From 2a1a729e8e17c56c11fec9e2d694cc64ab2da695 Mon Sep 17 00:00:00 2001
From: Steven Luscher <steveluscher@users.noreply.github.com>
Date: Wed, 21 Aug 2024 13:52:26 -0700
Subject: [PATCH] The subscriptions coalescer now publishes the final message
 of the inner iterator (#3132)

# Summary

What if a custom transport _returns_ its final value? Before this PR, the coalescer would not deliver the final message, if the `done` property and the `value` came in the same iteration.
---
 .../rpc-subscriptions-coalescer-test.ts         | 17 ++++++++++++++++-
 .../src/rpc-subscriptions-coalescer.ts          |  2 +-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/packages/rpc-subscriptions/src/__tests__/rpc-subscriptions-coalescer-test.ts b/packages/rpc-subscriptions/src/__tests__/rpc-subscriptions-coalescer-test.ts
index f88dbce1855b..87ca87c3d77c 100644
--- a/packages/rpc-subscriptions/src/__tests__/rpc-subscriptions-coalescer-test.ts
+++ b/packages/rpc-subscriptions/src/__tests__/rpc-subscriptions-coalescer-test.ts
@@ -8,7 +8,7 @@ interface TestRpcSubscriptionNotifications {
 }
 
 describe('getRpcSubscriptionsWithSubscriptionCoalescing', () => {
-    let asyncGenerator: jest.Mock<AsyncGenerator<unknown, void>>;
+    let asyncGenerator: jest.Mock<AsyncGenerator<unknown, unknown>>;
     let createPendingSubscription: jest.Mock;
     let getDeduplicationKey: jest.Mock;
     let subscribe: jest.Mock;
@@ -115,6 +115,21 @@ describe('getRpcSubscriptionsWithSubscriptionCoalescing', () => {
             await expect(messagePromiseA).resolves.toHaveProperty('value', 'hello');
             await expect(messagePromiseB).resolves.toHaveProperty('value', 'hello');
         });
+        it('publishes the final message when the iterable returns', async () => {
+            expect.assertions(1);
+            asyncGenerator.mockImplementation(
+                // eslint-disable-next-line require-yield
+                async function* () {
+                    return await Promise.resolve('hello');
+                },
+            );
+            const iterable = await rpcSubscriptions
+                .thingNotifications({ payload: 'hello' })
+                .subscribe({ abortSignal: new AbortController().signal });
+            const iterator = iterable[Symbol.asyncIterator]();
+            const messagePromise = iterator.next();
+            await expect(messagePromise).resolves.toHaveProperty('value', 'hello');
+        });
         it('aborting a subscription causes it to return', async () => {
             expect.assertions(1);
             asyncGenerator.mockImplementation(async function* () {
diff --git a/packages/rpc-subscriptions/src/rpc-subscriptions-coalescer.ts b/packages/rpc-subscriptions/src/rpc-subscriptions-coalescer.ts
index 1de90850b09e..bfcf66fa3448 100644
--- a/packages/rpc-subscriptions/src/rpc-subscriptions-coalescer.ts
+++ b/packages/rpc-subscriptions/src/rpc-subscriptions-coalescer.ts
@@ -108,7 +108,7 @@ export function getRpcSubscriptionsWithSubscriptionCoalescing<TRpcSubscriptionsM
                                     while (true) {
                                         const iteratorResult = await safeRace([iterator.next(), abortPromise]);
                                         if (iteratorResult.done) {
-                                            return;
+                                            return iteratorResult.value;
                                         } else {
                                             yield iteratorResult.value;
                                         }