TypeInfo: Should use readonly types over mutable types.

The material-ui components declare their types as mutable when in fact they are treated as immutable by material-ui.

• 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 😯

Values of a readonly type cannot be given to material-ui components.

I’ve only checked this with the Autocomplete component but I assume there are probably other components affected by this same issue.

Expected Behavior 🤔

Values of a readonly type should be able to be given to material-ui components.

Steps to Reproduce 🕹

Issue demonstrated here codesandbox.io/s/funny-sky-mw1st in the src/App.tsx file. The prop options cannot be assigned a readonly type.

Steps:

1. Create a variable of a Readonly type.
2. Supply that variable to a material-ui component that is expecting a mutable type.

Context 🔦

I’m trying to have a fully immutable and function code base using the linting rules defined in eslint-plugin-functional.

Your Environment 🌎

Tech	Version
Material-UI core	v4.9.7
Material-UI lab	v4.0.0-alpha.46
React	v16.13.0
TypeScript	v3.8.3

[eps1lon]

I get the desire to make this more strict and in the end this might as well not break anything. It’s just that I want to avoid different typing approaches across the code base which means we would update types for components that are considered stable. Looking at how much value this provides even a single issue report isn’t worth the trouble for us.

But who knows. Maybe this gets traction. Thanks for the quality issue anyway. Always appreciated 👍

[eps1lon]

This would throw now, no?

const values: AutoCompleteProps['values'] = []
values.push(1)