Rendering bug in either descendants or react

🐛 Bug report

Current Behavior

I might of setup my test case wrong, but I think its right.

I’ve written tests for React Testing Library as well as a helper to check if the bug is present.

5% of the time the descendants code will register the wrong indexes.

Expected behavior

no indexes to be wrong.

Reproducible example

CodeSandbox Example GitHub Source

Suggested solution(s)

again, not sure what the issue is here, and quite possibly could be a bug in react.

Additional context

You can run the example app locally, and use this code to mimic the test I have written.

function testcase() {
    document.querySelector('button').click();
    Array.from(document.querySelectorAll('span')).forEach(el => {
      console.assert(el.textContent.endsWith(el.parentElement.getAttribute('data-index')))
    })
}

// once testcase is defined in the console, call this {n} times till you see the assert error.

testcase();

Your environment

Software	Name(s)	Version
Reach Package	descendants	0.15.3
React	react	17.0.2
Browser	chrome	92.0.4515.107
Assistive tech	N/A
Node	node	14.17.3
npm/yarn	npm	7.20.1
Operating System	Zorin OS Linux	16

[chaance]

Closing because I think I found and fixed the bug, but I added a note to the release to explain the potential unexpected issues you might encounter along the way. Descendants are only registered/unregistered when new items enter/leave the list but not when existing items move around.

[chaance]

The good news: I do believe you found a bug, and I think it should be fixed in the next release. Thanks for that! It’ll change some of our APIs a bit and require a little more boilerplate in the consumer packages, but this is technically an internal package so I’m not super concerned about that.

That said, even with the fix, I’m not sure it’ll work for your use case here. I don’t know that we need that sort of descendant nesting you’re going for. If you can get it to work consistently and keep things performant I’ll be happy to take a PR, but just as a disclaimer it’s possible that we keep changing things indiscriminately without regards to semver, so I might still fork it or try your own solution if you’re currently using it directly.