[preview card] Keep inline preview anchored while open

[atomiks]

The React Compiler browser CI exposed a multiline Preview Card test that expected the popup to move to a newly entered line while it was already open. Keeping the opened anchor stable is less disorienting; a new line is only used when opening or reopening.

https://deploy-preview-4836--base-ui.netlify.app/experiments/inline-positioning

With delay enabled, it won't choose a new rect while open. Matches Wikipedia

Root cause

Inline hover coordinates were refreshed on same-trigger mouseenter while open, so incidental positioning updates could make the popup jump.

Changes

• Keep stored inline coordinates unchanged while the preview card is open.
• Update the multiline trigger test to assert stable positioning while open.

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@4836
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@4836
  

commit: 4a86709

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	0B(0.00%)	🔺+1B(0.00%)

Details of bundle changes

Performance

Total duration: 1,068.25 ms -104.27 ms^(-8.9%) | Renders: 50 ⁽⁺⁰⁾ | Paint: 1,635.05 ms -192.39 ms^(-10.5%)

No significant changes — details

---

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

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[michaldudak]

Codex Review (GPT-5.5)

I reviewed PR 4836 as a bug-fix against freshly fetched upstream/master. The implementation change is narrowly scoped and matches the stated root cause, but one updated browser regression test does not actually guard the old user-facing failure.

1. Bugs / Issues

1. 🟡 Browser regression test still false-passes against the old behavior (non-blocking)

packages/react/src/preview-card/positioner/PreviewCardPositioner.test.tsx

await user.pointer([
  { target: document.body },
  {
    target: trigger,
    coords: {
      clientX: secondLineRect.left + secondLineRect.width / 2,
      clientY: secondLineRect.top + secondLineRect.height / 2,
    },
  },
]);

expectWithin(positioner.getBoundingClientRect().y, firstLineRect.bottom + 5);

The old implementation updates inlineRectCoordsRef on same-trigger mouseenter, but the visible jump only appears after a later positioning update. I verified the PR’s updated browser test still passes when paired with the old inlineRect.ts behavior, while the helper-level inlineRect test fails as expected. That means the browser test can pass before the regression has a chance to manifest.

Fix: After entering the second line, force or wait for the same positioning update path that exposed the jump, then assert the position still tracks firstLineRect.

Root Cause & Patch Assessment

The code change itself is sound: onMouseEnter now uses the same “only while closed” guard as onMouseMove, so the opened trigger’s captured inline rect remains stable. Passing isOpenedByThisTrigger rather than global open state also preserves trigger switching and close-transition re-entry behavior.

Test Coverage Assessment

I ran:

pnpm test:jsdom inlineRect --no-watch
pnpm test:chromium PreviewCardPositioner --no-watch

Both passed on the PR branch. I also checked regression sensitivity against the old implementation: the updated helper test fails as expected, but the updated browser test still passes, which is the coverage gap above.

Recommendation

Approve after nits are addressed 🟡

The runtime fix looks correct, and the helper regression coverage is meaningful. I’d tighten the browser test before merging so the user-facing Preview Card behavior is protected too.

[atomiks]

Code Review (GPT-5.5)

Approve ✅ because the inline-rect change matches the intended stable-open behavior, keeps reopen/new-trigger paths intact, and the targeted regression coverage passes.

1. Bugs / Issues (None)

Root Cause & Patch Assessment

The fix is appropriately narrow: getInlineRectTriggerProps now gates both React onMouseEnter and onMouseMove coordinate refreshes while that trigger is already open, so incidental same-trigger re-entry no longer moves the popup to a different wrapped line.

The existing native updateInlineRectCoords path remains available for hover-open handling, and other triggers can still capture coordinates because isOpenedByThisTrigger is scoped per trigger.

Test Coverage Assessment

Validated against a freshly fetched upstream/master diff.

Ran:

pnpm test:jsdom inlineRect --no-watch
pnpm test:chromium PreviewCardPositioner --no-watch

Both passed. I did not separately execute the updated regression test against base-only source, but by inspection the previous onMouseEnter: updateCoords path is the behavior this test now guards against.