fix(rstream): subscribe() w/ xform, add test

- fixes `.subscribe(sub, xform)` where child `sub` was an actual instance
  of `Subscription` and the given `xform` transducer was silently
  ignored in that case...
- add test

packages/rstream/src/subscription.ts

@@ -157,7 +157,7 @@ export class Subscription<A, B>
             default:
                 illegalArity(args.length);
         }
-        if (implementsFunction(sub!, "subscribe")) {
+        if (implementsFunction(sub!, "subscribe") && !opts.xform) {
             sub!.parent = this;
         } else {
             // FIXME inherit options from this sub or defaults?
@@ -226,19 +226,17 @@ export class Subscription<A, B>
             this.cleanup();
             return res;
         }
-        if (this.subs) {
-            LOGGER.debug(this.id, "unsub child", sub.id);
-            const idx = this.subs.indexOf(sub);
-            if (idx >= 0) {
-                this.subs.splice(idx, 1);
-                if (
-                    this.closeOut === CloseMode.FIRST ||
-                    (!this.subs.length && this.closeOut !== CloseMode.NEVER)
-                ) {
-                    this.unsubscribe();
-                }
-                return true;
+        LOGGER.debug(this.id, "unsub child", sub.id);
+        const idx = this.subs.indexOf(sub);
+        if (idx >= 0) {
+            this.subs.splice(idx, 1);
+            if (
+                this.closeOut === CloseMode.FIRST ||
+                (!this.subs.length && this.closeOut !== CloseMode.NEVER)
+            ) {
+                this.unsubscribe();
             }
+            return true;
         }
         return false;
     }
@@ -252,9 +250,7 @@ export class Subscription<A, B>
                 for (let i = 0; i < n; i++) {
                     this.dispatch(uacc[i]);
                 }
-                if (isReduced(acc)) {
-                    this.done();
-                }
+                isReduced(acc) && this.done();
             } else {
                 this.dispatch(<any>x);
             }
@@ -273,7 +269,7 @@ export class Subscription<A, B>
                 }
             }
             this.state = State.DONE;
-            for (let s of [...this.subs]) {
+            for (let s of this.subs.slice()) {
                 try {
                     s.done && s.done();
                 } catch (e) {
@@ -287,9 +283,10 @@ export class Subscription<A, B>
 
     error(e: any) {
         this.state = State.ERROR;
+        const subs = this.subs;
         let notified = false;
-        if (this.subs && this.subs.length) {
-            for (let s of this.subs.slice()) {
+        if (subs.length) {
+            for (let s of subs.slice()) {
                 if (s.error) {
                     s.error(e);
                     notified = true;
@@ -316,17 +313,18 @@ export class Subscription<A, B>
         // LOGGER.debug(this.id, "dispatch", x);
         this.cacheLast && (this.last = x);
         const subs = this.subs;
+        let n = subs.length;
         let s: ISubscriber<B>;
-        if (subs.length === 1) {
+        if (n === 1) {
             s = subs[0];
             try {
                 s.next && s.next(x);
             } catch (e) {
                 s.error ? s.error(e) : this.error(e);
             }
         } else {
-            for (let i = subs.length; --i >= 0; ) {
-                s = subs[i];
+            for (; --n >= 0; ) {
+                s = subs[n];
                 try {
                     s.next && s.next(x);
                 } catch (e) {

packages/rstream/test/subscription.ts

@@ -6,6 +6,7 @@ import {
     Stream,
     fromIterableSync,
     CloseMode,
+    subscription,
 } from "../src/index";
 import { TIMEOUT } from "./config";
 
@@ -128,8 +129,20 @@ describe("Subscription", () => {
                     buf.push(x);
                 },
             },
-            map((x: number) => x + 10),
-            undefined
+            map((x: number) => x + 10)
+        );
+        assert.deepEqual(buf, [11]);
+    });
+
+    it("child sub w/ xform", () => {
+        let buf: any[] = [];
+        fromIterableSync([1], { closeIn: CloseMode.NEVER }).subscribe(
+            subscription({
+                next(x) {
+                    buf.push(x);
+                },
+            }),
+            map((x: number) => x + 10)
         );
         assert.deepEqual(buf, [11]);
     });