Add ZLayer#toManaged (zio#8211)

Author: neko-kai

managed-tests/shared/src/test/scala/zio/managed/ZManagedSpec.scala

@@ -1844,7 +1844,24 @@ object ZManagedSpec extends ZIOBaseSpec {
         _     <- endLatch.await
         res   <- release.get
       } yield assertTrue(res)
-    }
+    },
+    suite("toManaged")(
+      test("preserve lifecycle of a layer converted to a managed value") {
+        def sideEffectingLayer(ref: Ref[Int]): ZLayer[Any, Nothing, String] =
+          ZLayer.scoped {
+            ZIO.scopeWith(_.addFinalizerExit(_ => ref.update(_ + 2)))
+          } >>>
+            ZLayer(ref.update(_ + 1).as("Howdy"))
+
+        for {
+          ref <- Ref.make(0)
+          res1 <- sideEffectingLayer(ref).toManaged.use { env =>
+                    ref.get.map(_ -> env.get[String])
+                  }
+          res2 <- ref.get
+        } yield assertTrue(res1._1 == 1) && assertTrue(res1._2 == "Howdy") && assertTrue(res2 == 3)
+      }
+    )
   )
 
   val ExampleError = new Throwable("Oh noes!")

managed/shared/src/main/scala/zio/managed/package.scala

@@ -107,6 +107,13 @@ package object managed extends ZManagedCompatPlatformSpecific {
       ZManaged.fromReservationZIO(reservation).use(use)
   }
 
+  implicit final class ZManagedZLayerSyntax[R, E, A](private val self: ZLayer[R, E, A]) extends AnyVal {
+
+    /** Converts this layer to a ZManaged value. */
+    def toManaged(implicit trace: Trace): ZManaged[R, E, ZEnvironment[A]] =
+      ZManaged.scoped[R](self.build)
+  }
+
   implicit final class ZManagedZLayerCompanionSyntax(private val self: ZLayer.type) extends AnyVal {
 
     /**