feat(ts): expose MiddlewareConfig interface

[balazsorban44]

What?

Expose the MiddlewareConfig interface.

Why?

You can now import type { MiddlewareConfig } from "next/server" to type the config object in your middleware.ts file.

Now you an type the entire file for example like so:

// middleware.ts
import type { NextMiddleware, MiddlewareConfig } from "next/server"

export const middleware: NextMiddleware = async (req) => {
  //...
}

export const config: MiddlewareConfig = {
  //...
}

How?

Re-exported the interface from its current location via server/web/types, to colocate it with NextMidldeware.

I wonder if we could somehow type this file automatically, but it might be dependent on microsoft/TypeScript#38511

Closes NEXT-2308

Slack thread, Slack thread

[ijjk]

Tests Passed

[ijjk]

Stats from current PR

Default Build

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js fix/expose-middleware-config-type	Change
buildDuration	11.6s	11.6s	N/A
buildDurationCached	5.9s	4.8s	N/A
nodeModulesSize	200 MB	200 MB	⚠️ +1.44 kB
nextStartRea..uration (ms)	425ms	432ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js fix/expose-middleware-config-type	Change
3f784ff6-HASH.js gzip	53.4 kB	53.4 kB	✓
423.HASH.js gzip	185 B	181 B	N/A
68-HASH.js gzip	29.8 kB	29.9 kB	N/A
framework-HASH.js gzip	45.2 kB	45.2 kB	✓
main-app-HASH.js gzip	238 B	239 B	N/A
main-HASH.js gzip	31.8 kB	31.8 kB	N/A
webpack-HASH.js gzip	1.7 kB	1.7 kB	✓
Overall change	100 kB	100 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js fix/expose-middleware-config-type	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js fix/expose-middleware-config-type	Change
_app-HASH.js gzip	194 B	195 B	N/A
_error-HASH.js gzip	182 B	181 B	N/A
amp-HASH.js gzip	502 B	502 B	✓
css-HASH.js gzip	320 B	322 B	N/A
dynamic-HASH.js gzip	2.5 kB	2.5 kB	N/A
edge-ssr-HASH.js gzip	255 B	256 B	N/A
head-HASH.js gzip	350 B	349 B	N/A
hooks-HASH.js gzip	368 B	369 B	N/A
image-HASH.js gzip	4.18 kB	4.18 kB	N/A
index-HASH.js gzip	257 B	256 B	N/A
link-HASH.js gzip	2.61 kB	2.61 kB	N/A
routerDirect..HASH.js gzip	310 B	311 B	N/A
script-HASH.js gzip	384 B	383 B	N/A
withRouter-HASH.js gzip	306 B	308 B	N/A
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	608 B	608 B	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js fix/expose-middleware-config-type	Change
_buildManifest.js gzip	484 B	484 B	✓
Overall change	484 B	484 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js fix/expose-middleware-config-type	Change
index.html gzip	528 B	527 B	N/A
link.html gzip	541 B	540 B	N/A
withRouter.html gzip	523 B	522 B	N/A
Overall change	0 B	0 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js fix/expose-middleware-config-type	Change
edge-ssr.js gzip	94 kB	94 kB	N/A
page.js gzip	150 kB	150 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js fix/expose-middleware-config-type	Change
middleware-b..fest.js gzip	626 B	622 B	N/A
middleware-r..fest.js gzip	151 B	149 B	N/A
middleware.js gzip	37.6 kB	37.6 kB	N/A
edge-runtime..pack.js gzip	1.92 kB	1.92 kB	✓
Overall change	1.92 kB	1.92 kB	✓

Next Runtimes

	vercel/next.js canary	vercel/next.js fix/expose-middleware-config-type	Change
app-page-exp...dev.js gzip	170 kB	170 kB	✓
app-page-exp..prod.js gzip	95.8 kB	95.8 kB	✓
app-page-tur..prod.js gzip	96.4 kB	96.4 kB	✓
app-page-tur..prod.js gzip	91 kB	91 kB	✓
app-page.run...dev.js gzip	142 kB	142 kB	✓
app-page.run..prod.js gzip	90.3 kB	90.3 kB	✓
app-route-ex...dev.js gzip	22.2 kB	22.2 kB	✓
app-route-ex..prod.js gzip	14.9 kB	14.9 kB	✓
app-route-tu..prod.js gzip	14.9 kB	14.9 kB	✓
app-route-tu..prod.js gzip	14.5 kB	14.5 kB	✓
app-route.ru...dev.js gzip	21.7 kB	21.7 kB	✓
app-route.ru..prod.js gzip	14.5 kB	14.5 kB	✓
pages-api-tu..prod.js gzip	9.43 kB	9.43 kB	✓
pages-api.ru...dev.js gzip	9.7 kB	9.7 kB	✓
pages-api.ru..prod.js gzip	9.43 kB	9.43 kB	✓
pages-turbo...prod.js gzip	22 kB	22 kB	✓
pages.runtim...dev.js gzip	22.7 kB	22.7 kB	✓
pages.runtim..prod.js gzip	22 kB	22 kB	✓
server.runti..prod.js gzip	49.7 kB	49.7 kB	N/A
Overall change	884 kB	884 kB	✓

Diff details

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Diff for edge-ssr.js

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Diff for 68-HASH.js

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Diff for server.runtime.prod.js

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Commit: f1a8b15

[ijjk]

Can we add a basic test for this type in https://github.com/vercel/next.js/blob/canary/test/production/middleware-typescript/app/middleware.ts?

[juliusmarminge]

Is this type correct? It doesn't match the docs where we can have a matcher: string attribute: https://nextjs.org/docs/app/building-your-application/routing/middleware#example