Fix invalid config export errors

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
                   }
 

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>

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>

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>