From a76c67df1e5320709dde14a17a97c64f3a397380 Mon Sep 17 00:00:00 2001
From: Michael Shilman <shilman@users.noreply.github.com>
Date: Fri, 21 Apr 2023 10:32:05 +0800
Subject: [PATCH] CSF: Improve error message for bad default export

---
 code/lib/csf-tools/src/CsfFile.test.ts | 13 +++++++++++++
 code/lib/csf-tools/src/CsfFile.ts      | 14 +++++++++++---
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/code/lib/csf-tools/src/CsfFile.test.ts b/code/lib/csf-tools/src/CsfFile.test.ts
index e54a063c0249..6250ea1c3696 100644
--- a/code/lib/csf-tools/src/CsfFile.test.ts
+++ b/code/lib/csf-tools/src/CsfFile.test.ts
@@ -548,6 +548,19 @@ describe('CsfFile', () => {
       ).toThrow('CSF: missing default export');
     });
 
+    it('bad meta', () => {
+      expect(() =>
+        parse(
+          dedent`
+          const foo = bar();
+          export default foo;
+          export const A = () => {};
+          export const B = () => {};
+      `
+        )
+      ).toThrow('CSF: default export must be an object');
+    });
+
     it('no metadata', () => {
       expect(() =>
         parse(
diff --git a/code/lib/csf-tools/src/CsfFile.ts b/code/lib/csf-tools/src/CsfFile.ts
index b7b3a07412f3..bfc9716e425b 100644
--- a/code/lib/csf-tools/src/CsfFile.ts
+++ b/code/lib/csf-tools/src/CsfFile.ts
@@ -105,9 +105,9 @@ export interface CsfOptions {
 }
 
 export class NoMetaError extends Error {
-  constructor(ast: t.Node, fileName?: string) {
+  constructor(message: string, ast: t.Node, fileName?: string) {
     super(dedent`
-      CSF: missing default export ${formatLocation(ast, fileName)}
+      CSF: ${message} ${formatLocation(ast, fileName)}
 
       More info: https://storybook.js.org/docs/react/writing-stories/introduction#default-export
     `);
@@ -272,6 +272,14 @@ export class CsfFile {
             self._metaNode = metaNode;
             self._parseMeta(metaNode, parent);
           }
+
+          if (self._metaStatement && !self._metaNode) {
+            throw new NoMetaError(
+              'default export must be an object',
+              self._metaStatement,
+              self._fileName
+            );
+          }
         },
       },
       ExportNamedDeclaration: {
@@ -435,7 +443,7 @@ export class CsfFile {
     });
 
     if (!self._meta) {
-      throw new NoMetaError(self._ast, self._fileName);
+      throw new NoMetaError('missing default export', self._ast, self._fileName);
     }
 
     if (!self._meta.title && !self._meta.component) {