Add warning for large number of routes

[ijjk]

This adds a warning when more than 1000 routes are added since it can have performance impacts and includes a document that we can add suggestions to reduce the number of routes being added.

Bug

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

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
buildDuration	12.4s	12.4s	⚠️ +39ms
buildDurationCached	2.9s	2.9s	-10ms
nodeModulesSize	49.4 MB	49.5 MB	⚠️ +1.73 kB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.097	2.077	-0.02
/ avg req/sec	1192.39	1203.44	+11.05
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.089	1.117	⚠️ +0.03
/error-in-render avg req/sec	2294.73	2238.9	⚠️ -55.83

Client Bundles (main, webpack, commons)

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
359.HASH.js gzip	2.96 kB	2.96 kB	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	20.9 kB	20.9 kB	✓
webpack-HASH.js gzip	1.49 kB	1.49 kB	✓
Overall change	67.4 kB	67.4 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
polyfills-HASH.js gzip	31.1 kB	31.1 kB	✓
Overall change	31.1 kB	31.1 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
_app-HASH.js gzip	803 B	803 B	✓
_error-HASH.js gzip	3.06 kB	3.06 kB	✓
amp-HASH.js gzip	554 B	554 B	✓
css-HASH.js gzip	329 B	329 B	✓
hooks-HASH.js gzip	903 B	903 B	✓
image-HASH.js gzip	5.6 kB	5.6 kB	✓
index-HASH.js gzip	261 B	261 B	✓
link-HASH.js gzip	1.66 kB	1.66 kB	✓
routerDirect..HASH.js gzip	319 B	319 B	✓
withRouter-HASH.js gzip	320 B	320 B	✓
bb14e60e810b..30f.css gzip	125 B	125 B	✓
Overall change	13.9 kB	13.9 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
_buildManifest.js gzip	417 B	417 B	✓
Overall change	417 B	417 B	✓

Rendered Page Sizes

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
index.html gzip	529 B	529 B	✓
link.html gzip	543 B	543 B	✓
withRouter.html gzip	523 B	523 B	✓
Overall change	1.59 kB	1.59 kB	✓

---

Webpack 4 Mode (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
buildDuration	9.9s	9.9s	-9ms
buildDurationCached	4s	3.9s	-110ms
nodeModulesSize	49.4 MB	49.5 MB	⚠️ +1.73 kB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.11	2.096	-0.01
/ avg req/sec	1184.84	1192.68	+7.84
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.087	1.119	⚠️ +0.03
/error-in-render avg req/sec	2299.98	2234.09	⚠️ -65.89

Client Bundles (main, webpack, commons)

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
14.HASH.js gzip	2.98 kB	2.98 kB	✓
677f882d2ed8..HASH.js gzip	13.7 kB	13.7 kB	✓
framework.HASH.js gzip	41.8 kB	41.8 kB	✓
main-HASH.js gzip	8.39 kB	8.39 kB	✓
webpack-HASH.js gzip	1.19 kB	1.19 kB	✓
Overall change	68 kB	68 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
polyfills-HASH.js gzip	31.3 kB	31.3 kB	✓
Overall change	31.3 kB	31.3 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
_app-HASH.js gzip	791 B	791 B	✓
_error-HASH.js gzip	3.76 kB	3.76 kB	✓
amp-HASH.js gzip	552 B	552 B	✓
css-HASH.js gzip	333 B	333 B	✓
hooks-HASH.js gzip	910 B	910 B	✓
index-HASH.js gzip	230 B	230 B	✓
link-HASH.js gzip	1.64 kB	1.64 kB	✓
routerDirect..HASH.js gzip	297 B	297 B	✓
withRouter-HASH.js gzip	293 B	293 B	✓
e025d2764813..52f.css gzip	125 B	125 B	✓
Overall change	8.93 kB	8.93 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
_buildManifest.js gzip	420 B	420 B	✓
Overall change	420 B	420 B	✓

Rendered Page Sizes

	vercel/next.js canary	ijjk/next.js add/routes-amount-warning	Change
index.html gzip	576 B	576 B	✓
link.html gzip	590 B	590 B	✓
withRouter.html gzip	569 B	569 B	✓
Overall change	1.74 kB	1.74 kB	✓

Commit: d35b08f