fix Micro.forEach for empty iterables (#3545)

.changeset/two-rings-compare.md

@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+fix Micro.forEach for empty iterables

packages/effect/src/Micro.ts

@@ -2594,9 +2594,11 @@ export const withTrace: {
   const f = (name: string) => (self: Micro<any, any, any>) =>
     unsafeMakeOptions(function(env, onExit) {
       self[runSymbol](env, function(exit) {
+        console.log(name, exit)
         onExit(exit._tag === "Left" ? Either.left(generate(name, exit.left)) : exit)
       })
     }, false)
+  console.log(arguments.length)
   if (arguments.length === 2) {
     return f(arguments[1])(arguments[0])
   }
@@ -3465,6 +3467,9 @@ export const forEach: {
     let result: MicroExit<any, any> | undefined = undefined
     const items = Array.from(iterable)
     let length = items.length
+    if (length === 0) {
+      return onExit(Either.right(options?.discard ? undefined : []))
+    }
     const out: Array<B> | undefined = options?.discard ? undefined : new Array(length)
     let index = 0
     let inProgress = 0
@@ -3949,6 +3954,7 @@ export const runSyncExit = <A, E>(effect: Micro<A, E>): MicroExit<A, E> => {
   const handle = runFork(effect, { scheduler })
   scheduler.flush()
   const exit = handle.unsafePoll()
+  console.log(exit)
   if (exit === null) {
     return exitDie(handle)
   }

packages/effect/test/Micro.test.ts

@@ -232,6 +232,12 @@ describe.concurrent("Micro", () => {
         assert.deepStrictEqual(result, Micro.exitFail("error"))
         assert.deepStrictEqual(done, [1, 2, 3])
       }).pipe(Micro.runPromise))
+
+    it("length = 0", () =>
+      Micro.gen(function*() {
+        const results = yield* Micro.forEach([], (_) => Micro.succeed(_))
+        assert.deepStrictEqual(results, [])
+      }).pipe(Micro.runPromise))
   })
 
   describe("all", () => {