cats.mtl.Local[IO, E] from IOLocal[E]

build.sbt

@@ -301,6 +301,7 @@ ThisBuild / apiURL := Some(url("https://typelevel.org/cats-effect/api/3.x/"))
 ThisBuild / autoAPIMappings := true
 
 val CatsVersion = "2.11.0"
+val CatsMtlVersion = "1.3.0"
 val Specs2Version = "4.20.5"
 val ScalaCheckVersion = "1.17.1"
 val DisciplineVersion = "1.4.0"
@@ -463,6 +464,9 @@ lazy val core = crossProject(JSPlatform, JVMPlatform, NativePlatform)
   .dependsOn(kernel, std)
   .settings(
     name := "cats-effect",
+    libraryDependencies ++= Seq(
+      "org.typelevel" %%% "cats-mtl" % CatsMtlVersion
+    ),
     mimaBinaryIssueFilters ++= Seq(
       // introduced by #1837, removal of package private class
       ProblemFilters.exclude[MissingClassProblem]("cats.effect.AsyncPropagateCancelation"),
@@ -902,7 +906,8 @@ lazy val tests: CrossProject = crossProject(JSPlatform, JVMPlatform, NativePlatf
       "org.scalacheck" %%% "scalacheck" % ScalaCheckVersion,
       "org.specs2" %%% "specs2-scalacheck" % Specs2Version % Test,
       "org.typelevel" %%% "discipline-specs2" % DisciplineVersion % Test,
-      "org.typelevel" %%% "cats-kernel-laws" % CatsVersion % Test
+      "org.typelevel" %%% "cats-kernel-laws" % CatsVersion % Test,
+      "org.typelevel" %%% "cats-mtl-laws" % CatsMtlVersion % Test
     ),
     githubWorkflowArtifactUpload := false
   )

core/shared/src/main/scala/cats/effect/IO.scala

@@ -1949,6 +1949,9 @@ object IO extends IOCompanionPlatform with IOLowPriorityImplicits with TuplePara
       case Failure(err) => raiseError(err)
     }
 
+  def local[E](e: E): IO[cats.mtl.Local[IO, E]] =
+    IOLocal(e).map(_.asLocal)
+
   // instances
 
   implicit def showForIO[A: Show]: Show[IO[A]] =

core/shared/src/main/scala/cats/effect/IOLocal.scala

@@ -16,7 +16,9 @@
 
 package cats.effect
 
+import cats.Applicative
 import cats.data.AndThen
+import cats.mtl.Local
 
 /**
  * [[IOLocal]] provides a handy way of manipulating a context on different scopes.
@@ -238,6 +240,17 @@ sealed trait IOLocal[A] extends IOLocalPlatform[A] { self =>
    */
   def lens[B](get: A => B)(set: A => B => A): IOLocal[B]
 
+  final def asLocal: Local[IO, A] =
+    new Local[IO, A] {
+      def applicative: Applicative[IO] =
+        IO.asyncForIO
+
+      def ask[A2 >: A] =
+        self.get
+
+      def local[B](iob: IO[B])(f: A => A): IO[B] =
+        self.modify(e => f(e) -> e).bracket(Function.const(iob))(self.set)
+    }
 }
 
 object IOLocal {
@@ -312,5 +325,4 @@ object IOLocal {
       new IOLocalLens(underlying, getter, setter)
     }
   }
-
 }

tests/shared/src/test/scala/cats/effect/IOMtlLocalSpec.scala

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2020-2022 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 cats
+package effect
+
+import cats.mtl.Local
+import cats.mtl.laws.discipline._
+
+import org.typelevel.discipline.specs2.mutable.Discipline
+
+import java.util.concurrent.CancellationException
+
+class IOMtlLocalSpec extends BaseSpec with Discipline {
+  sequential
+
+  implicit val ticker: Ticker = Ticker()
+
+  implicit val local: Local[IO, Int] =
+    // Don't try this at home
+    unsafeRun(IO.local(0)).fold(
+      throw new CancellationException("canceled"),
+      throw _,
+      _.get
+    )
+
+  checkAll("Local[IO, Int]", LocalTests[IO, Int].local[Int, Int])
+}