Core: Ignore empty files when indexing

code/.eslintignore

@@ -19,4 +19,5 @@ ember-output
 !.storybook
 core/assets
 core/src/core-server/utils/__search-files-tests__
+core/src/core-server/utils/__mockdata__/src/Empty.stories.ts
 core/report

code/core/src/core-server/presets/common-preset.ts

@@ -13,7 +13,7 @@ import {
   removeAddon as removeAddonBase,
 } from 'storybook/internal/common';
 import { StoryIndexGenerator } from 'storybook/internal/core-server';
-import { readCsf } from 'storybook/internal/csf-tools';
+import { loadCsf } from 'storybook/internal/csf-tools';
 import { logger } from 'storybook/internal/node-logger';
 import { telemetry } from 'storybook/internal/telemetry';
 import type {
@@ -215,7 +215,14 @@ export const features: PresetProperty<'features'> = async (existing) => ({
 
 export const csfIndexer: Indexer = {
   test: /(stories|story)\.(m?js|ts)x?$/,
-  createIndex: async (fileName, options) => (await readCsf(fileName, options)).parse().indexInputs,
+  createIndex: async (fileName, options) => {
+    const code = (await readFile(fileName, 'utf-8')).toString();
+    if (code.trim().length === 0) {
+      logger.debug(`The file ${fileName} is empty. Skipping indexing.`);
+      return [];
+    }
+    return loadCsf(code, { ...options, fileName }).parse().indexInputs;
+  },
 };
 
 export const experimental_indexers: PresetProperty<'experimental_indexers'> = (existingIndexers) =>

code/core/src/core-server/utils/StoryIndexGenerator.test.ts

@@ -4,7 +4,7 @@ import { beforeEach, describe, expect, it, vi } from 'vitest';
 
 import { normalizeStoriesEntry } from 'storybook/internal/common';
 import { toId } from 'storybook/internal/csf';
-import { getStorySortParameter, readCsf } from 'storybook/internal/csf-tools';
+import { getStorySortParameter, loadCsf } from 'storybook/internal/csf-tools';
 import { logger, once } from 'storybook/internal/node-logger';
 import type { NormalizedStoriesSpecifier, StoryIndexEntry } from 'storybook/internal/types';
 
@@ -34,13 +34,13 @@ vi.mock('storybook/internal/csf-tools', async (importOriginal) => {
   const csfTools = await importOriginal<typeof import('storybook/internal/csf-tools')>();
   return {
     ...csfTools,
-    readCsf: vi.fn(csfTools.readCsf),
+    loadCsf: vi.fn(csfTools.loadCsf),
     getStorySortParameter: vi.fn(csfTools.getStorySortParameter),
   };
 });
 
 const toIdMock = vi.mocked(toId);
-const readCsfMock = vi.mocked(readCsf);
+const loadCsfMock = vi.mocked(loadCsf);
 const getStorySortParameterMock = vi.mocked(getStorySortParameter);
 
 const options: StoryIndexGeneratorOptions = {
@@ -55,7 +55,7 @@ describe('StoryIndexGenerator', () => {
     vi.mocked(logger.warn).mockClear();
     vi.mocked(once.warn).mockClear();
     toIdMock.mockClear();
-    readCsfMock.mockClear();
+    loadCsfMock.mockClear();
     getStorySortParameterMock.mockClear();
     StoryIndexGenerator.clearFindMatchingFilesCache();
   });
@@ -221,6 +221,25 @@ describe('StoryIndexGenerator', () => {
         `);
       });
     });
+    describe('empty or whitespace-only files', () => {
+      it('ignores story files that only contain whitespace (e.g. just a newline)', async () => {
+        const specifier: NormalizedStoriesSpecifier = normalizeStoriesEntry(
+          './src/Empty.stories.ts',
+          options
+        );
+
+        const generator = new StoryIndexGenerator([specifier], options);
+        await generator.initialize();
+
+        const { storyIndex } = await generator.getIndexAndStats();
+        expect(storyIndex).toMatchInlineSnapshot(`
+          {
+            "entries": {},
+            "v": 5,
+          }
+        `);
+      });
+    });
     describe('non-recursive specifier', () => {
       it('extracts stories from the right files', async () => {
         const specifier: NormalizedStoriesSpecifier = normalizeStoriesEntry(
@@ -2135,16 +2154,16 @@ describe('StoryIndexGenerator', () => {
           options
         );
 
