Side effects in `useMemo` in `useRowSelect` plugin

I decided to pull this out of #2120 to give it proper focus, and also because if 2120 gets resolved in another way, I believe it is still important to see this fixed.

Describe the bug (required)

The useRowSelect plugins incurs side effects in a useMemo call.

This violates the useMemo pattern, and is the probable root cause for varied desynchronization and re-rendering rendering issues (eg #2159, #2120).

Provide an example via Codesandbox! (required)

See related bugs. Perhaps this is the simplest form, though its simplicity needs React.Strict to trigger a break.

In more complex code, it manifests itself as isSelected/selectedFlatRows desynchronization.

Steps To Reproduce

• Go to useRowSelect.js:181.
• Notice the lines that have side effects.

    row.isSelected = !!isSelected
    row.isSomeSelected = isSelected === null
  

Expected behavior

I see two possible approaches:

• Better: properly derive isSelected from selectedRowIds (that is, make isSelected a useMemo with dependency on selectedRowIds)
• Alternative: explore useLayoutEffect instead? Sounds kludgy.

[tannerlinsley]

The amount of people running into this as of today are very few, and seeing how the issue will disappear in the next version, I don’t see a big pressing issue to fix this. That said, if the number of people experiencing this issue increases dramatically I will look into fixing it in v7. As always anyone coming across the this issue that wants to fix it is more than welcome to open a PR and I would be happy to guide them along the way.

[alverdal]

I ran into this issue today as well, was quite confused until I found this issue. perhaps it could be mentioned in documentation as a known issue until it’s fixed?