Add warning when importing "next" directly

[ijjk]

This ensures we warn when "next" is imported directly as this shouldn't be done.

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

x-ref: #35873

[ijjk]

Failing test suites

Commit: 97f3b3c

yarn testheadless test/integration/react-streaming-and-server-components/test/switchable-runtime.test.js

• Switchable runtime (prod) > should build /node-rsc-isr as an isr page with the nodejs runtime

Expand output

● Switchable runtime (prod) › should build /node-rsc-isr as an isr page with the nodejs runtime

expect(received).toBeLessThan(expected)

Expected: < 1649091109967
Received:   1649091109967

  114 |     expect(html3).toContain('Runtime: Node.js')
  115 |
> 116 |     expect(renderedAt2).toBeLessThan(renderedAt3)
      |                         ^
  117 |   })
  118 |
  119 |   it('should build /edge as a dynamic page with the edge runtime', async () => {

  at Object.<anonymous> (integration/react-streaming-and-server-components/test/switchable-runtime.test.js:116:25)

Read more about building and testing Next.js in contributing.md.

[styfle]

Thanks! I left a couple minor comments

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
buildDuration	16.1s	16.1s	⚠️ +12ms
buildDurationCached	6.1s	6.2s	⚠️ +39ms
nodeModulesSize	477 MB	477 MB	⚠️ +1.73 kB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.214	3.228	⚠️ +0.01
/ avg req/sec	777.94	774.48	⚠️ -3.46
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.425	1.453	⚠️ +0.03
/error-in-render avg req/sec	1754.86	1721.03	⚠️ -33.83

Client Bundles (main, webpack)

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
925.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	28.4 kB	28.4 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	72.1 kB	72.1 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
_app-HASH.js gzip	1.36 kB	1.36 kB	✓
_error-HASH.js gzip	192 B	192 B	✓
amp-HASH.js gzip	309 B	309 B	✓
css-HASH.js gzip	327 B	327 B	✓
dynamic-HASH.js gzip	3.05 kB	3.05 kB	✓
head-HASH.js gzip	351 B	351 B	✓
hooks-HASH.js gzip	920 B	920 B	✓
image-HASH.js gzip	5.52 kB	5.52 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.32 kB	2.32 kB	✓
routerDirect..HASH.js gzip	320 B	320 B	✓
script-HASH.js gzip	387 B	387 B	✓
withRouter-HASH.js gzip	319 B	319 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	15.7 kB	15.7 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
index.html gzip	532 B	532 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	525 B	525 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
buildDuration	18.9s	18.7s	-243ms
buildDurationCached	6.2s	6.1s	-43ms
nodeModulesSize	477 MB	477 MB	⚠️ +1.73 kB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.213	3.211	0
/ avg req/sec	778.21	778.5	+0.29
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.413	1.451	⚠️ +0.04
/error-in-render avg req/sec	1769.37	1722.64	⚠️ -46.73

Client Bundles (main, webpack)

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
925.HASH.js gzip	178 B	178 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.8 kB	28.8 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	72.7 kB	72.7 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	179 B	179 B	✓
amp-HASH.js gzip	313 B	313 B	✓
css-HASH.js gzip	325 B	325 B	✓
dynamic-HASH.js gzip	3.03 kB	3.03 kB	✓
head-HASH.js gzip	351 B	351 B	✓
hooks-HASH.js gzip	921 B	921 B	✓
image-HASH.js gzip	5.63 kB	5.63 kB	✓
index-HASH.js gzip	261 B	261 B	✓
link-HASH.js gzip	2.38 kB	2.38 kB	✓
routerDirect..HASH.js gzip	322 B	322 B	✓
script-HASH.js gzip	388 B	388 B	✓
withRouter-HASH.js gzip	317 B	317 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	15.9 kB	15.9 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	ijjk/next.js stub/next-import	Change
index.html gzip	531 B	531 B	✓
link.html gzip	544 B	544 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: bdd347a