Material-ui: Default theme overwriting custom theme when inserting material components into dom tree directly

[owzh]

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

Current Behavior 😯

When rendering Material components with ReactDOM.unstable_renderSubtreeIntoContainer(), custom theme is not being carried forward and it's propagating the default theme instead.

We are using a couple third party libraries that are not using React and we have to step outside of React ecosystem to pass in components that we wanted to render. Before, we didn't have any issues getting Material components to style correctly in these. After upgrading to v4.4.3, whenever we open up such a hybrid component, it injects the default theme into the dom tree and overrides our customized theme.

This is what we see in the console when logging the children components that we passed in.

Expected Behavior 🤔

Custom theme info should be forwarded with Material components when using unstable_renderSubtreeIntoContainer or a similar function.

Steps to Reproduce 🕹

https://codesandbox.io/s/practical-pine-ytx5z

| Tech | Version |
| ----------- | ------- |
| Material-UI | v4.4.3 |
| React | v16.9.0 |

[oliviertassinari]

I propose we close the issue as "won't fix" per https://github.com/facebook/react/issues/10143.

[oliviertassinari]

We are using a couple third party libraries that are not using React and we have to step outside of React ecosystem to pass in components that we wanted to render.

Can we learn more about them? :)

[owzh]

let me see if i can replicate it with createPortal which is supposed to be what we need to migrate to for unstable_renderSubtreeIntoContainer.

[owzh]

ok, not an issue with createPortal.

[oliviertassinari]

Thanks for double-checking, the context propagation might work with Material-UI v3 as using the legacy context API.