Follow up #8001 by deriving Autocomplete and LabelGroup state during render

[Copilot]

Follow-up to #8001 for the two explicitly deferred “splittable later” sites only. This narrows two mixed-responsibility effects so derivable state updates happen during render, while real side effects remain in effects.

Changelog

New

• None.

Changed

• AutocompleteMenu

  • Split close-time reordering from onOpenChange.
  • Re-sort now happens during render on the showMenu: true -> false transition using the same previous-value pattern already used in SelectPanel.
  • onOpenChange remains in useEffect as the actual side effect.

• LabelGroup

  • Numeric visibleChildCount truncation now derives visibilityMap from child indices instead of reading committed DOM state.
  • 'auto' truncation remains effect-driven via IntersectionObserver.
  • Added a shallow equality guard and memoized derived map to avoid redundant render-phase updates.

• Tests

  • Tightened Autocomplete coverage to assert onOpenChange(false -> true -> false) across open/close.
  • Added LabelGroup rerender coverage for numeric truncation updates.

Example of the render-time transition pattern used here:

const [prevShowMenu, setPrevShowMenu] = useState(showMenu)

if (prevShowMenu !== showMenu) {
  setPrevShowMenu(showMenu)

  if (prevShowMenu && showMenu === false && !sortResultMatchesState) {
    setSortedItemIds(itemIdSortResult)
  }
}

Removed

• Redundant effect-driven numeric truncation update path in LabelGroup.
• The now-unneeded set-state-in-effect / derived-state suppression around Autocomplete close-time sorting.

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

Behavior-preserving internal refactor only; no API or visual change intended.

Testing & Reviewing

Review by change site:

• Autocomplete

  • Confirm close-time sorting still happens only on open→closed transition.
  • Confirm onOpenChange still fires with the current open state and remains effect-driven.

• LabelGroup

  • Confirm numeric visibleChildCount truncation updates correctly across rerenders.
  • Confirm 'auto' truncation, inline expand/collapse, and overlay overflow behavior are unchanged.

Validated with:

• npm test -- --run packages/react/src/Autocomplete/Autocomplete.test.tsx packages/react/src/LabelGroup/LabelGroup.test.tsx
• npx eslint --max-warnings=0 packages/react/src/Autocomplete/AutocompleteMenu.tsx packages/react/src/LabelGroup/LabelGroup.tsx packages/react/src/Autocomplete/Autocomplete.test.tsx packages/react/src/LabelGroup/LabelGroup.test.tsx
• npm run type-check -w @primer/react
• npm run build
• npm test
• npm run type-check
• npm run lint
• npm run lint:css
• npm run format:diff

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-ui (Learn more about how to run integration tests)

[changeset-bot]

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Latest commit: cfb76f4

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[github-actions]

⚠️ Action required

👋 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. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

To publish a canary release for integration testing, apply the Canary Release label to this PR.

[Copilot]

Pull request overview

This PR is a follow-up refactor to #8001 that narrows two previously “splittable later” effect sites by deriving state during render for derivable transitions (while keeping real side effects in effects). The focus is Autocomplete close-time reordering and LabelGroup numeric truncation.

Changes:

• AutocompleteMenu: Track showMenu transitions during render and trigger close-time re-sorting on the open→closed transition; keep onOpenChange in an effect.
• LabelGroup: For numeric visibleChildCount, derive the truncation visibilityMap from child indices (not committed DOM) and add a shallow equality guard; keep 'auto' truncation effect-driven via IntersectionObserver.
• Tests: Strengthen coverage for onOpenChange(false → true → false) and add rerender coverage for numeric LabelGroup truncation updates.

Show a summary per file

File	Description
packages/react/src/LabelGroup/LabelGroup.tsx	Derives numeric truncation visibility from child indices and updates render path to use a cached childArray.
packages/react/src/LabelGroup/LabelGroup.test.tsx	Adds rerender assertions to ensure numeric truncation updates correctly when visibleChildCount changes.
packages/react/src/Autocomplete/AutocompleteMenu.tsx	Moves close-time sorting to a render-time transition check while keeping onOpenChange effect-driven.
packages/react/src/Autocomplete/Autocomplete.test.tsx	Tightens onOpenChange assertions to validate open/close sequencing.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 2