Add rules to convert .map(_ => f) to .as(f) and .map(_ => ()) to .void

modules/cats/input/src/main/scala/fix/AsTests.scala

@@ -0,0 +1,27 @@
+/*
+rule = TypelevelAs
+ */
+package fix
+
+object AsTests {
+
+  def listMapLit = {
+    List(1, 2, 3).map(_ => 1) /* assert: TypelevelAs.as
+    ^^^^^^^^^^^^^^^^^^^^^^^^^
+    .map(_ => f) can be replaced by .as(f) */
+  }
+
+  def listMapUnit = {
+    List(1, 2, 3).map(_ => ()) /* assert: TypelevelAs.as
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^
+    .map(_ => ()) can be replaced by .void */
+  }
+
+  def shouldBeIgnored = {
+    def f = "a"
+    List(1, 2, 3).map(_ => f)
+    List(1, 2, 3).map(i => i)
+    List(1, 2, 3).map(println(_))
+  }
+
+}

modules/cats/rules/src/main/resources/META-INF/services/scalafix.v1.Rule

@@ -1,2 +1,3 @@
 org.typelevel.fix.MapSequence
 org.typelevel.fix.UnusedShowInterpolator
+org.typelevel.fix.As

modules/cats/rules/src/main/scala/org/typelevel/fix/As.scala

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2022 Typelevel
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.typelevel.fix
+
+import scalafix.v1._
+import scala.meta._
+
+class As extends SemanticRule("TypelevelAs") {
+  override def fix(implicit doc: SemanticDocument): Patch =
+    doc.tree.collect {
+      // fa.map(_ => ())
+      case tree @ AnonymousMap(Lit.Unit()) => Patch.lint(VoidDiagnostic(tree))
+      // fa.map(_ => 1)
+      case tree @ AnonymousMap(_: Lit) => Patch.lint(AsDiagnostic(tree))
+    }.asPatch
+
+}
+
+object AnonymousMap {
+  def unapply(term: Term): Option[Term] = term match {
+    case Term.Apply(
+          Term.Select(_, Term.Name("map")),
+          Term.Function(List(Term.Param(_, Name.Anonymous(), _, _)), returnType) :: Nil
+        ) =>
+      Some(returnType)
+    case _ => None
+  }
+}
+
+final case class AsDiagnostic(t: Tree) extends Diagnostic {
+  override def message: String    = ".map(_ => f) can be replaced by .as(f)"
+  override def position: Position = t.pos
+  override def categoryID: String = "as"
+}
+
+final case class VoidDiagnostic(t: Tree) extends Diagnostic {
+  override def message: String    = ".map(_ => ()) can be replaced by .void"
+  override def position: Position = t.pos
+  override def categoryID: String = "as"
+}