[core] Remove withTheme from @material-ui/core

[mnajdova]

• The withTheme utility has been removed from the @material-ui/core/styles package. You can use the @material-ui/styles/withTheme instead. Make sure to add a ThemeProvider at the root of your application, as the defaultTheme is no longer available. If you are using this utility together with @material-ui/core, it's recommended you use the ThemeProvider from @material-ui/core/styles instead.

   import * as React from 'react';
  -import { withTheme } from '@material-ui/core/styles';
  +import { withTheme } from '@material-ui/styles';
  +import { createTheme, ThemeProvider } from '@material-ui/core/styles';
    
  +const theme = createTheme();
   const MyComponent = withTheme(({ theme }) => <div>{props.theme.direction}</div>);
  
   function App(props) {
  -  return <MyComponent />;
  +  return <ThemeProvider theme={theme}><MyComponent {...props} /></ThemeProvider>;
   }

---

One of the PRs that is necessary for removing @material-ui/styles as a dependency of @material-ui/core.

[mui-pr-bot]

Details of bundle changes

Generated by 🚫 dangerJS against 03ab006

[mnajdova]

There are tests for this in the @material-ui/styles package.

[eps1lon]

Did we intend to keep withTheme at all considering useTheme exists?

[oliviertassinari]

I was wondering too. It makes sense for the legacy code that can't be migrated to hooks, no preferences.

[mnajdova]

I wasn't thinking too much about it to be honest, I am just trying to break the dependencies to @material-ui/styles at this stage.

[oliviertassinari]

@mnajdova I think that we need to resolve the question of Sebastian. I see two cases based on the answer:

1. If we estimate that it's still too early to drop the HOC API, then it seems that the best course is to follow what we do with useTheme().
2. If we estimate that it's time to introduce a breaking change and drop withTheme for v5 users (it wasn't planned in [RFC] Material-UI v5 🚀 #20012 but why not), then I think that the current state of the PR is OK.

[eps1lon]

Isn't it just a prop-injector that injects useTheme? That seems trivial enough to fork if you really need it. And in turn we can cut down in shipped code.

[mnajdova]

@mnajdova I think that we need to resolve the question of Sebastian. I see two cases based on the answer:

• If we estimate that it's still too early to drop the HOC API, then it seems that the best course is to follow what we do with useTheme().
• If we estimate that it's time to introduce a breaking change and drop withTheme for v5 users (it wasn't planned in [RFC] Material-UI v5 🚀 #20012 but why not), then I think that the current state of the PR is OK.

Let's go with option 2. I wouldn't drop anything from @material-ui/styles, as we are anyway going to deprecate that package, so I don't think it's worth doing too many changes there. If you disagree, we can go trough everything exported from @material-ui/styles and see whether we can drop some things.

[oliviertassinari]

@mnajdova Happy with option 2. The only reason I raised 1 is because of https://styled-components.com/docs/api#withtheme and https://emotion.sh/docs/theming#withthemecomponent-reactcomponenttype-reactcomponenttype.