fix(ui): prevent hidden Tabs tree from stomping active indicator opacity

React Aria's `CollectionBuilder` renders `TabList`'s children into both a
hidden collection-building tree and the real DOM. The hidden instance of
`TabsIndicators` sits outside the `TabListStateContext` provider, so its
`state` is `null` — causing its `updateCSSVariables` effect to hit the
`else` branch and write `--active-tab-opacity: 0` to the `tabsRef` DOM
element that the real instance also writes to. Under the right render
ordering, this hidden write lands after the real instance's `opacity: 1`
and makes the active indicator disappear on uncontrolled Tabs.

Guard `updateCSSVariables` with an early return when `state == null` so
the hidden instance never writes to the shared DOM element.

Signed-off-by: Johan Persson <johanopersson@gmail.com>

This commit is contained in:

Johan Persson

2026-04-17 13:43:54 +02:00

parent 64b186f465

commit c6fc76f532

2 changed files with 13 additions and 0 deletions

									
										.changeset/fix-tabs-active-indicator-disappearing.md
									
		+7
		
												View File
												
				@@ -0,0 +1,7 @@

				---

				'@backstage/ui': patch

				---

				Fixed an issue where the active tab indicator would disappear shortly after page load for uncontrolled Tabs.

				**Affected components:** Tabs