fix(Autocomplete.Overlay): prevent user-defined className from overriding default styles

[francinelucca]

Closes https://github.com/github/primer/issues/6289

Changelog

Changed

• Refactored AutocompleteOverlay to merge className prop with default style class
• Re-enabled and updated the Autocomplete.Overlay className test by mocking the context and using AutocompleteContext.Provider to ensure the overlay menu is shown

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 4f74127

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Patch

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Or, apply the integration-tests: skipped manually label to skip these checks.

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/9459

[primer-integration]

🔬 github-ui Integration Test Results

Check	Status	Details
CI	✅ Passed	View run
Projects (Memex)	✅ Passed	View run
VRT	✅ Passed	View run

✨ All checks passed! Your integration PR is ready for review.

[Copilot]

Pull request overview

This PR fixes a bug where user-defined className props were overriding default styles in the Autocomplete.Overlay component instead of being merged with them. The fix uses the clsx utility to properly merge CSS classes, ensuring both default and custom classes are applied.

Key changes:

• Refactored AutocompleteOverlay to merge the user-provided className prop with the default classes.Overlay class using clsx
• Re-enabled and updated the previously skipped Autocomplete.Overlay className test with proper context mocking

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/react/src/Autocomplete/AutocompleteOverlay.tsx	Added clsx import and updated className handling to merge default and custom classes
packages/react/src/Autocomplete/Autocomplete.test.tsx	Re-enabled className test with complete AutocompleteContext mock to ensure overlay is properly rendered
.changeset/dry-carrots-bathe.md	Added changeset documenting the patch-level fix