zio · jdegoes · Feb 15, 2020 · Feb 15, 2020 · jdegoes · Feb 15, 2020
diff --git a/core-tests/shared/src/test/scala/zio/ZIOSpec.scala b/core-tests/shared/src/test/scala/zio/ZIOSpec.scala
@@ -1210,6 +1210,14 @@ object ZIOSpec extends ZIOBaseSpec {
         } yield assert(res._1)(equalTo(List(0, 2, 4, 6, 8))) && assert(res._2)(equalTo(List(1, 3, 5, 7, 9)))
       }
     ),
+    suite("provideCustomLayer")(
+      testM("provides the part of the environment that is not part of the `ZEnv`") {
+        val loggingLayer: ZLayer[Any, Nothing, Logging] = Logging.live
+        val zio: ZIO[ZEnv with Logging, Nothing, Unit]  = ZIO.unit
+        val zio2: ZIO[ZEnv, Nothing, Unit]              = zio.provideCustomLayer(loggingLayer)
+        assertM(zio2)(anything)
+      }
+    ),
     suite("provideSomeLayer")(
       testM("can split environment into two parts") {
         val clockLayer: ZLayer[Any, Nothing, Clock]    = Clock.live
@@ -3032,4 +3040,11 @@ object ZIOSpec extends ZIOBaseSpec {
       } yield v1 + v2
 
   def AsyncUnit[E] = IO.effectAsync[E, Unit](_(IO.unit))
+
+  type Logging = Has[Logging.Service]
+
+  object Logging {
+    trait Service
+    val live: ZLayer[Any, Nothing, Logging] = ZLayer.succeed(new Logging.Service {})
+  }
 }
diff --git a/core/shared/src/main/scala/zio/ZIO.scala b/core/shared/src/main/scala/zio/ZIO.scala
@@ -936,6 +936,23 @@ sealed trait ZIO[-R, +E, +A] extends Serializable with ZIOPlatformSpecific[R, E,
    */
   final def provide(r: R)(implicit ev: NeedsEnv[R]): IO[E, A] = ZIO.provide(r)(self)
 
+  /**
+   * Provides the part of the environment that is not part of the `ZEnv`,
+   * leaving an effect that only depends on the `ZEnv`.
+   *
+   * {{{
+   * val loggingLayer: ZLayer[Any, Nothing, Logging] = ???
+   *
+   * val zio: ZIO[ZEnv with Logging, Nothing, Unit] = ???
+   *
+   * val zio2 = zio.provideCustomLayer(loggingLayer)
+   * }}}
+   */
+  final def provideCustomLayer[E1 >: E, R1 <: Has[_]](
+    layer: ZLayer[ZEnv, E1, R1]
+  )(implicit ev: ZEnv with R1 <:< R, tagged: Tagged[R1]): ZIO[ZEnv, E1, A] =
+    provideSomeLayer[ZEnv](layer)
+
   /**
    * Provides a layer to the ZIO effect, which translates it to another level.
    */

diff --git a/core/shared/src/main/scala/zio/ZManaged.scala b/core/shared/src/main/scala/zio/ZManaged.scala
@@ -643,6 +643,23 @@ final class ZManaged[-R, +E, +A] private (reservation: ZIO[R, E, Reservation[R,
   def provide(r: R)(implicit ev: NeedsEnv[R]): Managed[E, A] =
     provideSome(_ => r)
 
+  /**
+   * Provides the part of the environment that is not part of the `ZEnv`,
+   * leaving a managed effect that only depends on the `ZEnv`.
+   *
+   * {{{
+   * val loggingLayer: ZLayer[Any, Nothing, Logging] = ???
+   *
+   * val managed: ZManaged[ZEnv with Logging, Nothing, Unit] = ???
+   *
+   * val managed2 = managed.provideCustomLayer(loggingLayer)
+   * }}}
+   */
+  def provideCustomLayer[E1 >: E, R1 <: Has[_]](
+    layer: ZLayer[ZEnv, E1, R1]
+  )(implicit ev: ZEnv with R1 <:< R, tagged: Tagged[R1]): ZManaged[ZEnv, E1, A] =
+    provideSomeLayer[ZEnv](layer)
+
   /**
    * Provides a layer to the `ZManaged`, which translates it to another level.
    */

diff --git a/streams/shared/src/main/scala/zio/stream/ZStream.scala b/streams/shared/src/main/scala/zio/stream/ZStream.scala
@@ -2079,6 +2079,23 @@ class ZStream[-R, +E, +A] private[stream] (private[stream] val structure: ZStrea
   final def provide(r: R)(implicit ev: NeedsEnv[R]): Stream[E, A] =
     ZStream(self.process.provide(r).map(_.provide(r)))
 
