Make sure Effect.Tag works with primitives (#2257)

Author: mikearnaldi

.changeset/good-dots-sleep.md

@@ -0,0 +1,27 @@
+---
+"effect": patch
+---
+
+Make sure Effect.Tag works on primitives.
+
+This change allows the following to work just fine:
+
+```ts
+import { Effect, Layer } from "effect";
+
+class DateTag extends Effect.Tag("DateTag")<DateTag, Date>() {
+  static date = new Date(1970, 1, 1);
+  static Live = Layer.succeed(this, this.date);
+}
+
+class MapTag extends Effect.Tag("MapTag")<MapTag, Map<string, string>>() {
+  static Live = Layer.effect(
+    this,
+    Effect.sync(() => new Map())
+  );
+}
+
+class NumberTag extends Effect.Tag("NumberTag")<NumberTag, number>() {
+  static Live = Layer.succeed(this, 100);
+}
+```

packages/effect/src/Effect.ts

@@ -5245,18 +5245,18 @@ export const optionFromOptional: <A, E, R>(
  */
 export const Tag: <const Id extends string>(id: Id) => <Self, Type>() =>
   & Context.TagClass<Self, Id, Type>
-  & { _Type: Type }
-  & {
-    [
-      k in keyof Type as Type[k] extends ((...args: [...infer Args]) => infer Ret) ?
-        ((...args: Readonly<Args>) => Ret) extends Type[k] ? k : never
-        : k
-    ]: Type[k] extends (...args: [...infer Args]) => Effect<infer A, infer E, infer R> ?
-      (...args: Readonly<Args>) => Effect<A, E, Self | R>
-      : Type[k] extends (...args: [...infer Args]) => infer A ? (...args: Readonly<Args>) => Effect<A, never, Self>
-      : Type[k] extends Effect<infer A, infer E, infer R> ? Effect<A, E, Self | R>
-      : Effect<Type[k], never, Self>
-  }
+  & (Type extends Record<PropertyKey, any> ? {
+      [
+        k in keyof Type as Type[k] extends ((...args: [...infer Args]) => infer Ret) ?
+          ((...args: Readonly<Args>) => Ret) extends Type[k] ? k : never
+          : k
+      ]: Type[k] extends (...args: [...infer Args]) => Effect<infer A, infer E, infer R> ?
+        (...args: Readonly<Args>) => Effect<A, E, Self | R>
+        : Type[k] extends (...args: [...infer Args]) => infer A ? (...args: Readonly<Args>) => Effect<A, never, Self>
+        : Type[k] extends Effect<infer A, infer E, infer R> ? Effect<A, E, Self | R>
+        : Effect<Type[k], never, Self>
+    } :
+    {})
   & {
     use: <X>(
       body: (_: Type) => X

packages/effect/test/Effect/environment.test.ts

@@ -2,6 +2,7 @@ import * as it from "effect-test/utils/extend"
 import * as Context from "effect/Context"
 import * as Effect from "effect/Effect"
 import { pipe } from "effect/Function"
+import * as Layer from "effect/Layer"
 import { assert, describe, expect } from "vitest"
 
 interface NumberService {
@@ -30,6 +31,19 @@ class DemoTag extends Effect.Tag("DemoTag")<DemoTag, {
 }>() {
 }
 
+class DateTag extends Effect.Tag("DateTag")<DateTag, Date>() {
+  static date = new Date(1970, 1, 1)
+  static Live = Layer.succeed(this, this.date)
+}
+
+class MapTag extends Effect.Tag("MapTag")<MapTag, Map<string, string>>() {
+  static Live = Layer.effect(this, Effect.sync(() => new Map()))
+}
+
+class NumberTag extends Effect.Tag("NumberTag")<NumberTag, number>() {
+  static Live = Layer.succeed(this, 100)
+}
+
 describe("Effect", () => {
   it.effect("effect tag", () =>
     Effect.gen(function*($) {
@@ -51,6 +65,21 @@ describe("Effect", () => {
       fn: (...args) => Array.from(args),
       fnGen: (s) => [s]
     })))
+  it.effect("effect tag with primitives", () =>
+    Effect.gen(function*($) {
+      expect(yield* $(DateTag.getTime())).toEqual(DateTag.date.getTime())
+      expect(yield* $(NumberTag)).toEqual(100)
+      expect(Array.from(yield* $(MapTag.keys()))).toEqual([])
+      yield* $(MapTag.set("foo", "bar"))
+      expect(Array.from(yield* $(MapTag.keys()))).toEqual(["foo"])
+      expect(yield* $(MapTag.get("foo"))).toEqual("bar")
+    }).pipe(
+      Effect.provide(Layer.mergeAll(
+        DateTag.Live,
+        NumberTag.Live,
+        MapTag.Live
+      ))
+    ))
   it.effect("class tag", () =>
     Effect.gen(function*($) {
       yield* $(