fix(#38743): config.runtime support template literal (#38750)

## Bug

- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

Fixes #38743.
Fixes: https://github.com/vercel/next.js/pull/38750

The PR adds basic `TemplateLiteral` support for static analysis.

The corresponding re-production of #38743 has also been implemented in e2e tests.

errors/invalid-page-config.md

@@ -1,39 +1,119 @@
-# Invalid Page Config
+# Invalid Page / API Route Config
 
 #### Why This Error Occurred
 
-In one of your pages you did `export const config` with an invalid value.
+In one of your pages or API Routes you did `export const config` with an invalid value.
 
 #### Possible Ways to Fix It
 
 The page's config must be an object initialized directly when being exported and not modified dynamically.
+The config object must only contains static constant literals without expressions.
 
-This is not allowed
+<table>
+<thead>
+  <tr>
+    <th>Not Allowed</th>
+    <th>Allowed</th>
+  </tr>
+</thead>
+<tbody>
+
+<tr>
+<td>
 
 ```js
+// `config` should be an object
 export const config = 'hello world'
 ```
 
-This is not allowed
+</td>
+<td>
 
 ```js
-const config = {}
-config.amp = true
+export const config = {}
 ```
 
-This is not allowed
+</td>
+</tr>
+
+<tr>
+<td>
 
 ```js
+export const config = {}
+// `config.amp` is defined after `config` is exported
+config.amp = true
+
+// `config.amp` contains a dynamic expression
+export const config = {
+  amp: 1 + 1 > 2,
+}
+```
+
+</td>
+<td>
+
+```js
+export const config = {
+  amp: true,
+}
+
+export const config = {
+  amp: false,
+}
+```
+
+</td>
+</tr>
+
+<tr>
+<td>
+
+```js
+// `config.runtime` contains a dynamic expression
+export const config = {
+  runtime: `node${'js'}`,
+}
+```
+
+</td>
+<td>
+
+```js
+export const config = {
+  runtime: 'nodejs',
+}
+export const config = {
+  runtime: `nodejs`,
+}
+```
+
+</td>
+</tr>
+
+<tr>
+<td>
+
+```js
+// Re-exported `config` is not allowed
 export { config } from '../config'
 ```
 
-This is allowed
+</td>
+<td>
 
 ```js
-export const config = { amp: true }
+export const config = {}
 ```
 
+</td>
+</tr>
+
+</tbody>
+</table>
+
 ### Useful Links
 
 - [Enabling AMP Support](https://nextjs.org/docs/advanced-features/amp-support/introduction)
 - [API Middlewares](https://nextjs.org/docs/api-routes/api-middlewares)
+- [Switchable Runtime](https://nextjs.org/docs/advanced-features/react-18/switchable-runtime)

packages/next/build/analysis/extract-const-value.ts

@@ -11,6 +11,7 @@ import type {
   ObjectExpression,
   RegExpLiteral,
   StringLiteral,
+  TemplateLiteral,
   VariableDeclaration,
 } from '@swc/core'
 
@@ -60,26 +61,6 @@ export function extractExportedConstValue(
   throw new NoSuchDeclarationError()
 }
 
-/**
- * A wrapper on top of `extractExportedConstValue` that returns undefined
- * instead of throwing when the thrown error is known.
- */
-export function tryToExtractExportedConstValue(
-  module: Module,
-  exportedName: string
-) {
-  try {
-    return extractExportedConstValue(module, exportedName)
-  } catch (error) {
-    if (
-      error instanceof UnsupportedValueError ||
-      error instanceof NoSuchDeclarationError
-    ) {
-      return undefined
-    }
-  }
-}
-
 function isExportDeclaration(node: Node): node is ExportDeclaration {
   return node.type === 'ExportDeclaration'
 }
@@ -124,8 +105,12 @@ function isRegExpLiteral(node: Node): node is RegExpLiteral {
   return node.type === 'RegExpLiteral'
 }
 
