perf(FormControl): derive validation message visibility during render

[mattcosta7]

Overview

ValidationAnimationContainer (used by FormControl to animate validation messages) tracked whether to render its children in state and synced it from an effect:

useEffect(() => { if (show) setRender(true) }, [show])

That's the set-state-in-effect / no-derived-state pattern, and it deferred the enter animation by one render. This adjusts the state during render instead, so the content mounts in the same commit:

const [shouldRender, setShouldRender] = useState(show)
if (show && !shouldRender) setShouldRender(true)          // enter, in render
const onAnimationEnd = () => { if (!show) setShouldRender(false) } // exit unchanged

Behavior is identical (the exit animation still plays via onAnimationEnd), but there's no extra post-commit render, and removing the eslint-disable lets the lint rule guard against regressions.

Changelog

Changed

• FormControl validation messages now render in the same commit instead of one render later (internal ValidationAnimationContainer refactor). No public API change.

Rollout strategy

• Patch release
• Minor release
• Major release
• None

Testing & Reviewing

• Added a render-count regression test (via createRenderCounter) asserting show produces no extra update commit.
• The FormControl suite 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: 0a85edd

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.

[primer]

🤖 Lint issues have been automatically fixed and committed to this PR.

[Copilot]

Pull request overview

This PR refactors the internal ValidationAnimationContainer used by FormControl-adjacent validation UI to avoid an effect-driven “derived state” update, aiming to mount validation content in the same commit when show becomes true.

Changes:

• Refactored ValidationAnimationContainer to set shouldRender when show becomes true during render (removing the effect + eslint-disable).
• Added a dedicated unit test suite, including a render-count regression assertion.
• Added a patch changeset and updated the classname-test script ignore list for the new test file.

Show a summary per file

File	Description
script/check-classname-tests.mjs	Ignores the new internal component test from the “implementsClassName” enforcement script.
packages/react/src/internal/components/ValidationAnimationContainer.tsx	Removes effect-driven derived state and derives “enter” visibility during render.
packages/react/src/internal/components/ValidationAnimationContainer.test.tsx	Adds initial render/transition tests and a render-count regression test.
.changeset/validation-animation-derive-in-render.md	Adds a patch changeset entry for the behavior/perf improvement.

Copilot's findings

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

[Copilot]

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Low

[primer-integration]

Integration test results from github/github-ui PR:

  CI Passed
  VRT Waiting
  Projects Running

[mattcosta7]

npm packages integration test for #8023 github/github-ui#25916

these all passed?