Mock: Catch errors when transforming preview files

[valentinpalkovic]

Closes #32192

What I did

I have added error handling when parsing and transforming preview files in the context of module mocking. When a preview file cannot be parsed, Storybook shouldn't crash, but rather log the error (debug loglevel)

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

Greptile Summary

This PR adds defensive error handling to Storybook's module mocking system when transforming preview files containing sb.mock() calls. The changes affect two key components: the Vite plugin and Webpack loader responsible for parsing and transforming these files.

The implementation wraps the rewriteSbMockImportCalls function in try-catch blocks in both transformation pipelines. When parsing or transformation fails, instead of crashing the build process, the system now logs a debug message and gracefully degrades - the Vite plugin returns null while the Webpack loader returns the original untransformed source code.

This change addresses issue #32192 where overly permissive regex patterns were causing build failures for files with 'preview' in their names (like 'my-orders-preview.ts') that aren't actually Storybook preview configuration files. The error handling follows an existing pattern in the codebase where extractMockCalls already has similar defensive error handling, making the mocking system more resilient to edge cases.

The changes integrate well with Storybook's existing error handling philosophy of graceful degradation rather than hard failures, ensuring that build processes continue even when individual files cannot be processed by the mocking transformation pipeline.

Confidence score: 4/5

• This PR is safe to merge with minimal risk as it adds defensive error handling without changing core functionality
• Score reflects well-implemented error handling that follows existing patterns, but lacks automated test coverage
• Pay close attention to the transformation logic to ensure the fallback behavior works correctly in production scenarios

[greptile-apps]

_{2 files reviewed, 2 comments}

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[nx-cloud]

View your CI Pipeline Execution ↗ for commit 1e2ff7b

Command	Status	Duration	Result
nx run-many -t build --parallel=3	✅ Succeeded	1m 9s	View ↗

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☁️ Nx Cloud last updated this comment at 2025-08-07 11:14:11 UTC

[storybook-app-bot]

Package Benchmarks

^{Commit: 1e2ff7b, ran on 7 August 2025 at 11:06:34 UTC}

The following packages have significant changes to their size or dependencies:

storybook

	Before	After	Difference
Dependency count	51	51	0
Self size	41.75 MB	41.74 MB	🎉 -15 KB 🎉
Dependency size	18.13 MB	18.13 MB	0 B
Bundle Size Analyzer	Link	Link

sb

	Before	After	Difference
Dependency count	52	52	0
Self size	1 KB	1 KB	0 B
Dependency size	59.89 MB	59.87 MB	🎉 -15 KB 🎉
Bundle Size Analyzer	Link	Link

@storybook/cli

	Before	After	Difference
Dependency count	220	220	0
Self size	585 KB	585 KB	0 B
Dependency size	104.38 MB	104.36 MB	🎉 -15 KB 🎉
Bundle Size Analyzer	Link	Link

@storybook/codemod

	Before	After	Difference
Dependency count	189	189	0
Self size	31 KB	31 KB	0 B
Dependency size	88.45 MB	88.44 MB	🎉 -15 KB 🎉
Bundle Size Analyzer	Link	Link