+  /**
+   * Provides the part of the environment that is not part of the `ZEnv`,
+   * leaving a stream that only depends on the `ZEnv`.
+   *
+   * {{{
+   * val loggingLayer: ZLayer[Any, Nothing, Logging] = ???
+   *
+   * val stream: ZStream[ZEnv with Logging, Nothing, Unit] = ???
+   *
+   * val stream2 = stream.provideCustomLayer(loggingLayer)
+   * }}}
+   */
+  def provideCustomLayer[E1 >: E, R1 <: Has[_]](
+    layer: ZLayer[ZEnv, E1, R1]
+  )(implicit ev: ZEnv with R1 <:< R, tagged: Tagged[R1]): ZStream[ZEnv, E1, A] =
+    provideSomeLayer[ZEnv](layer)
+
   /**
    * An effectual version of `provide`, useful when the act of provision
    * requires an effect.

diff --git a/test-tests/shared/src/test/scala/zio/test/SpecSpec.scala b/test-tests/shared/src/test/scala/zio/test/SpecSpec.scala
@@ -3,6 +3,7 @@ package zio.test
 import zio.test.Assertion.{ equalTo, isFalse, isTrue }
 import zio.test.TestAspect.ifEnvSet
 import zio.test.TestUtils._
+import zio.test.environment.TestEnvironment
 import zio.{ Has, Ref, UIO, ZIO, ZLayer, ZManaged }
 
 object SpecSpec extends ZIOBaseSpec {
@@ -85,6 +86,14 @@ object SpecSpec extends ZIOBaseSpec {
         } yield assert(passed)(isFalse)
       }
     ),
+    suite("provideCustomLayer")(
+      testM("provides the part of the environment that is not part of the `TestEnvironment`") {
+        for {
+          _ <- ZIO.environment[TestEnvironment]
+          _ <- ZIO.environment[Module]
+        } yield assertCompletes
+      }.provideCustomLayer(layer)
+    ),
     suite("provideLayer")(
       testM("does not have early initialization issues") {
         for {

diff --git a/test/shared/src/main/scala/zio/test/Spec.scala b/test/shared/src/main/scala/zio/test/Spec.scala
@@ -16,9 +16,9 @@
 
 package zio.test
 
-import Spec._
-
 import zio._
+import zio.test.Spec._
+import zio.test.environment.TestEnvironment
 
 /**
  * A `Spec[R, E, T]` is the backbone of _ZIO Test_. Every spec is either a
@@ -300,6 +300,42 @@ final case class Spec[-R, +E, +T](caseValue: SpecCase[R, E, T, Spec[R, E, T]]) {
   final def provide(r: R)(implicit ev: NeedsEnv[R]): Spec[Any, E, T] =
     provideM(ZIO.succeedNow(r))
 
+  /**
+   * Provides each test with the part of the environment that is not part of
+   * the `TestEnvironment`, leaving a spec that only depends on the
+   * `TestEnvironment`.
+   *
+   * {{{
+   * val loggingLayer: ZLayer[Any, Nothing, Logging] = ???
+   *
+   * val spec: ZSpec[TestEnvironment with Logging, Nothing] = ???
+   *
+   * val spec2 = spec.provideCustomLayer(loggingLayer)
+   * }}}
+   */
+  def provideCustomLayer[E1 >: E, R1 <: Has[_]](
+    layer: ZLayer[TestEnvironment, E1, R1]
+  )(implicit ev: TestEnvironment with R1 <:< R, tagged: Tagged[R1]): Spec[TestEnvironment, E1, T] =
+    provideSomeLayer[TestEnvironment](layer)
+
+  /**
+   * Provides all tests with a shared version of the part of the environment
+   * that is not part of the `TestEnvironment`, leaving a spec that only
+   * depends on the `TestEnvironment`.
+   *
+   * {{{
+   * val loggingLayer: ZLayer[Any, Nothing, Logging] = ???
+   *
+   * val spec: ZSpec[TestEnvironment with Logging, Nothing] = ???
+   *
+   * val spec2 = spec.provideCustomLayerShared(loggingLayer)
+   * }}}
+   */
+  def provideCustomLayerShared[E1 >: E, R1 <: Has[_]](
+    layer: ZLayer[TestEnvironment, E1, R1]
+  )(implicit ev: TestEnvironment with R1 <:< R, tagged: Tagged[R1]): Spec[TestEnvironment, E1, T] =
+    provideSomeLayerShared[TestEnvironment](layer)
+
   /**
    * Provides a layer to the spec, translating it up a level.
    */
@@ -374,9 +410,9 @@ final case class Spec[-R, +E, +T](caseValue: SpecCase[R, E, T, Spec[R, E, T]]) {
    * {{{
    * val clockLayer: ZLayer[Any, Nothing, Clock] = ???
    *
-   * val spec: ZIO[Clock with Random, Nothing, Unit] = ???
+   * val spec: ZSpec[Clock with Random, Nothing] = ???
    *
-   * val zio2 = zio.provideSomeLayer[Random](clockLayer)
+   * val spec2 = spec.provideSomeLayerShared[Random](clockLayer)
    * }}}
    */
   final def provideSomeLayerShared[R0 <: Has[_]]: Spec.ProvideSomeLayerShared[R0, R, E, T] =