[build] validate the exported config values (#38370)

Right now if people will accidentally export a typo like `runtime: 'experimental-egde'` we will fail silently.
This commit ensures we will throw and fail loudly when such typos occur.

## Bug

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

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

@@ -1,4 +1,4 @@
-import type { ServerRuntime } from '../../server/config-shared'
+import { isServerRuntime, ServerRuntime } from '../../server/config-shared'
 import type { NextConfig } from '../../server/config-shared'
 import { tryToExtractExportedConstValue } from './extract-const-value'
 import { escapeStringRegexp } from '../../shared/lib/escape-regexp'
@@ -40,6 +40,24 @@ export async function getPageStaticInfo(params: {
     const { ssg, ssr } = checkExports(swcAST)
     const config = tryToExtractExportedConstValue(swcAST, 'config') || {}
 
+    if (
+      typeof config.runtime !== 'string' &&
+      typeof config.runtime !== 'undefined'
+    ) {
+      throw new Error(`Provided runtime `)
+    } else if (!isServerRuntime(config.runtime)) {
+      const options = Object.values(SERVER_RUNTIME).join(', ')
+      if (typeof config.runtime !== 'string') {
+        throw new Error(
+          `The \`runtime\` config must be a string. Please leave it empty or choose one of: ${options}`
+        )
+      } else {
+        throw new Error(
+          `Provided runtime "${config.runtime}" is not supported. Please leave it empty or choose one of: ${options}`
+        )
+      }
+    }
+
     let runtime =
       SERVER_RUNTIME.edge === config?.runtime
         ? SERVER_RUNTIME.edge

packages/next/server/config-shared.ts

@@ -561,3 +561,9 @@ export async function normalizeConfig(phase: string, config: any) {
   // Support `new Promise` and `async () =>` as return values of the config export
   return await config
 }
+
+export function isServerRuntime(value?: string): value is ServerRuntime {
+  return (
+    value === undefined || value === 'nodejs' || value === 'experimental-edge'
+  )
+}

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

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

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

@@ -0,0 +1,18 @@
+import { nextBuild } from 'next-test-utils'
+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'),
+      undefined,
+      { stdout: true, stderr: true }
+    )
+    expect(result).toMatchObject({
+      code: 1,
+      stderr: expect.stringContaining(
+        `Provided runtime "something-odd" is not supported.`
+      ),
+    })
+  })
+})