[edge] serialize custom config to middleware-manifest (#40881)

This PR serializes `regions` into `middleware-manifest.json`,
allowing to extend Edge Functions and Middleware for deployment
providers.

## 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 a helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

Co-authored-by: Seiya Nuta <nuta@seiya.me>
Co-authored-by: JJ Kasper <jj@jjsweb.site>

packages/next/build/analysis/get-page-static-info.ts

@@ -18,6 +18,7 @@ import { RSC_MODULE_TYPES } from '../../shared/lib/constants'
 export interface MiddlewareConfig {
   matchers: MiddlewareMatcher[]
   unstable_allowDynamicGlobs: string[]
+  regions: string[] | string
 }
 
 export interface MiddlewareMatcher {
@@ -184,6 +185,14 @@ function getMiddlewareConfig(
     result.matchers = getMiddlewareMatchers(config.matcher, nextConfig)
   }
 
+  if (typeof config.regions === 'string' || Array.isArray(config.regions)) {
+    result.regions = config.regions
+  } else if (typeof config.regions !== 'undefined') {
+    Log.warn(
+      `The \`regions\` config was ignored: config must be empty, a string or an array of strings. (${pageFilePath})`
+    )
+  }
+
   if (config.unstable_allowDynamic) {
     result.unstable_allowDynamicGlobs = Array.isArray(
       config.unstable_allowDynamic
@@ -256,7 +265,7 @@ export async function getPageStaticInfo(params: {
 
   const fileContent = (await tryToReadFile(pageFilePath, !isDev)) || ''
   if (
-    /runtime|getStaticProps|getServerSideProps|matcher|unstable_allowDynamic/.test(
+    /runtime|getStaticProps|getServerSideProps|export const config/.test(
       fileContent
     )
   ) {

packages/next/build/webpack/plugins/middleware-plugin.ts

@@ -36,6 +36,7 @@ export interface EdgeFunctionDefinition {
   matchers: MiddlewareMatcher[]
   wasm?: AssetBinding[]
   assets?: AssetBinding[]
+  regions?: string[] | string
 }
 
 export interface MiddlewareManifest {
@@ -52,6 +53,7 @@ interface EntryMetadata {
   env: Set<string>
   wasmBindings: Map<string, string>
   assetBindings: Map<string, string>
+  regions?: string[] | string
 }
 
 const NAME = 'MiddlewarePlugin'
@@ -178,6 +180,7 @@ function getCreateAssets(params: {
           name,
           filePath,
         })),
+        ...(metadata.regions && { regions: metadata.regions }),
       }
 
       if (metadata.edgeApiFunction || metadata.edgeSSR) {
@@ -737,6 +740,10 @@ function getExtractMetadata(params: {
           }
         }
 
+        if (edgeFunctionConfig?.config?.regions) {
+          entryMetadata.regions = edgeFunctionConfig.config.regions
+        }
+
         /**
          * The entry module has to be either a page or a middleware and hold
          * the corresponding metadata.

test/e2e/middleware-general/app/middleware.js

@@ -2,6 +2,8 @@
 import { NextRequest, NextResponse, URLPattern } from 'next/server'
 import magicValue from 'shared-package'
 
+export const config = { regions: 'auto' }
+
 const PATTERNS = [
   [
     new URLPattern({ pathname: '/:locale/:id' }),

test/e2e/middleware-general/app/pages/api/edge-search-params.js

@@ -1,6 +1,6 @@
 import { NextResponse } from 'next/server'
 
-export const config = { runtime: 'experimental-edge' }
+export const config = { runtime: 'experimental-edge', regions: 'default' }
 
 /**
  * @param {import('next/server').NextRequest}

test/e2e/middleware-general/test/index.test.ts

@@ -125,10 +125,22 @@ describe('Middleware Runtime', () => {
             matchers: [{ regexp: '^/.*$' }],
             wasm: [],
             assets: [],
+            regions: 'auto',
           },
         })
       })
 
+      it('should have the custom config in the manifest', async () => {
+        const manifest = await fs.readJSON(
+          join(next.testDir, '.next/server/middleware-manifest.json')
+        )
+
+        expect(manifest.functions['/api/edge-search-params']).toHaveProperty(
+          'regions',
+          'default'
+        )
+      })
+
       it('should have correct files in manifest', async () => {
         const manifest = await fs.readJSON(
           join(next.testDir, '.next/server/middleware-manifest.json')