[navigation menu] Preserve exit transition when controlled

[mattrothenberg]

Problem

When NavigationMenu is controlled, consumers can close it by updating value to null directly. That prop-driven close does not go through the same internal setValue(null, eventDetails) path used by interactions like hover-out, so the popup dimensions may be measured after active content has already started unmounting. In that case the popup can collapse immediately, making the data-ending-style exit transition appear to be skipped.

Reproduction

Working

https://stackblitz.com/edit/vitejs-vite-czwevbev?file=src%2FApp.tsx

Solution

• snapshot the current popup and positioner dimensions when an open controlled NavigationMenu commits to closing
• reuse the existing fixed-size CSS variables used by the internal interaction close path
• keep the change internal to NavigationMenu without adding a new public API
• add a regression test for externally setting the controlled value to null while the popup exits
• add a public controlled-close docs demo for visual verification

Testing

• pnpm vitest run packages/react/src/navigation-menu/root/NavigationMenuRoot.test.tsx --project @base-ui/react
• pnpm --filter docs typescript
• Manually verified the docs demo at /react/components/navigation-menu: unchecking "Menu open" applies data-ending-style with frozen popup dimensions

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@4855
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@4855
  

commit: 3e34463

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	🔺+29B(+0.01%)	🔺+57B(+0.04%)

Details of bundle changes

Performance

Total duration: 1,296.03 ms +114.84 ms^(+9.7%) | Renders: 50 ⁽⁺⁰⁾ | Paint: 1,962.57 ms +130.00 ms^(+7.1%)

Test	Duration	Renders
Menu mount (300 instances)	152.01 ms 🔺+28.76 ms(+23.3%)	2 (+0)
Mixed surface mount (app-like density)	93.46 ms 🔺+20.35 ms(+27.8%)	5 (+0)
Scroll Area mount (300 instances)	98.54 ms 🔺+17.72 ms(+21.9%)	3 (+0)
Select open (500 options)	51.78 ms 🔺+12.78 ms(+32.8%)	14 (+0)

8 tests within noise — details

---

Check out the code infra dashboard for more information about this PR.

[netlify]

✅ Deploy Preview for base-ui ready!

Name	Link
🔨 Latest commit	3e34463
🔍 Latest deploy log	https://app.netlify.com/projects/base-ui/deploys/6a100e0efe45d00008b84c62
😎 Deploy Preview	https://deploy-preview-4855--base-ui.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
🤖 Make changes	Run an agent on this branch

---

To edit notification comments on pull requests, go to your Netlify project configuration.