Add TS types for NextMiddleware

[styfle]

This allows TypeScript users to have type safety for middleware functions.

• Closes docs: add NextResponse to the Middleware function signature #30490

[ijjk]

Can we convert one of the _middleware in the middleware-core tests to use these types so we can ensure they are working correctly?

Added TS tests

[molebox]

This looks fine to me

[ijjk]

Failing test suites

Commit: 2f5f985

test/integration/middleware-typescript/test/index.test.js

• TypeScript Middleware > next build > should not fail to build middleware

Expand output

● TypeScript Middleware › next build › should not fail to build middleware

expect(received).not.toMatch(expected)

Expected pattern: not /Failed to compile/
Received string:      "Failed to compile.

../../../packages/next/build/compiler.ts:39:19
Type error: Namespace '\"/home/runner/work/next.js/next.js/packages/next/dist/compiled/webpack/webpack\".webpack' has no exported member 'Configuration'.

  37 | 
  38 | export function runCompiler(
> 39 |   config: webpack.Configuration,
     |                   ^
  40 |   { runWebpackSpan }: { runWebpackSpan: Span }
  41 | ): Promise<CompilerResult> {
  42 |   return new Promise((resolve, reject) => {
"

   9 |     it('should not fail to build middleware', async () => {
  10 |       const { stderr, code } = await nextBuild(appDir, [], { stderr: true })
> 11 |       expect(stderr).not.toMatch(/Failed to compile/)
     |                                ^
  12 |       expect(stderr).not.toMatch(/is not assignable to type/)
  13 |       expect(code).toBe(0)
  14 |     })

  at Object.<anonymous> (integration/middleware-typescript/test/index.test.js:11:32)

[molebox]

Can we convert one of the _middleware in the middleware-core tests to use these types so we can ensure they are working correctly?

Hey @ijjk do you know if this was done? If so, and you're happy, lets ship!

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
buildDuration	22.4s	22.9s	⚠️ +454ms
buildDurationCached	4.1s	4.2s	⚠️ +128ms
nodeModulesSize	347 MB	347 MB	⚠️ +409 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.534	3.752	⚠️ +0.22
/ avg req/sec	707.37	666.39	⚠️ -40.98
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.878	1.834	-0.04
/error-in-render avg req/sec	1331.5	1363.42	+31.92

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	28.4 kB	28.4 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	72.3 kB	72.3 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
_app-HASH.js gzip	1.37 kB	1.37 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	326 B	326 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	4.49 kB	4.49 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	13.3 kB	13.3 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
index.html gzip	532 B	532 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
buildDuration	23.3s	23.6s	⚠️ +302ms
buildDurationCached	3.9s	4s	⚠️ +154ms
nodeModulesSize	347 MB	347 MB	⚠️ +409 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.503	3.606	⚠️ +0.1
/ avg req/sec	713.72	693.33	⚠️ -20.39
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.637	1.762	⚠️ +0.13
/error-in-render avg req/sec	1527.53	1418.97	⚠️ -108.56

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.6 kB	28.6 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	72.5 kB	72.5 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
_app-HASH.js gzip	1.35 kB	1.35 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	2.37 kB	2.37 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	622 B	622 B	✓
image-HASH.js gzip	4.53 kB	4.53 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	13.3 kB	13.3 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
_buildManifest.js gzip	458 B	458 B	✓
Overall change	458 B	458 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js add-types-for-next-middleware	Change
index.html gzip	532 B	532 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: aedf68c