapTests {
+  import cats.Show
+  import cats.syntax.all._
+  import cats.instances.all._
+
+  val f: Int => String = _.toString
+
+  val g: Int => String = f.contramap(_ + 1)
+
+  object Foo
+  object Bar
+  object Baz
+
+  implicit val showFoo: Show[Foo.type] = Show.fromToString
+
+  val showBar: Show[Bar.type] = showFoo.contramap(_ => Foo)
+
+  val showBaz: Show[Baz.type] = Show[Foo.type].contramap(_ => Foo)
+
+  def getShowBar(): Show[Bar.type] = showBar
+
+  getShowBar().contramap((_: Int) => Bar)
+}

scalafix/output/src/main/scala/fix/v1_0_0/ContraMapToLMap.scala

@@ -0,0 +1,28 @@
+package fix
+package to1_0_0
+
+
+
+object ContraMapToLMapTests {
+  import cats.Show
+  import cats.syntax.all._
+  import cats.instances.all._
+
+  val f: Int => String = _.toString
+
+  val g: Int => String = f.lmap(_ + 1)
+
+  object Foo
+  object Bar
+  object Baz
+
+  implicit val showFoo: Show[Foo.type] = Show.fromToString
+
+  val showBar: Show[Bar.type] = showFoo.contramap(_ => Foo)
+
+  val showBaz: Show[Baz.type] = Show[Foo.type].contramap(_ => Foo)
+
+  def getShowBar(): Show[Bar.type] = showBar
+
+  getShowBar().contramap((_: Int) => Bar)
+}

scalafix/rules/src/main/scala/fix/Cats_v1_0_0.scala

@@ -2,6 +2,7 @@ package fix
 package v1_0_0
 
 import scalafix._
+import scalafix.syntax._
 import scalafix.util.SymbolMatcher
 import scala.meta._
 import scala.meta.contrib._
@@ -73,6 +74,30 @@ case class RemoveCartesianBuilder(index: SemanticdbIndex)
   }
 }
 
+// ref: https://github.com/typelevel/cats/issues/1850
+case class ContraMapToLMap(index: SemanticdbIndex)
+  extends SemanticRule(index, "UseLMapInsteadOfContraMap") {
+
+  override def fix(ctx: RuleCtx): Patch = {
+
+    val contraMatcher = SymbolMatcher.normalized(Symbol("_root_.cats.functor.Contravariant.Ops.`contramap`."))
+
+    val unApplyName = "catsUnapply2left"
+
+    ctx.tree.collect {
+      case Term.Apply(fun, _) =>
+        if (contraMatcher.matches(fun) &&
+          fun.children.headOption.flatMap(index.denotation).exists(_.name == unApplyName )) {
+          fun.children.find(contraMatcher.matches).map(tree => ctx.replaceTree(tree, "lmap")).getOrElse(Patch.empty)
+        } else {
+          Patch.empty
+        }
+      case _ => Patch.empty
+
+    }.asPatch
+  }
+}
+
 // ref: https://github.com/typelevel/cats/pull/1583
 case class RemoveUnapply(index: SemanticdbIndex)
     extends SemanticRule(index, "RemoveUnapply") {