Turbopack server hmr: extract core hmr client logic #88912

wbinnssmith · 2026-01-22T20:26:36Z

This PR mostly moves existing code.

This extracts the core HMR client logic, abstracting away hooks for platform-specific features like the websocket transport and page reload.

In a future PR this will be implemented as an in-process backend for nodejs server hmr.

Test Plan: CI, existing hmr tests

wbinnssmith · 2026-01-22T20:26:53Z

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Turbopack server hmr: extract core hmr client logic #88912 👈 (View in Graphite)
Server HMR infrastructure #88870
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nextjs-bot · 2026-01-22T20:36:43Z

Failing test suites

Commit: a8262a5 | About building and testing Next.js

pnpm test-start-turbo test/e2e/app-dir/app-client-cache/client-cache.parallel-routes.test.ts (turbopack) (job)

app dir client cache with parallel routes > prefetch={true} > should prefetch the full page (DD)

Expand output

● app dir client cache with parallel routes › prefetch={true} › should prefetch the full page

thrown: "Exceeded timeout of 120000 ms for a test.
Add a timeout value to this test to increase the timeout, if this is a long-running test. See https://jestjs.io/docs/api#testname-fn-timeout."

  29 |
  30 |   describe('prefetch={true}', () => {
> 31 |     it('should prefetch the full page', async () => {
     |     ^
  32 |       let page: PlaywrightPage
  33 |       const browser = await next.browser('/', {
  34 |         async beforePageLoad(p) {

  at it (e2e/app-dir/app-client-cache/client-cache.parallel-routes.test.ts:31:5)
  at describe (e2e/app-dir/app-client-cache/client-cache.parallel-routes.test.ts:30:3)
  at Object.describe (e2e/app-dir/app-client-cache/client-cache.parallel-routes.test.ts:7:1)

pnpm test-start test/e2e/app-dir/segment-cache/prefetch-runtime/prefetch-runtime.test.ts (job)

runtime prefetching > in a private cache > includes dynamic params, but not dynamic content (DD)

Expand output

● runtime prefetching › in a private cache › includes dynamic params, but not dynamic content

thrown: "Exceeded timeout of 120000 ms for a test.
Add a timeout value to this test to increase the timeout, if this is a long-running test. See https://jestjs.io/docs/api#testname-fn-timeout."

  44 |     },
  45 |   ])('$description', ({ prefix }) => {
> 46 |     it('includes dynamic params, but not dynamic content', async () => {
     |     ^
  47 |       let page: Playwright.Page
  48 |       const browser = await next.browser('/', {
  49 |         beforePageLoad(p: Playwright.Page) {

  at it (e2e/app-dir/segment-cache/prefetch-runtime/prefetch-runtime.test.ts:46:5)
      at Array.forEach (<anonymous>)
  at e2e/app-dir/segment-cache/prefetch-runtime/prefetch-runtime.test.ts:45:4
  at Object.describe (e2e/app-dir/segment-cache/prefetch-runtime/prefetch-runtime.test.ts:6:1)

codspeed-hq · 2026-01-22T20:37:10Z

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing wbinnssmith/server-hmr-runtime-refactor (0c9c18d) with wbinnssmith/server-hmr-runtime-mvp (36882f9)}

Summary

✅ 17 untouched benchmarks
⏩ 3 skipped benchmarks¹

3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

vercel

Additional Suggestion:

Import statement references non-existent type WebSocketMessage instead of the renamed HmrMessage type

nextjs-bot · 2026-01-22T21:38:33Z

Stats from current PR

🔴 1 regression

Metric	Canary	PR	Change	Trend
node_modules Size	461 MB	461 MB	🔴 +46.9 kB (+0%)	▁▁▁▁▁

📊 All Metrics

📖 Metrics Glossary

Dev Server Metrics:

Listen = TCP port starts accepting connections
First Request = HTTP server returns successful response
Cold = Fresh build (no cache)
Warm = With cached build artifacts

Build Metrics:

Fresh = Clean build (no .next directory)
Cached = With existing .next directory

Change Thresholds:

Time: Changes < 50ms AND < 10%, OR < 2% are insignificant
Size: Changes < 1KB AND < 1% are insignificant
All other changes are flagged to catch regressions

⚡ Dev Server

Metric	Canary	PR	Change	Trend
Cold (Listen)	456ms	455ms	✓	▁▁▁▁▁
Cold (Ready in log)	440ms	439ms	✓	▁▁▁▁▁
Cold (First Request)	1.177s	1.182s	✓	▁▃▃▃▁
Warm (Listen)	456ms	457ms	✓	▂▁▁▁▁
Warm (Ready in log)	442ms	442ms	✓	▁▁▁▁▁
Warm (First Request)	338ms	363ms	✓	▂▂▂▁▁

📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric	Canary	PR	Change	Trend
Cold (Listen)	455ms	455ms	✓	▁▁▁▁▁
Cold (Ready in log)	433ms	435ms	✓	▁▁▁▁▁
Cold (First Request)	1.806s	1.820s	✓	▁▁▁▁▁
Warm (Listen)	456ms	455ms	✓	▁▁▁▁▁
Warm (Ready in log)	435ms	434ms	✓	▁▁▁▁▁
Warm (First Request)	1.818s	1.820s	✓	▁▁▁▁▁

⚡ Production Builds

Metric	Canary	PR	Change	Trend
Fresh Build	4.310s	4.311s	✓	▂▁▁▁▂
Cached Build	4.287s	4.279s	✓	▁▁▁▁▁

📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric	Canary	PR	Change	Trend
Fresh Build	13.943s	13.981s	✓	▃▃▄▃▃
Cached Build	14.105s	14.113s	✓	▂▁▃▃▂
node_modules Size	461 MB	461 MB	🔴 +46.9 kB (+0%)	▁▁▁▁▁

📦 Bundle Sizes

Bundle Sizes

⚡ Turbopack

Client

Main Bundles: **432 kB** → **432 kB** ✅ -32 B

82 files with content-based hashes (individual files not comparable between builds)

Server

Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	762 B	768 B	✓
Total	762 B	768 B	⚠️ +6 B

Build Details

Build Manifests

	Canary	PR	Change
_buildManifest.js gzip	450 B	451 B	✓
Total	450 B	451 B	⚠️ +1 B

📦 Webpack

Client

Main Bundles

	Canary	PR	Change
2086.HASH.js gzip	169 B	N/A	-
2161-HASH.js gzip	5.41 kB	N/A	-
2747-HASH.js gzip	4.48 kB	N/A	-
4322-HASH.js gzip	52.7 kB	N/A	-
ec793fe8-HASH.js gzip	62.3 kB	N/A	-
framework-HASH.js gzip	59.8 kB	59.8 kB	✓
main-app-HASH.js gzip	251 B	254 B	🔴 +3 B (+1%)
main-HASH.js gzip	38.7 kB	39.1 kB	✓
webpack-HASH.js gzip	1.68 kB	1.68 kB	✓
1596.HASH.js gzip	N/A	169 B	-
2658-HASH.js gzip	N/A	52.4 kB	-
6349-HASH.js gzip	N/A	4.46 kB	-
7019-HASH.js gzip	N/A	5.43 kB	-
b17a3386-HASH.js gzip	N/A	62.3 kB	-
Total	226 kB	226 kB	⚠️ +55 B

Polyfills

	Canary	PR	Change
polyfills-HASH.js gzip	39.4 kB	39.4 kB	✓
Total	39.4 kB	39.4 kB	✓

Pages

	Canary	PR	Change
_app-HASH.js gzip	194 B	193 B	✓
_error-HASH.js gzip	182 B	182 B	✓
css-HASH.js gzip	336 B	335 B	✓
dynamic-HASH.js gzip	1.8 kB	1.8 kB	✓
edge-ssr-HASH.js gzip	256 B	256 B	✓
head-HASH.js gzip	352 B	349 B	✓
hooks-HASH.js gzip	385 B	384 B	✓
image-HASH.js gzip	580 B	580 B	✓
index-HASH.js gzip	259 B	258 B	✓
link-HASH.js gzip	2.5 kB	2.51 kB	✓
routerDirect..HASH.js gzip	319 B	317 B	✓
script-HASH.js gzip	385 B	387 B	✓
withRouter-HASH.js gzip	316 B	315 B	✓
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Total	7.97 kB	7.96 kB	✅ -8 B

Server

Edge SSR

	Canary	PR	Change
edge-ssr.js gzip	126 kB	126 kB	✓
page.js gzip	244 kB	240 kB	🟢 4.5 kB (-2%)
Total	371 kB	366 kB	✅ -4.63 kB

Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	618 B	618 B	✓
middleware-r..fest.js gzip	155 B	156 B	✓
middleware.js gzip	33.1 kB	33.3 kB	✓
edge-runtime..pack.js gzip	842 B	842 B	✓
Total	34.7 kB	34.9 kB	⚠️ +168 B

Build Details

Build Manifests

	Canary	PR	Change
_buildManifest.js gzip	738 B	738 B	✓
Total	738 B	738 B	✓

Build Cache

	Canary	PR	Change
0.pack gzip	3.71 MB	3.72 MB	🔴 +13.4 kB (+0%)
index.pack gzip	103 kB	100 kB	🟢 2.1 kB (-2%)
index.pack.old gzip	102 kB	102 kB	✓
Total	3.92 MB	3.93 MB	⚠️ +10.8 kB

