From 0992642c08b1f6022b0ddbfd219d2a13d391f047 Mon Sep 17 00:00:00 2001
From: JJ Kasper <jj@jjsweb.site>
Date: Fri, 4 Sep 2020 08:19:12 -0500
Subject: [PATCH] Fix invalid config export errors (#16834)

This corrects detecting of invalid page config exports and adds additional test cases for non-invalid config import/exports

Closes: https://github.com/vercel/next.js/issues/16775
---
 .../build/babel/plugins/next-page-config.ts   | 41 +++++++++++++++----
 .../page-config/pages/valid/config-import.js  | 10 +++++
 .../pages/valid/not-config-export.js          | 10 +++++
 .../pages/valid/not-config-import-export.js   | 12 ++++++
 4 files changed, 66 insertions(+), 7 deletions(-)
 create mode 100644 test/integration/page-config/pages/valid/config-import.js
 create mode 100644 test/integration/page-config/pages/valid/not-config-export.js
 create mode 100644 test/integration/page-config/pages/valid/not-config-import-export.js

diff --git a/packages/next/build/babel/plugins/next-page-config.ts b/packages/next/build/babel/plugins/next-page-config.ts
index 1e836f23dddb37..8f6955a4201b50 100644
--- a/packages/next/build/babel/plugins/next-page-config.ts
+++ b/packages/next/build/babel/plugins/next-page-config.ts
@@ -82,20 +82,47 @@ export default function nextPageConfig({
                   exportPath.scope.getBinding(CONFIG_KEY)?.path.node,
                 ].filter(Boolean)
 
-                for (const declaration of declarations) {
-                  if (
-                    !BabelTypes.isIdentifier(declaration.id, {
-                      name: CONFIG_KEY,
-                    })
-                  ) {
-                    if (BabelTypes.isImportSpecifier(declaration)) {
+                for (const specifier of exportPath.node.specifiers) {
+                  if (specifier.exported.name === CONFIG_KEY) {
+                    // export {} from 'somewhere'
+                    if (BabelTypes.isStringLiteral(exportPath.node.source)) {
                       throw new Error(
                         errorMessage(
                           exportState,
                           `Expected object but got import`
                         )
                       )
+                      // import hello from 'world'
+                      // export { hello as config }
+                    } else if (
+                      BabelTypes.isIdentifier(
+                        (specifier as BabelTypes.ExportSpecifier).local
+                      )
+                    ) {
+                      if (
+                        BabelTypes.isImportSpecifier(
+                          exportPath.scope.getBinding(
+                            (specifier as BabelTypes.ExportSpecifier).local.name
+                          )?.path.node
+                        )
+                      ) {
+                        throw new Error(
+                          errorMessage(
+                            exportState,
+                            `Expected object but got import`
+                          )
+                        )
+                      }
                     }
+                  }
+                }
+
+                for (const declaration of declarations) {
+                  if (
+                    !BabelTypes.isIdentifier(declaration.id, {
+                      name: CONFIG_KEY,
+                    })
+                  ) {
                     continue
                   }
 
diff --git a/test/integration/page-config/pages/valid/config-import.js b/test/integration/page-config/pages/valid/config-import.js
new file mode 100644
index 00000000000000..c02078ca909c38
--- /dev/null
+++ b/test/integration/page-config/pages/valid/config-import.js
@@ -0,0 +1,10 @@
+// eslint-disable-next-line no-unused-vars
+import { config } from '../../config'
+
+export const getServerSideProps = () => {
+  return {
+    props: {},
+  }
+}
+
+export default () => <p>hello world</p>
diff --git a/test/integration/page-config/pages/valid/not-config-export.js b/test/integration/page-config/pages/valid/not-config-export.js
new file mode 100644
index 00000000000000..90763cd90d9204
--- /dev/null
+++ b/test/integration/page-config/pages/valid/not-config-export.js
@@ -0,0 +1,10 @@
+// eslint-disable-next-line no-unused-vars
+export { config as notConfig } from '../../config'
+
+export const getServerSideProps = () => {
+  return {
+    props: {},
+  }
+}
+
+export default () => <p>hello world</p>
diff --git a/test/integration/page-config/pages/valid/not-config-import-export.js b/test/integration/page-config/pages/valid/not-config-import-export.js
new file mode 100644
index 00000000000000..6f5c3c13f3bf8a
--- /dev/null
+++ b/test/integration/page-config/pages/valid/not-config-import-export.js
@@ -0,0 +1,12 @@
+// eslint-disable-next-line no-unused-vars
+import { config } from '../../config'
+
+export { config as notConfig }
+
+export const getServerSideProps = () => {
+  return {
+    props: {},
+  }
+}
+
+export default () => <p>hello world</p>