migration to material-ui-pickers 2.x

[vascofg]

Won't be able to merge this until react-admin updates to @material-ui/core 3.2.0 or above, because of this:
mui/material-ui-pickers@8b35d65

This is the module that must be updated: https://github.com/marmelab/react-admin/blob/master/packages/ra-ui-materialui/package.json

[Kmaschta]

Hi there!

React Admin didn't planned to upgrade to Material UI v3 few month ago because of the the MUI team is quick to develop major versions (which include breaking changes), and our team can't follow them.
So, we waited for a more stable version to upgrade: see marmelab/react-admin#2399

As of now, the MUI team already considered a v4 with breaking changes including the styling system, React 16.8 and using the hook API.
mui/material-ui#13663

Upgrading Material UI on React Admin means a breaking change for RA. The version 2 of React Admin doesn't have one year, so it's unlikely we plan a migration for Material UI v3.

If you want to support React Admin v2, your library will have to get the Materiual UI v1.x version as a peer dependency.

Let me know if I can help you! I already planned to add this answer on the FAQ.

[vascofg]

@Kmaschta added peer-dependency on latest version