perf(SelectPanel): reset intermediate selection during render, not in an effect

[mattcosta7]

Overview

SelectPanel reset the single-select modal's intermediate selection from an effect:

useEffect(() => {
  setIntermediateSelected(isSingleSelectModal ? selected : undefined)
}, [isSingleSelectModal, open, selected])

That's the set-state-in-effect / no-derived-state pattern and forces an extra post-commit render whenever the panel opens/closes or the selection changes. This replaces it with the adjust-state-during-render pattern (tracking the previous inputs), which React restarts before committing — so the reset is behavior-identical with no extra commit:

const [prev, setPrev] = useState({open, selected, isSingleSelectModal})
if (prev.open !== open || prev.selected !== selected || prev.isSingleSelectModal !== isSingleSelectModal) {
  setPrev({open, selected, isSingleSelectModal})
  setIntermediateSelected(isSingleSelectModal ? selected : undefined)
}

Removing the eslint-disable also lets the lint rule guard against regressions.

Changelog

Changed

• SelectPanel: the single-select modal's intermediate selection is reset during render instead of in an effect, avoiding an extra re-render on open/close/selection change. No behavior or API change.

Rollout strategy

• Patch release
• Minor release
• Major release
• None

Testing & Reviewing

• Behavior is identical to the previous effect (same {open, selected, isSingleSelectModal} reset triggers).
• The full SelectPanel suite (152 tests), which covers the single-select-modal intermediate-selection / cancel / confirm flows, passes unchanged.

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

[changeset-bot]

🦋 Changeset detected

Latest commit: 50046a3

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

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]

⚠️ 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. If this doesn't work, you can also use the original workflow here. 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 updates SelectPanel’s single-select modal behavior to reset the intermediate selection during render (tracking prior inputs) instead of syncing it from a useEffect, aiming to avoid an extra post-commit render and removing the related ESLint disable.

Changes:

• Replace the useEffect-based intermediate-selection reset with an adjust-state-during-render approach keyed on {open, selected, isSingleSelectModal} changes.
• Add a patch changeset describing the performance-oriented internal behavior adjustment.

Show a summary per file

File	Description
packages/react/src/SelectPanel/SelectPanel.tsx	Moves intermediate selection reset logic from an effect to render-time adjustment based on previous inputs.
.changeset/selectpanel-intermediate-selected-derive.md	Adds a patch changeset documenting the internal behavior/perf change.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1

[Copilot]

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Low

[primer-integration]

Integration test results from github/github-ui PR:

  CI Passed
  VRT Running
  Projects Waiting

[Copilot]

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 0 new
• Review effort level: Low