From ed4eae8e9554c1d8646496d2a0b4fb55c6fd264e Mon Sep 17 00:00:00 2001
From: SukkaW <isukkaw@gmail.com>
Date: Mon, 18 Jul 2022 23:18:05 +0800
Subject: [PATCH] feat: show a warning about unrecognized `export config`

---
 .../build/analysis/extract-const-value.ts     |  4 +--
 .../build/analysis/get-page-static-info.ts    | 29 +++++++++++++++++--
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/packages/next/build/analysis/extract-const-value.ts b/packages/next/build/analysis/extract-const-value.ts
index edfb89ea5e29..0cca5dfaba89 100644
--- a/packages/next/build/analysis/extract-const-value.ts
+++ b/packages/next/build/analysis/extract-const-value.ts
@@ -129,8 +129,8 @@ function isTemplateLiteral(node: Node): node is TemplateLiteral {
   return node.type === 'TemplateLiteral'
 }
 
-class UnsupportedValueError extends Error {}
-class NoSuchDeclarationError extends Error {}
+export class UnsupportedValueError extends Error {}
+export class NoSuchDeclarationError extends Error {}
 
 function extractValue(node: Node): any {
   if (isNullLiteral(node)) {
diff --git a/packages/next/build/analysis/get-page-static-info.ts b/packages/next/build/analysis/get-page-static-info.ts
index 60d94aa800e3..1a65f630c02b 100644
--- a/packages/next/build/analysis/get-page-static-info.ts
+++ b/packages/next/build/analysis/get-page-static-info.ts
@@ -1,6 +1,10 @@
 import { isServerRuntime, ServerRuntime } from '../../server/config-shared'
 import type { NextConfig } from '../../server/config-shared'
-import { tryToExtractExportedConstValue } from './extract-const-value'
+import {
+  extractExportedConstValue,
+  NoSuchDeclarationError,
+  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 +36,32 @@ 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 value for config
+    let config: any = {}
+    try {
+      config = extractExportedConstValue(swcAST, 'config')
+    } catch (e) {
+      if (e instanceof UnsupportedValueError) {
+        // `export config` is found, but can't extract the value of it
+        Log.warn(
+          `You have exported a \`config\` field in "${
+            page || pageFilePath
+          }" that Next.js can't recognize, so it will be ignored`
+        )
+      } else if (e instanceof NoSuchDeclarationError) {
+        // Can not find `export config` in the file, just ignore it
+      } else {
+        // Unknown error, throw it
+        throw e
+      }
+    }
 
     if (
       typeof config.runtime !== 'string' &&