Addon Vitest: Fix support for plain stories.tsx files

[ghengeveld]

Closes #31966

What I did

Removed a check against a file pattern in the vitest transformer which was preventing stories.tsx files from being transformed, thereby crashing Vitest. We already check against stories globs higher up the chain so we don't need the check in the transformer.

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.

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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 removes an overly restrictive file pattern check in the Vitest transformer that was preventing files named stories.tsx (without a component prefix) from being properly processed. The change simplifies the code by removing redundant validation that was already being handled by Storybook's glob patterns higher up in the build chain.

This fix addresses issue #31966 where files named stories.tsx were being skipped by the transformer, causing Vitest to crash. The removed check was superfluous since Storybook already handles story file detection through its glob patterns at a higher level.

The changes involve:

1. Removing the .stor(y|ies)\. regex check from the transformer
2. Removing associated test cases that were validating this now-removed functionality

Confidence score: 5/5

1. This PR is extremely safe to merge as it removes redundant validation
2. The score is 5/5 because the change is a straightforward removal of duplicate validation that was causing issues, with the proper validation already being handled elsewhere in the codebase
3. Files that need attention:
   • code/core/src/csf-tools/vitest-plugin/transformer.ts
   • code/core/src/csf-tools/vitest-plugin/transformer.test.ts

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☁️ Nx Cloud last updated this comment at 2025-07-15 08:28:51 UTC

[storybook-app-bot]

Package Benchmarks

^{Commit: 86cf4e4, ran on 15 July 2025 at 08:16:10 UTC}

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

storybook

	Before	After	Difference
Dependency count	51	51	0
Self size	31.75 MB	31.76 MB	🚨 +15 KB 🚨
Dependency size	17.43 MB	17.43 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	49.18 MB	49.20 MB	🚨 +15 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/cli

	Before	After	Difference
Dependency count	217	217	0
Self size	582 KB	582 KB	0 B
Dependency size	93.66 MB	93.68 MB	🚨 +18 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/codemod

	Before	After	Difference
Dependency count	186	186	0
Self size	31 KB	31 KB	0 B
Dependency size	77.76 MB	77.77 MB	🚨 +12 KB 🚨
Bundle Size Analyzer	Link	Link