Focus on TextField is lost if variant is changed on the fly

[keul]

• The issue is present in the latest release.
• I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

If the variant property of a TextField is changed on the fly the focus on the field is lost

Expected Behavior 🤔

Would be nice if focus is kept.

Steps to Reproduce 🕹

Go to https://odtfp.csb.app/

1. type something in the field
2. ...then type an _ char (which enable the error state)
3. ...see focus being lost
4. re-focus the field manually
5. remove the _ (so exit the "error state"
6. focus is lost again

Context 🔦

What I was trying to achieve is to have a better highlight of the field error so I'm switching from "standard" to "filled" variant on the fly in case of error.

I perfectly know that I can have the same visual behavior just using styles, and I'm going in this direction, but I was not sure if this should be threat as a minor bug or not, so I'm reporting this.

Your Environment 🌎

Tech	Version
Material-UI	v4.9.9
React	16.12.0

[oliviertassinari]

@keul Thanks for the report, however, I don't think that we want to support this use case. It will increase the bundle size and distract us from more important problems.

[oliviertassinari]

@marcosvega91 Regarding your proposed fix, it makes me think of #14132.

[marcosvega91]

I proposed a fix that if i think better has not sense. So I deleted It.

We can check if the variant is changed and the input has the current focus and trigger focus on the element on next render, but i think Is only a workaround and not a solution

[eps1lon]

I think for uncontrolled components the state would be lost as well. It would definitely be nice to be able to switch variants but the amount of work required isn't justified compared to the gain. Generally you don't switch variants since you only have a single variant per form anyway.

[keul]

@eps1lon @oliviertassinari I updated the codesandox with an uncontrolled example and there's the same issue.
However I really don't find useful adding any complexity for supporting this edge case.
My report was only just in case it was hiding other issues. Changing the variant on the fly is not useful.

Thanks all for your time!