Fix middleware i18n rewrites

[javivelasco]

Fixes #30897

This PR fixes the linked issue where rewrites are not being applied for locale. It adds the corresponding test but also, as it was added in debugging process, it introduces a helper to read/write into the request object.

We are currently writing directly into the request by casting to any and then using flags like _nextRewrote. Instead, this PR puts all of this metadata under a symbol so it is not directly accessible. This also allows to have a single place where all of this metadata is listed so we can add comments describing the purpose of each flag.

In the same way, there is metadata written in the querystring. This is adding some types for it in order to throw some visibility on where is this metadata accessed. In an upcoming PR we can move all of it to the request object if possible to simplify the system.

Bug

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

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
buildDuration	17.7s	17.6s	-73ms
buildDurationCached	3.6s	3.6s	-14ms
nodeModulesSize	332 MB	332 MB	⚠️ +3.89 kB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.913	2.921	⚠️ +0.01
/ avg req/sec	858.22	855.94	⚠️ -2.28
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.315	1.403	⚠️ +0.09
/error-in-render avg req/sec	1901.81	1781.39	⚠️ -120.42

Client Bundles (main, webpack, commons)

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	28.1 kB	28.1 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	71.9 kB	71.9 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
_app-HASH.js gzip	1.23 kB	1.23 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	327 B	327 B	✓
dynamic-HASH.js gzip	2.38 kB	2.38 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	635 B	635 B	✓
image-HASH.js gzip	4.44 kB	4.44 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	1.87 kB	1.87 kB	✓
routerDirect..HASH.js gzip	321 B	321 B	✓
script-HASH.js gzip	383 B	383 B	✓
withRouter-HASH.js gzip	318 B	318 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	13.1 kB	13.1 kB	✓

Client Build Manifests

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
index.html gzip	523 B	523 B	✓
link.html gzip	536 B	536 B	✓
withRouter.html gzip	518 B	518 B	✓
Overall change	1.58 kB	1.58 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
buildDuration	19.1s	19.3s	⚠️ +281ms
buildDurationCached	3.6s	3.6s	⚠️ +15ms
nodeModulesSize	332 MB	332 MB	⚠️ +3.89 kB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.915	2.925	⚠️ +0.01
/ avg req/sec	857.53	854.8	⚠️ -2.73
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.361	1.379	⚠️ +0.02
/error-in-render avg req/sec	1836.6	1813.55	⚠️ -23.05

Client Bundles (main, webpack, commons)

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.2 kB	28.2 kB	✓
webpack-HASH.js gzip	1.43 kB	1.43 kB	✓
Overall change	72.1 kB	72.1 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
_app-HASH.js gzip	1.22 kB	1.22 kB	✓
_error-HASH.js gzip	180 B	180 B	✓
amp-HASH.js gzip	305 B	305 B	✓
css-HASH.js gzip	321 B	321 B	✓
dynamic-HASH.js gzip	2.38 kB	2.38 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	622 B	622 B	✓
image-HASH.js gzip	4.46 kB	4.46 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	1.91 kB	1.91 kB	✓
routerDirect..HASH.js gzip	314 B	314 B	✓
script-HASH.js gzip	375 B	375 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	13.1 kB	13.1 kB	✓

Client Build Manifests

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	javivelasco/next.js fix/middleware-i18n-rewrites	Change
index.html gzip	523 B	523 B	✓
link.html gzip	535 B	535 B	✓
withRouter.html gzip	517 B	517 B	✓
Overall change	1.57 kB	1.57 kB	✓

Commit: c7ff9d4