Add option to use a custom comparator for dirty state checking

[michaelmelanson]

Description

This change adds an option to the useField hook in react-form to use a custom comparator for checking whether a field is dirty. This allows you to, for example, apply a deep equals function for deep equality checking if you field requires it:

  const myField = useField<Type>({
    value: initialValue,
    validates: () => false,
    dirtyStateComparator: _.isEqual
  });

This is required to resolve a bug we have an in upcoming Web feature (Slack me for more details) where we are storing a list of objects in a field, and currently we remain in the dirty state if the user manually resets the form to its default state. With this feature, we correctly detect that the form is again in its default state, and report that it's now clean.

Note: I recommend turning on "Hide whitespace changes" when reviewing this feature to make the diff readable.

Type of change

• react-form Minor: New feature (non-breaking change which adds functionality)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above

[marutypes]

One implementation question, otherwise looks good

[patsissons]

just a few suggestions for minor tweaks from me, changes overall make sense.

[patsissons]

this and the shallowFieldReducer feel like they may belong somewhere else?

[michaelmelanson]

It feels like that to me too, but I just tried moving it out of that file and couldn't find a place that felt right because the call to makeFieldReducer would have to call back here anyway. 😕

[patsissons]

LGTM