From b95558e3d6183fe3310982707c7c17b73da1c6ff Mon Sep 17 00:00:00 2001
From: Michael Arnaldi <michael.arnaldi@effectful.co>
Date: Thu, 26 Sep 2024 18:10:00 +0200
Subject: [PATCH] Support providing an array of layers via Effect.provide

---
 .changeset/old-ways-accept.md               |  5 ++++
 packages/effect/src/Effect.ts               | 21 ++++++++++++++-
 packages/effect/src/internal/layer.ts       | 30 +++++++++++++++++++--
 packages/effect/test/Effect/service.test.ts |  6 ++++-
 4 files changed, 58 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/old-ways-accept.md

diff --git a/.changeset/old-ways-accept.md b/.changeset/old-ways-accept.md
new file mode 100644
index 0000000000..dc0e95f028
--- /dev/null
+++ b/.changeset/old-ways-accept.md
@@ -0,0 +1,5 @@
+---
+"effect": minor
+---
+
+Support providing an array of layers via Effect.provide
diff --git a/packages/effect/src/Effect.ts b/packages/effect/src/Effect.ts
index 2da939a9cb..cc1478b3de 100644
--- a/packages/effect/src/Effect.ts
+++ b/packages/effect/src/Effect.ts
@@ -3325,11 +3325,30 @@ export const mapInputContext: {
  * @category context
  */
 export const provide: {
+  <const Layers extends [Layer.Layer<any, any, any>, ...Array<Layer.Layer<any, any, any>>]>(
+    layers: Layers
+  ): <A, E, R>(
+    self: Effect<A, E, R>
+  ) => Effect<
+    A,
+    E | { [k in keyof Layers]: Layer.Layer.Error<Layers[k]> }[number],
+    | { [k in keyof Layers]: Layer.Layer.Context<Layers[k]> }[number]
+    | Exclude<R, { [k in keyof Layers]: Layer.Layer.Success<Layers[k]> }[number]>
+  >
   <ROut, E2, RIn>(
     layer: Layer.Layer<ROut, E2, RIn>
-  ): <A, E, R>(self: Effect<A, E, R>) => Effect<A, E2 | E, RIn | Exclude<R, ROut>>
+  ): <A, E, R>(self: Effect<A, E, R>) => Effect<A, E | E2, RIn | Exclude<R, ROut>>
   <R2>(context: Context.Context<R2>): <A, E, R>(self: Effect<A, E, R>) => Effect<A, E, Exclude<R, R2>>
   <R2>(runtime: Runtime.Runtime<R2>): <A, E, R>(self: Effect<A, E, R>) => Effect<A, E, Exclude<R, R2>>
+  <A, E, R, const Layers extends [Layer.Layer<any, any, any>, ...Array<Layer.Layer<any, any, any>>]>(
+    self: Effect<A, E, R>,
+    layers: Layers
+  ): Effect<
+    A,
+    E | { [k in keyof Layers]: Layer.Layer.Error<Layers[k]> }[number],
+    | { [k in keyof Layers]: Layer.Layer.Context<Layers[k]> }[number]
+    | Exclude<R, { [k in keyof Layers]: Layer.Layer.Success<Layers[k]> }[number]>
+  >
   <A, E, R, ROut, E2, RIn>(
     self: Effect<A, E, R>,
     layer: Layer.Layer<ROut, E2, RIn>
diff --git a/packages/effect/src/internal/layer.ts b/packages/effect/src/internal/layer.ts
index dd6786ab5f..b6b6583001 100644
--- a/packages/effect/src/internal/layer.ts
+++ b/packages/effect/src/internal/layer.ts
@@ -1291,6 +1291,16 @@ const provideSomeRuntime = dual<
 /** @internal */
 export const effect_provide = dual<
   {
+    <const Layers extends [Layer.Layer<any, any, any>, ...Array<Layer.Layer<any, any, any>>]>(
+      layers: Layers
+    ): <A, E, R>(
+      self: Effect.Effect<A, E, R>
+    ) => Effect.Effect<
+      A,
+      E | { [k in keyof Layers]: Layer.Layer.Error<Layers[k]> }[number],
+      | { [k in keyof Layers]: Layer.Layer.Context<Layers[k]> }[number]
+      | Exclude<R, { [k in keyof Layers]: Layer.Layer.Success<Layers[k]> }[number]>
+    >
     <ROut, E2, RIn>(
       layer: Layer.Layer<ROut, E2, RIn>
     ): <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E | E2, RIn | Exclude<R, ROut>>
@@ -1302,6 +1312,15 @@ export const effect_provide = dual<
     ): <A, E, R>(self: Effect.Effect<A, E, R>) => Effect.Effect<A, E, Exclude<R, R2>>
   },
   {
+    <A, E, R, const Layers extends [Layer.Layer<any, any, any>, ...Array<Layer.Layer<any, any, any>>]>(
+      self: Effect.Effect<A, E, R>,
+      layers: Layers
+    ): Effect.Effect<
+      A,
+      E | { [k in keyof Layers]: Layer.Layer.Error<Layers[k]> }[number],
+      | { [k in keyof Layers]: Layer.Layer.Context<Layers[k]> }[number]
+      | Exclude<R, { [k in keyof Layers]: Layer.Layer.Success<Layers[k]> }[number]>
+    >
     <A, E, R, ROut, E2, RIn>(
       self: Effect.Effect<A, E, R>,
       layer: Layer.Layer<ROut, E2, RIn>
@@ -1319,9 +1338,16 @@ export const effect_provide = dual<
   2,
   <A, E, R, ROut>(
     self: Effect.Effect<A, E, R>,
-    source: Layer.Layer<ROut, any, any> | Context.Context<ROut> | Runtime.Runtime<ROut>
+    source:
+      | Layer.Layer<ROut, any, any>
+      | Context.Context<ROut>
+      | Runtime.Runtime<ROut>
+      | Array<Layer.Layer<any, any, any>>
   ): Effect.Effect<any, any, Exclude<R, ROut>> =>
-    isLayer(source)
+    Array.isArray(source)
+      // @ts-expect-error
+      ? provideSomeLayer(self, mergeAll(...source)) :
+      isLayer(source)
       ? provideSomeLayer(self, source as Layer.Layer<ROut, any, any>)
       : Context.isContext(source)
       ? core.provideSomeContext(self, source)
diff --git a/packages/effect/test/Effect/service.test.ts b/packages/effect/test/Effect/service.test.ts
index 8fc9315436..6f576c994f 100644
--- a/packages/effect/test/Effect/service.test.ts
+++ b/packages/effect/test/Effect/service.test.ts
@@ -34,7 +34,11 @@ describe("Effect", () => {
       expect(_tag).toEqual("Logger")
       yield* Logger.info("Ok")
       expect(messages).toEqual(["[PRE][Ok][POST]"])
+      const { prefix } = yield* Prefix
+      expect(prefix).toEqual("PRE")
+      const { postfix } = yield* Postfix
+      expect(postfix).toEqual("POST")
     }).pipe(
-      Effect.provide(Logger)
+      Effect.provide([Logger, Prefix, Postfix])
     ))
 })