-        readCsfMock.mockClear();
-        expect(readCsfMock).toHaveBeenCalledTimes(0);
+        loadCsfMock.mockClear();
+        expect(loadCsfMock).toHaveBeenCalledTimes(0);
         const generator = new StoryIndexGenerator([specifier], options);
         await generator.initialize();
         await generator.getIndex();
-        expect(readCsfMock).toHaveBeenCalledTimes(12);
+        expect(loadCsfMock).toHaveBeenCalledTimes(12);
 
-        readCsfMock.mockClear();
+        loadCsfMock.mockClear();
         await generator.getIndex();
-        expect(readCsfMock).not.toHaveBeenCalled();
+        expect(loadCsfMock).not.toHaveBeenCalled();
       });
 
       it('does not extract docs files a second time', async () => {
@@ -2156,8 +2175,8 @@ describe('StoryIndexGenerator', () => {
           './src/docs2/*.mdx',
           options
         );
-        readCsfMock.mockClear();
-        expect(readCsfMock).toHaveBeenCalledTimes(0);
+        loadCsfMock.mockClear();
+        expect(loadCsfMock).toHaveBeenCalledTimes(0);
         const generator = new StoryIndexGenerator([storiesSpecifier, docsSpecifier], options);
         await generator.initialize();
         await generator.getIndex();
@@ -2194,17 +2213,17 @@ describe('StoryIndexGenerator', () => {
           options
         );
 
-        readCsfMock.mockClear();
+        loadCsfMock.mockClear();
         const generator = new StoryIndexGenerator([specifier], options);
         await generator.initialize();
         await generator.getIndex();
-        expect(readCsfMock).toHaveBeenCalledTimes(12);
+        expect(loadCsfMock).toHaveBeenCalledTimes(12);
 
         generator.invalidate('./src/B.stories.ts', false);
 
-        readCsfMock.mockClear();
+        loadCsfMock.mockClear();
         await generator.getIndex();
-        expect(readCsfMock).toHaveBeenCalledTimes(1);
+        expect(loadCsfMock).toHaveBeenCalledTimes(1);
       });
 
       it('calls extract docs file for just the one file', async () => {
@@ -2279,17 +2298,17 @@ describe('StoryIndexGenerator', () => {
           options
         );
 
-        readCsfMock.mockClear();
+        loadCsfMock.mockClear();
         const generator = new StoryIndexGenerator([specifier], options);
         await generator.initialize();
         await generator.getIndex();
-        expect(readCsfMock).toHaveBeenCalledTimes(12);
+        expect(loadCsfMock).toHaveBeenCalledTimes(12);
 
         generator.invalidate('./src/B.stories.ts', true);
 
-        readCsfMock.mockClear();
+        loadCsfMock.mockClear();
         await generator.getIndex();
-        expect(readCsfMock).not.toHaveBeenCalled();
+        expect(loadCsfMock).not.toHaveBeenCalled();
       });
 
       it('does call the sort function a second time', async () => {
@@ -2318,11 +2337,11 @@ describe('StoryIndexGenerator', () => {
           options
         );
 
-        readCsfMock.mockClear();
+        loadCsfMock.mockClear();
         const generator = new StoryIndexGenerator([specifier], options);
         await generator.initialize();
         await generator.getIndex();
-        expect(readCsfMock).toHaveBeenCalledTimes(12);
+        expect(loadCsfMock).toHaveBeenCalledTimes(12);
 
         generator.invalidate('./src/B.stories.ts', true);