Generate functions manifest (#33770)

## Feature

Reuse most of the part from manifest plugin to generate similar assets

Resolves #33667

- [x] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added

packages/next/build/webpack-config.ts

@@ -48,6 +48,7 @@ import { regexLikeCss } from './webpack/config/blocks/css'
 import { CopyFilePlugin } from './webpack/plugins/copy-file-plugin'
 import { FlightManifestPlugin } from './webpack/plugins/flight-manifest-plugin'
 import { TelemetryPlugin } from './webpack/plugins/telemetry-plugin'
+import FunctionsManifestPlugin from './webpack/plugins/functions-manifest-plugin'
 import type { Span } from '../trace'
 import { getRawPageExtensions } from './utils'
 import browserslist from 'next/dist/compiled/browserslist'
@@ -1460,6 +1461,9 @@ export default async function getBaseWebpackConfig(
       // replacement is done before its process.env.* handling
       (!isServer || webServerRuntime) &&
         new MiddlewarePlugin({ dev, webServerRuntime }),
+      process.env.ENABLE_FILE_SYSTEM_API === '1' &&
+        webServerRuntime &&
+        new FunctionsManifestPlugin({ dev, webServerRuntime }),
       isServer && new NextJsSsrImportPlugin(),
       !isServer &&
         new BuildManifestPlugin({

packages/next/build/webpack/plugins/functions-manifest-plugin.ts

@@ -0,0 +1,68 @@
+import { sources, webpack5 } from 'next/dist/compiled/webpack/webpack'
+import { collectAssets, getEntrypointInfo } from './middleware-plugin'
+import { FUNCTIONS_MANIFEST } from '../../../shared/lib/constants'
+
+const PLUGIN_NAME = 'FunctionsManifestPlugin'
+export interface FunctionsManifest {
+  version: 1
+  pages: {
+    [page: string]: {
+      runtime: string
+      env: string[]
+      files: string[]
+      name: string
+      page: string
+      regexp: string
+    }
+  }
+}
+
+export default class FunctionsManifestPlugin {
+  dev: boolean
+  webServerRuntime: boolean
+
+  constructor({
+    dev,
+    webServerRuntime,
+  }: {
+    dev: boolean
+    webServerRuntime: boolean
+  }) {
+    this.dev = dev
+    this.webServerRuntime = webServerRuntime
+  }
+
+  createAssets(
+    compilation: webpack5.Compilation,
+    assets: any,
+    envPerRoute: Map<string, string[]>,
+    webServerRuntime: boolean
+  ) {
+    const functionsManifest: FunctionsManifest = {
+      version: 1,
+      pages: {},
+    }
+
+    const infos = getEntrypointInfo(compilation, envPerRoute, webServerRuntime)
+    infos.forEach((info) => {
+      functionsManifest.pages[info.page] = {
+        runtime: 'web',
+        ...info,
+      }
+    })
+
+    const assetPath =
+      (this.webServerRuntime ? '' : 'server/') + FUNCTIONS_MANIFEST
+    assets[assetPath] = new sources.RawSource(
+      JSON.stringify(functionsManifest, null, 2)
+    )
+  }
+
+  apply(compiler: webpack5.Compiler) {
+    collectAssets(compiler, this.createAssets.bind(this), {
+      dev: this.dev,
+      pluginName: PLUGIN_NAME,
+      webServerRuntime: this.webServerRuntime,
+    })
+  }
+}