From c250b7d980864be49facf2306f06455e7f9e305d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Markb=C3=A5ge?= <sebastian@calyptus.eu>
Date: Fri, 16 May 2025 14:53:40 -0400
Subject: [PATCH] [Fizz] Should be considered complete inside onShellReady
 callback (#33295)

We decremented `allPendingTasks` after invoking `onShellReady`. Which
means that in that scope it wasn't considered fully complete.

Since the pattern for flushing in Node.js is to start piping in
`onShellReady` and that's how you can get sync behavior, this led us to
think that we had more work left to do. For example we emitted the
`writeShellTimeInstruction` in this scenario before.
---
 .../src/__tests__/ReactDOMFizzServerNode-test.js  | 15 +++++++++++++++
 packages/react-server/src/ReactFizzServer.js      |  2 +-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/packages/react-dom/src/__tests__/ReactDOMFizzServerNode-test.js b/packages/react-dom/src/__tests__/ReactDOMFizzServerNode-test.js
index d4f3486a1db..198ccb4f8f6 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFizzServerNode-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFizzServerNode-test.js
@@ -67,6 +67,21 @@ describe('ReactDOMFizzServerNode', () => {
     expect(output.result).toMatchInlineSnapshot(`"<div>hello world</div>"`);
   });
 
+  it('flush fully if piping in on onShellReady', async () => {
+    const {writable, output} = getTestWritable();
+    await act(() => {
+      const {pipe} = ReactDOMFizzServer.renderToPipeableStream(
+        <div>hello world</div>,
+        {
+          onShellReady() {
+            pipe(writable);
+          },
+        },
+      );
+    });
+    expect(output.result).toMatchInlineSnapshot(`"<div>hello world</div>"`);
+  });
+
   it('should emit DOCTYPE at the root of the document', async () => {
     const {writable, output} = getTestWritable();
     await act(() => {
diff --git a/packages/react-server/src/ReactFizzServer.js b/packages/react-server/src/ReactFizzServer.js
index a0388968e82..a159771421b 100644
--- a/packages/react-server/src/ReactFizzServer.js
+++ b/packages/react-server/src/ReactFizzServer.js
@@ -4335,6 +4335,7 @@ function finishedTask(
   boundary: Root | SuspenseBoundary,
   segment: null | Segment,
 ) {
+  request.allPendingTasks--;
   if (boundary === null) {
     if (segment !== null && segment.parentFlushed) {
       if (request.completedRootSegment !== null) {
@@ -4417,7 +4418,6 @@ function finishedTask(
     }
   }
 
-  request.allPendingTasks--;
   if (request.allPendingTasks === 0) {
     completeAll(request);
   }