[DevTools] Shrink/Deshrink Owners breadcrumbs on any resizes

[everettbu]

Mirror of facebook/react#35694
Original author: eps1lon

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Summary

We only recalculated the size when the window resizes. However, resize also happens when the inner panes are resized. Deep owner tree took up all the space since resizing wasn't possible anymore.

We use ResizeObserver now to cover all cases triggering a resize.

How did you test this change?

Before:

CleanShot.2026-02-04.at.22.55.29.mp4

After:

CleanShot.2026-02-04.at.22.48.04.mp4

[greptile-apps]

Greptile Overview

Greptile Summary

This PR updates the DevTools Hooks view breadcrumbs sizing logic to respond to layout changes beyond global window resizes by switching to a ResizeObserver. This ensures deep owner trees can reflow/shrink correctly when inner panes (not just the window) are resized, keeping the breadcrumbs usable during DevTools panel resizing.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk.
• The change is localized to the breadcrumbs sizing behavior and uses standard ResizeObserver semantics; no additional definite runtime or logic issues were found in the modified code beyond an already-reported guard needed for defaultView === null.
• packages/react-devtools-shared/src/devtools/views/hooks.js

Important Files Changed

Filename	Overview
packages/react-devtools-shared/src/devtools/views/hooks.js	Replaces window resize listener with a ResizeObserver to recalculate breadcrumbs size on any pane/element resize; no additional correctness issues found beyond the already-noted null defaultView case.

[greptile-apps]

_{3 files reviewed, 1 comment}

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[greptile-apps]

Null ownerWindow crash

container.ownerDocument.defaultView can be null (e.g. detached document, certain iframe/extension contexts). In that case ownerWindow.addEventListener('resize', ...) will throw and break the hook. Consider guarding against defaultView === null before adding/removing the listener (and still registering the pane resize listener if applicable).

Prompt To Fix With AI

This is a comment left during a code review.
Path: packages/react-devtools-shared/src/devtools/views/hooks.js
Line: 146:148

Comment:
**Null ownerWindow crash**

`container.ownerDocument.defaultView` can be `null` (e.g. detached document, certain iframe/extension contexts). In that case `ownerWindow.addEventListener('resize', ...)` will throw and break the hook. Consider guarding against `defaultView === null` before adding/removing the listener (and still registering the pane resize listener if applicable).

How can I resolve this? If you propose a fix, please make it concise.

[greptile-apps]

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[everettbu]

Upstream PR was closed or merged. Code is synced via branch mirror.