-class UnsupportedValueError extends Error {}
-class NoSuchDeclarationError extends Error {}
+function isTemplateLiteral(node: Node): node is TemplateLiteral {
+  return node.type === 'TemplateLiteral'
+}
+
+export class UnsupportedValueError extends Error {}
+export class NoSuchDeclarationError extends Error {}
 
 function extractValue(node: Node): any {
   if (isNullLiteral(node)) {
@@ -191,6 +176,25 @@ function extractValue(node: Node): any {
     }
 
     return obj
+  } else if (isTemplateLiteral(node)) {
+    // e.g. `abc`
+    if (node.expressions.length !== 0) {
+      // TODO: should we add support for `${'e'}d${'g'}'e'`?
+      throw new UnsupportedValueError()
+    }
+
+    // When TemplateLiteral has 0 expressions, the length of quasis is always 1.
+    // Because when parsing TemplateLiteral, the parser yields the first quasi,
+    // then the first expression, then the next quasi, then the next expression, etc.,
+    // until the last quasi.
+    // Thus if there is no expression, the parser ends at the frst and also last quasis
+    //
+    // A "cooked" interpretation where backslashes have special meaning, while a
+    // "raw" interpretation where backslashes do not have special meaning
+    // https://exploringjs.com/impatient-js/ch_template-literals.html#template-strings-cooked-vs-raw
+    const [{ cooked, raw }] = node.quasis
+
+    return cooked ?? raw
   } else {
     throw new UnsupportedValueError()
   }

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

@@ -1,6 +1,9 @@
 import { isServerRuntime, ServerRuntime } from '../../server/config-shared'
 import type { NextConfig } from '../../server/config-shared'
-import { tryToExtractExportedConstValue } from './extract-const-value'
+import {
+  extractExportedConstValue,
+  UnsupportedValueError,
+} from './extract-const-value'
 import { escapeStringRegexp } from '../../shared/lib/escape-regexp'
 import { parseModule } from './parse-module'
 import { promises as fs } from 'fs'
@@ -32,13 +35,23 @@ export async function getPageStaticInfo(params: {
   isDev?: boolean
   page?: string
 }): Promise<PageStaticInfo> {
-  const { isDev, pageFilePath, nextConfig } = params
+  const { isDev, pageFilePath, nextConfig, page } = params
 
   const fileContent = (await tryToReadFile(pageFilePath, !isDev)) || ''
   if (/runtime|getStaticProps|getServerSideProps|matcher/.test(fileContent)) {
     const swcAST = await parseModule(pageFilePath, fileContent)
     const { ssg, ssr } = checkExports(swcAST)
-    const config = tryToExtractExportedConstValue(swcAST, 'config') || {}
+
+    // default / failsafe value for config
+    let config: any = {}
+    try {
+      config = extractExportedConstValue(swcAST, 'config')
+    } catch (e) {
+      if (e instanceof UnsupportedValueError) {
+        warnAboutUnsupportedValue(pageFilePath, page)
+      }
+      // `export config` doesn't exist, or other unknown error throw by swc, silence them
+    }
 
     if (
       typeof config.runtime !== 'string' &&
@@ -218,3 +231,19 @@ function warnAboutExperimentalEdgeApiFunctions() {
 }
 
 let warnedAboutExperimentalEdgeApiFunctions = false
+
+const warnedUnsupportedValueMap = new Map<string, boolean>()
+function warnAboutUnsupportedValue(
+  pageFilePath: string,
+  page: string | undefined
+) {
+  if (warnedUnsupportedValueMap.has(pageFilePath)) {
+    return
+  }
+  Log.warn(
+    `You have exported a \`config\` field in ${
+      page ? `route "${page}"` : `"${pageFilePath}"`
+    } that Next.js can't recognize, so it will be ignored. See: https://nextjs.org/docs/messages/invalid-page-config`
+  )
+  warnedUnsupportedValueMap.set(pageFilePath, true)
+}

test/e2e/switchable-runtime/index.test.ts

@@ -115,11 +115,15 @@ describe('Switchable runtime', () => {
         )
       })
 