🔄 Shared (bundler-independent)

Runtimes

	Canary	PR	Change
app-page-exp...dev.js gzip	306 kB	306 kB	✓
app-page-exp..prod.js gzip	163 kB	163 kB	✓
app-page-tur...dev.js gzip	306 kB	306 kB	✓
app-page-tur..prod.js gzip	163 kB	163 kB	✓
app-page-tur...dev.js gzip	303 kB	303 kB	✓
app-page-tur..prod.js gzip	161 kB	161 kB	✓
app-page.run...dev.js gzip	303 kB	303 kB	✓
app-page.run..prod.js gzip	161 kB	161 kB	✓
app-route-ex...dev.js gzip	69.4 kB	69.4 kB	✓
app-route-ex..prod.js gzip	48.2 kB	48.2 kB	✓
app-route-tu...dev.js gzip	69.5 kB	69.5 kB	✓
app-route-tu..prod.js gzip	48.2 kB	48.2 kB	✓
app-route-tu...dev.js gzip	69.1 kB	69.1 kB	✓
app-route-tu..prod.js gzip	48 kB	48 kB	✓
app-route.ru...dev.js gzip	69 kB	69 kB	✓
app-route.ru..prod.js gzip	48 kB	48 kB	✓
dist_client_...dev.js gzip	324 B	324 B	✓
dist_client_...dev.js gzip	326 B	326 B	✓
dist_client_...dev.js gzip	318 B	318 B	✓
dist_client_...dev.js gzip	317 B	317 B	✓
pages-api-tu...dev.js gzip	42.5 kB	42.5 kB	✓
pages-api-tu..prod.js gzip	32.3 kB	32.3 kB	✓
pages-api.ru...dev.js gzip	42.5 kB	42.5 kB	✓
pages-api.ru..prod.js gzip	32.3 kB	32.3 kB	✓
pages-turbo....dev.js gzip	51.8 kB	51.8 kB	✓
pages-turbo...prod.js gzip	38.8 kB	38.8 kB	✓
pages.runtim...dev.js gzip	51.8 kB	51.8 kB	✓
pages.runtim..prod.js gzip	38.8 kB	38.8 kB	✓
server.runti..prod.js gzip	62.3 kB	62.3 kB	✓
Total	2.73 MB	2.73 MB	✅ -3 B

This extracts the core HMR client logic, abstracting away hooks for platform-specific features like the websocket transport and page reload. In a future PR this will be implemented as an in-process backend for nodejs server hmr. Test Plan: CI, existing hmr tests

nextjs-bot added created-by: Turbopack team PRs by the Turbopack team. Turbopack Related to Turbopack with Next.js. labels Jan 22, 2026

wbinnssmith mentioned this pull request Jan 22, 2026

Server HMR infrastructure #88870

Open

wbinnssmith marked this pull request as ready for review January 22, 2026 20:27

wbinnssmith force-pushed the wbinnssmith/server-hmr-runtime-refactor branch from 65424d5 to 98149b4 Compare January 22, 2026 20:35

vercel bot reviewed Jan 22, 2026

View reviewed changes

wbinnssmith force-pushed the wbinnssmith/server-hmr-runtime-refactor branch from 98149b4 to 4bea106 Compare January 22, 2026 21:14

wbinnssmith force-pushed the wbinnssmith/server-hmr-runtime-mvp branch from 278d39f to 392acd5 Compare January 22, 2026 21:14

wbinnssmith force-pushed the wbinnssmith/server-hmr-runtime-refactor branch from 4bea106 to b77b14c Compare January 22, 2026 21:59

wbinnssmith changed the base branch from wbinnssmith/server-hmr-runtime-mvp to graphite-base/88912 January 22, 2026 23:13

wbinnssmith force-pushed the wbinnssmith/server-hmr-runtime-refactor branch from b77b14c to a8262a5 Compare January 22, 2026 23:15

wbinnssmith force-pushed the graphite-base/88912 branch from 0e13692 to 36882f9 Compare January 22, 2026 23:15

wbinnssmith changed the base branch from graphite-base/88912 to wbinnssmith/server-hmr-runtime-mvp January 22, 2026 23:15

wbinnssmith force-pushed the wbinnssmith/server-hmr-runtime-refactor branch from a8262a5 to 0c9c18d Compare January 23, 2026 00:07

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Turbopack server hmr: extract core hmr client logic #88912

Turbopack server hmr: extract core hmr client logic #88912

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