CSF-Factories: Fix ConfigFile parser false warning on definePreview({...}).type<T>() export default

[Copilot]

• Understand the issue: ConfigFile parser warns on definePreview({...}).type<{...}>() in export default
• Fix ExportDefaultDeclaration handler in ConfigFile.ts to unwrap chained calls like .type<T>()
• Add test case for definePreview({...}).type<{...}>() in ConfigFile.test.ts
• Run tests to verify the fix (126 tests pass)
• Fix prettier formatting in ConfigFile.ts

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Bug]: ConfigFile parser warns on definePreview({...}).type<{...}>() in export default</issue_title>
<issue_description>### Describe the bug

When using .type() chaining on export default definePreview(...), the ConfigFile parser emits:

CSF Parsing error: Expected 'ObjectExpression' but found 'CallExpression' instead in 'CallExpression'.

This happens because the ExportDefaultDeclaration handler in ConfigFile.parse() only unwraps a single level of CallExpression:

// src/csf-tools/CsfFile.ts (ConfigFile class)
let decl = self._resolveDeclaration(node.declaration, parent);
t3.isCallExpression(decl) && t3.isObjectExpression(decl.arguments[0]) && (decl = decl.arguments[0]);
t3.isObjectExpression(decl) ? self._parseExportsObject(decl) : logger2.warn(...)

.type<T>() is a call with zero value arguments (only a TypeScript type parameter), so decl.arguments[0] is undefined, the unwrap fails, and the warning is emitted.

Note: The CallExpression visitor separately catches the nested definePreview({...}) call and parses it correctly, so the build still succeeds — but the warning is confusing and unnecessary.

Reproduction link

https://github.com/yuheiy/storybook-definepreview-type-csf-error

Reproduction steps

// .storybook/preview.tsx
import { definePreview } from '@storybook/react-vite';

export default definePreview({
  parameters: {
    /* ... */
  },
}).type<{
  parameters: {
    customParam?: string;
  };
}>();

storybook build
# or
storybook dev

System

│

│  Storybook Environment Info:
│

│  System:
│  OS: macOS 15.7.3
│  CPU: (10) arm64 Apple M1 Max
│  Shell: 5.9 - /bin/zsh
│  Binaries:
│  Node: 24.13.0 -
│  XXXXXXXX
│  Yarn: 2.4.3 -
│  /Users/yuhei.yasuda/.local/share/mise/installs/node/24.12.0/bin/yarn
│  npm: 11.6.2 -
│  /Users/yuhei.yasuda/.local/share/mise/installs/node/24.12.0/bin/npm
│  pnpm: 10.28.2 - /Users/yuhei.yasuda/Library/pnpm/pnpm <----- active
│  Browsers:
│  Chrome: 144.0.7559.133
│  Firefox: 146.0.1
│  Safari: 26.2
│  npmPackages:
│  @storybook/addon-a11y: ^10.2.4 => 10.2.4
│  @storybook/addon-docs: ^10.2.4 => 10.2.4
│  @storybook/addon-vitest: ^10.2.4 => 10.2.4
│  @storybook/react-vite: ^10.2.4 => 10.2.4
│  storybook: ^10.2.4 => 10.2.4

Additional context

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Bug]: ConfigFile parser warns on definePreview({...}).type<{...}>() in export default #33798

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Summary by CodeRabbit

• Bug Fixes

  • Improved parsing of complex factory declaration patterns to ensure more robust configuration file handling.

• Tests

  • Added test coverage for chained factory declaration patterns.

[github-actions]

	Fails
🚫	PR description is missing the mandatory "#### Manual testing" section. Please add it so that reviewers know how to manually test your changes.

Generated by 🚫 dangerJS against 2bdb54a

[nx-cloud]

View your CI Pipeline Execution ↗ for commit 2bdb54a

Command	Status	Duration	Result
nx run-many -t compile,check,knip,test,pretty-d...	❌ Failed	12m 16s	View ↗

---

☁️ Nx Cloud last updated this comment at 2026-03-03 10:09:39 UTC

[nx-cloud]

View your CI Pipeline Execution ↗ for commit f48a1ae

Command	Status	Duration	Result
nx run-many -t compile,check,knip,test,pretty-d...	❌ Failed	10m 18s	View ↗

---

☁️ Nx Cloud last updated this comment at 2026-02-20 12:01:20 UTC

[valentinpalkovic]

@copilot Fix linting issues as described in .github/copilot-instructions.md

[coderabbitai]

📝 Walkthrough

Walkthrough

Enhanced CSF factory declaration parsing by introducing iterative unwrapping logic to handle nested patterns like definePreview({...}).type<T>() in export default statements. Added corresponding test case validating the unwrapping behavior for chained method calls.

Changes

Cohort / File(s)	Summary
CSF Factory Unwrapping Logic code/core/src/csf-tools/ConfigFile.ts, code/core/src/csf-tools/ConfigFile.test.ts	Implemented iterative unwrapping loop in ExportDefaultDeclaration handling to recognize CSF factories wrapped in CallExpression and MemberExpression patterns. Added test case verifying correct parameter extraction from definePreview({...}).type<T>() chains.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• Core: Better handling for TypeScript satisfies/as syntaxes #32891: Adds unwrapping logic with _unwrap/_resolveDeclaration helpers for TypeScript type annotations and identifier resolution in export default handling.
• Addon-Vitest: Support vite/vitest config with deferred export #33755: Implements similar unwrapping mechanism for nested CallExpression and MemberExpression patterns in export-default expressions.

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• 📝 Generate docstrings (commit on current branch)

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@code/core/src/csf-tools/ConfigFile.test.ts`:
- Around line 296-312: The test must assert that no warning is emitted during
parse for the .type<T>() chaining case: wrap the call to
loadConfig(source).parse() with a spy on the warning emitter (e.g.,
jest.spyOn(console, 'warn') or the test logger used by loadConfig), call parse
via loadConfig(source).parse(), then expect the spy not to have been called, and
finally restore the spy; reference the existing loadConfig(...) and parse()
calls so you add the spy before parse and the expect(spy).not.toHaveBeenCalled()
after.

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ℹ️ Review info

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 558bede and 0e17410.

📒 Files selected for processing (2)

• code/core/src/csf-tools/ConfigFile.test.ts
• code/core/src/csf-tools/ConfigFile.ts

[coderabbitai]

⚠️ Potential issue | 🟠 Major

Assert warning suppression explicitly in this regression test.

This test only validates parsed data; it can still pass even if the parser logs the false warning again. Please also assert that no warning is emitted during parse for this .type<T>() pattern.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@code/core/src/csf-tools/ConfigFile.test.ts` around lines 296 - 312, The test
must assert that no warning is emitted during parse for the .type<T>() chaining
case: wrap the call to loadConfig(source).parse() with a spy on the warning
emitter (e.g., jest.spyOn(console, 'warn') or the test logger used by
loadConfig), call parse via loadConfig(source).parse(), then expect the spy not
to have been called, and finally restore the spy; reference the existing
loadConfig(...) and parse() calls so you add the spy before parse and the
expect(spy).not.toHaveBeenCalled() after.

[Copilot]

@copilot Fix linting issues as described in .github/copilot-instructions.md

Fixed in 2bdb54a — ran prettier on ConfigFile.ts which reformatted the multi-condition else if clause to split across multiple lines.