-      it('should build /api/hello as an api route with edge runtime', async () => {
-        const response = await fetchViaHTTP(context.appPort, '/api/hello')
-        const text = await response.text()
+      it('should build /api/hello and /api/edge as an api route with edge runtime', async () => {
+        let response = await fetchViaHTTP(context.appPort, '/api/hello')
+        let text = await response.text()
         expect(text).toMatch(/Hello from .+\/api\/hello/)
 
+        response = await fetchViaHTTP(context.appPort, '/api/edge')
+        text = await response.text()
+        expect(text).toMatch(/Returned by Edge API Route .+\/api\/edge/)
+
         if (!(global as any).isNextDeploy) {
           const manifest = await readJson(
             join(context.appDir, '.next/server/middleware-manifest.json')
@@ -137,6 +141,17 @@ describe('Switchable runtime', () => {
                 regexp: '^/api/hello$',
                 wasm: [],
               },
+              '/api/edge': {
+                env: [],
+                files: [
+                  'server/edge-runtime-webpack.js',
+                  'server/pages/api/edge.js',
+                ],
+                name: 'pages/api/edge',
+                page: '/api/edge',
+                regexp: '^/api/edge$',
+                wasm: [],
+              },
             },
           })
         }
@@ -235,11 +250,15 @@ describe('Switchable runtime', () => {
         })
       })
 
-      it('should build /api/hello as an api route with edge runtime', async () => {
-        const response = await fetchViaHTTP(context.appPort, '/api/hello')
-        const text = await response.text()
+      it('should build /api/hello and /api/edge as an api route with edge runtime', async () => {
+        let response = await fetchViaHTTP(context.appPort, '/api/hello')
+        let text = await response.text()
         expect(text).toMatch(/Hello from .+\/api\/hello/)
 
+        response = await fetchViaHTTP(context.appPort, '/api/edge')
+        text = await response.text()
+        expect(text).toMatch(/Returned by Edge API Route .+\/api\/edge/)
+
         if (!(global as any).isNextDeploy) {
           const manifest = await readJson(
             join(context.appDir, '.next/server/middleware-manifest.json')
@@ -257,6 +276,17 @@ describe('Switchable runtime', () => {
                 regexp: '^/api/hello$',
                 wasm: [],
               },
+              '/api/edge': {
+                env: [],
+                files: [
+                  'server/edge-runtime-webpack.js',
+                  'server/pages/api/edge.js',
+                ],
+                name: 'pages/api/edge',
+                page: '/api/edge',
+                regexp: '^/api/edge$',
+                wasm: [],
+              },
             },
           })
         }

test/e2e/switchable-runtime/pages/api/edge.js

@@ -0,0 +1,7 @@
+export default (req) => {
+  return new Response(`Returned by Edge API Route ${req.url}`)
+}
+
+export const config = {
+  runtime: `experimental-edge`,
+}

test/production/exported-runtimes-value-validation/index.test.ts

@@ -4,7 +4,7 @@ import path from 'path'
 describe('Exported runtimes value validation', () => {
   test('fails to build on malformed input', async () => {
     const result = await nextBuild(
-      path.resolve(__dirname, './app'),
+      path.resolve(__dirname, './invalid-runtime/app'),
       undefined,
       { stdout: true, stderr: true }
     )
@@ -15,4 +15,19 @@ describe('Exported runtimes value validation', () => {
       ),
     })
   })
+
+  test('warns on unrecognized runtimes value', async () => {
+    const result = await nextBuild(
+      path.resolve(__dirname, './unsupported-syntax/app'),
+      undefined,
+      { stdout: true, stderr: true }
+    )
+
+    expect(result).toMatchObject({
+      code: 0,
+      stderr: expect.stringContaining(
+        `You have exported a \`config\` field in route "/" that Next.js can't recognize, so it will be ignored`
+      ),
+    })
+  })
 })

test/production/exported-runtimes-value-validation/unsupported-syntax/app/pages/index.js

@@ -0,0 +1,7 @@
+export default function Page() {
+  return <p>hello world</p>
+}
+
+export const config = {
+  runtime: `something-${'real' + 1 + 'y odd'}`,
+}