React 16.13.X warning when Field has validator

[yann-combarnous]

Are you submitting a bug report or a feature request?

Bug report

What is the current behavior?

https://codesandbox.io/s/react-1613x-final-form-array-yfcmx

Instructions:

• Click on "Show username" checkbox
• Watch console error

Warning: Cannot update a component (`ReactFinalForm`) while rendering a different component (`Field`). To locate the bad setState() call inside `Field`, follow the stack trace as described in https://fb.me/setstate-in-render
    in Field (at MyFieldArray.js:12)
    in FieldArray (at MyFieldArray.js:6)
    in MyFieldArray (at App.js:30)
    in form (at App.js:20)
    in ReactFinalForm (at App.js:12)
    in div (at App.js:11)
    in App (at src/index.js:7)

What is the expected behavior?

No console warning

Sandbox Link

What's your environment?

Latest React final form 6.4.0 and latest final form library 4.19, see codesandbox

Other information

[yann-combarnous]

See offending code at #751 (comment)

[erikras]

Published fix in final-form@4.19.1.

[zaguiini]

The problem is happening on 4.20.1. Was the fix reverted by any chance?

I'm using the useField hook.