default to never for Runtime returning functions (#2096)

Author: tim-smart

.changeset/brave-rats-travel.md

@@ -0,0 +1,13 @@
+---
+"effect": patch
+---
+
+default to `never` for Runtime returning functions
+
+This includes:
+
+- Effect.runtime
+- FiberSet.makeRuntime
+
+It prevents `unknown` from creeping into types, as well as `never` being a
+useful default type for propogating Fiber Refs and other context.

packages/effect/src/Effect.ts

@@ -4536,7 +4536,7 @@ export const randomWith: <A, E, R>(f: (random: Random.Random) => Effect<A, E, R>
  * @since 2.0.0
  * @category runtime
  */
-export const runtime: <R>() => Effect<Runtime.Runtime<R>, never, R> = _runtime.runtime
+export const runtime: <R = never>() => Effect<Runtime.Runtime<R>, never, R> = _runtime.runtime
 
 /**
  * Retrieves an effect that succeeds with the current runtime flags, which

packages/effect/src/FiberSet.ts

@@ -101,7 +101,7 @@ export const make = <A = unknown, E = unknown>(): Effect.Effect<FiberSet<A, E>,
  * @since 2.0.0
  * @categories constructors
  */
-export const makeRuntime = <R, A = unknown, E = unknown>(): Effect.Effect<
+export const makeRuntime = <R = never, A = unknown, E = unknown>(): Effect.Effect<
   <XE extends E, XA extends A>(
     effect: Effect.Effect<XA, XE, R>,
     options?: Runtime.RunForkOptions | undefined