CLI: Skip a11y addon automigration prompting when not applicable

[yannbf]

Closes #

What I did

The addon-a11y-addon-test automigration was prompted for projects where it had nothing to do. Its check() only evaluated the "already migrated" skip conditions when both .storybook/vitest.setup.* and .storybook/preview.* existed:

if (vitestSetupFile && previewFile) {
  ...
  if (skipVitestSetupTransformation && skipPreviewTransformation) {
    return null; // the only "don't prompt" exit
  }
}

Projects without a vitest.setup file — the norm since the vitest plugin auto-provisions preview annotations (10.3+) — skipped that block entirely, so the migration was always prompted even when preview already had parameters.a11y.test configured. Selecting it was a complete no-op (it rewrote preview with identical content).

This PR computes the two skip flags independently per file:

• No vitest.setup file → nothing to transform on the setup side (the plugin auto-provisions annotations, including addon-a11y's). Projects that keep the optional setup file are still checked and transformed exactly as before.
• The preview file is checked on its own, regardless of whether a setup file exists.
• The early return null now runs whenever both flags are set.

This also fixes a second latent bug the old gating had: a project with an already-migrated setup file but no preview file skipped the "already has @storybook/addon-a11y" detection and re-transformed the setup file, injecting a duplicate a11yAddonAnnotations import.

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

Includes a regression test for the false-positive scenario (no setup file + preview already configured → check() returns null), and un-skips the previously skipped "preview file only" test with a corrected expectation.

Manual testing

1. Take a project with @storybook/addon-a11y and @storybook/addon-vitest in main.ts, no .storybook/vitest.setup.* file, and parameters: { a11y: { test: 'todo' } } already set in .storybook/preview.* (e.g. https://github.com/yannbf/mealdrop).
2. Run npx storybook@next upgrade (or yarn automigrate from a linked CLI build).
3. Before this fix: the addon-a11y-addon-test automigration is prompted and does nothing when run. After: it is not prompted.
4. Also verify a legacy project with a .storybook/vitest.setup.ts lacking the a11y annotations still gets prompted and transformed as before.

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
• Declare whether manual QA will be needed for this PR during the next release, through qa:needed or qa:skip

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved automigration checks for Storybook preview and Vitest setup files so updates are only suggested when needed.
  • Better handles cases where the preview file already includes the required changes, avoiding unnecessary transformations.
  • More accurately skips setup changes when transformation isn’t possible or no longer required.

[coderabbitai]

📝 Walkthrough

Walkthrough

The automigration for the a11y addon test now computes skipVitestSetupTransformation and skipPreviewTransformation independently rather than requiring both files to exist together, with earlier null returns when both are skipped. Catch clauses in two helper functions were simplified. Corresponding tests were enabled, updated, and extended.

Changes

Independent Skip-Flag Migration Logic

Layer / File(s)	Summary
Independent transformation flags code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.ts	Replaces combined vitest setup/preview existence check with independently initialized and computed skipVitestSetupTransformation/skipPreviewTransformation flags, returns null earlier when both are skipped, and simplifies catch (e) to catch in two helper functions.
Updated test expectations and coverage code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.test.ts	Enables a previously skipped test, updates expected skipVitestSetupTransformation values across scenarios, and adds a case asserting check returns null when vitest.setup is missing but preview already contains required transformations.

Estimated code review effort: 2 (Simple) | ~10 minutes

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

---

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[coderabbitai]

Actionable comments posted: 2

🧹 Nitpick comments (1)

code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.ts (1)

80-96: 🚀 Performance & Scalability | 🔵 Trivial | 💤 Low value

Files are read twice (once here, once in getTransformedSetupCode/getTransformedPreviewCode).

vitestSetupFile/previewFile are each read via readFileSync here to compute skip flags, then read again inside getTransformedSetupCode/getTransformedPreviewCode (Lines 108, 121) if not skipped. Since this pattern predates this diff, it's not a regression, but caching the source read once would avoid redundant I/O and reduce inconsistency risk (e.g., file changing between reads).

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.ts` around
lines 80 - 96, The `add`/skip-flag logic in `addon-a11y-addon-test.ts` reads
`vitestSetupFile` and `previewFile` twice, once in this precheck block and again
in `getTransformedSetupCode`/`getTransformedPreviewCode`. Refactor the flow so
the file contents are read once, cached, and reused to compute
`skipVitestSetupTransformation`/`skipPreviewTransformation` and to feed the
transformation helpers, avoiding duplicate `readFileSync` calls and inconsistent
reads.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.test.ts`:
- Around line 198-232: The current coverage only exercises the case where
vitest.setup is missing and the preview file is already transformed, but it
misses the mirrored path where previewFile is absent and vitest.setup is already
migrated. Add a symmetric test in addonA11yAddonTest.check that mocks the
preview file as missing while providing a migrated vitest.setup, and assert it
returns null; this will cover the skipPreviewTransformation default behavior in
the same check flow.

In `@code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.ts`:
- Around line 77-100: The default handling for preview transformation is
incomplete in check(), causing a migration result even when previewFile is
absent. Update add-on-a11y addon test logic so skipPreviewTransformation is
initialized from !previewFile, and keep the existing preview-file
read/shouldPreviewFileBeTransformed flow only when previewFile exists. Verify
the early return in check() now skips the auto flow when both transformations
are unavailable, and add a test covering the missing-preview case.

---

Nitpick comments:
In `@code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.ts`:
- Around line 80-96: The `add`/skip-flag logic in `addon-a11y-addon-test.ts`
reads `vitestSetupFile` and `previewFile` twice, once in this precheck block and
again in `getTransformedSetupCode`/`getTransformedPreviewCode`. Refactor the
flow so the file contents are read once, cached, and reused to compute
`skipVitestSetupTransformation`/`skipPreviewTransformation` and to feed the
transformation helpers, avoiding duplicate `readFileSync` calls and inconsistent
reads.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 7c36610b-bcd6-430d-b1f5-3c41b996b152

📥 Commits

Reviewing files that changed from the base of the PR and between fac05a5 and 774298e.

📒 Files selected for processing (2)

• code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.test.ts
• code/lib/cli-storybook/src/automigrate/fixes/addon-a11y-addon-test.ts

[storybook-app-bot]

Package Benchmarks

^{Commit: 774298e, ran on 9 July 2026 at 10:56:37 UTC}

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

storybook

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Dependency count	73	72	🎉 -1 🎉
Self size	21.95 MB	21.94 MB	🎉 -16 KB 🎉
Dependency size	36.65 MB	36.44 MB	🎉 -213 KB 🎉
Bundle Size Analyzer	Link	Link

@storybook/cli

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Dependency count	205	204	🎉 -1 🎉
Self size	825 KB	821 KB	🎉 -4 KB 🎉
Dependency size	92.16 MB	91.93 MB	🎉 -229 KB 🎉
Bundle Size Analyzer	Link	Link

@storybook/codemod

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Dependency count	198	197	🎉 -1 🎉
Self size	32 KB	32 KB	🚨 +4 B 🚨
Dependency size	90.64 MB	90.41 MB	🎉 -229 KB 🎉
Bundle Size Analyzer	Link	Link

create-storybook

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Dependency count	74	73	🎉 -1 🎉
Self size	1.09 MB	1.09 MB	🎉 -153 B 🎉
Dependency size	58.61 MB	58.38 MB	🎉 -229 KB 🎉
Bundle Size Analyzer	node	node