chore(SegmentedControl): Remove the CSS modules feature flag from the SegmentedControl component

[jonrohan]

Closes https://github.com/github/primer/issues/3917

Changelog

New

Changed

Removed

Remove the CSS modules feature flag from the SegmentedControl component

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

Shouldn't have any visual effect on production.

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: fe97485

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	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	96 KB (-0.59% 🔽)
packages/react/dist/browser.umd.js	96.2 KB (-0.66% 🔽)

[primer-integration]

👋 Hi from github/github! Your integration PR is ready: https://github.com/github/github/pull/377284

[primer-integration]

🟢 golden-jobs completed with status success.

[Copilot]

Pull Request Overview

This PR removes the legacy CSS modules feature flag and styled-components toggles from the SegmentedControl suite, consolidating all styling in CSS modules and the BoxWithFallback component.

• Eliminated the getSegmentedControlStyles file and its related feature flag.
• Replaced all toggleStyledComponent and styled usages in SegmentedControl, SegmentedControlButton, and SegmentedControlIconButton with BoxWithFallback and CSS module classes.
• Updated CSS to include a new .LeadingIcon rule for consistent icon spacing.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/react/src/SegmentedControl/getSegmentedControlStyles.ts	Deleted—removed the old style generator and feature flag.
packages/react/src/SegmentedControl/SegmentedControlIconButton.tsx	Swapped styled-component logic for BoxWithFallback + CSS modules.
packages/react/src/SegmentedControl/SegmentedControlButton.tsx	Swapped styled-component logic for BoxWithFallback + CSS modules.
packages/react/src/SegmentedControl/SegmentedControl.tsx	Replaced the toggled ul and inline styles with BoxWithFallback.
packages/react/src/SegmentedControl/SegmentedControl.module.css	Added .LeadingIcon for icon margin.
.changeset/chilled-camels-obey.md	Added changeset for minor release.

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!