[BUG] Wrong startIndex and endIndex rangeChanged callback in GroupedVirtuoso component

Describe the bug Using GroupedVirtuoso with rangeChanged callback, the range startIndex and endIndex returned by the function sometimes emit wrong values.

i have this summarized implementation:

<GroupedVirtuoso
          data={users}
          style={{ height: 200 }}
          groupCounts={[500, 500]}
          rangeChanged={(range) => console.log(range)}
          ref={virtuoso}
          itemContent={(index, _, user) => {
            return (
              <div {...item} />
            );
          }}
        />

Reproduction https://codesandbox.io/s/sandpack-project-forked-i1hkpv?file=/App.js

To Reproduce Steps to reproduce the behavior:

1. Click on ‘Scroll to 500’
2. See the log of the rangeChanged callback
3. If everything is normal, then scroll the list up and down

Expected behavior I think the expected behavior is the rangeChanged emit only indexes that the list is rendering on the screen. And the startIndex cannot be greater than endIndex. For example, in the image below:

• First log: The startIndex: 497 and endIndex: 1 should never happens because it endIndex cannot be smaller than startIndex
• Last log: The startIndex: 1 and endIndex: 502 should not be printed because all of this items list is not being rendered at this time.

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu Linux
• Browser: Chrome

[petyosi]

Great. Fork the repo, push your branch there, and GH should suggest the way: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork

[petyosi]

Confirming that, it’s a weird bug. I will look into it.