feat(labs): Theming (react)

[anicholls]

Summary

Spent last week working through how theming will work in Canvas Kit. This is a functional POC, but still needs some work. It also only adds theming to one existing component as a test.

Note 1: This does not have any breaking changes 🎉
Note 2: Since I've put the theming work in labs (to allow for updates to the API/theme object), we now need to depend on @workday/canvas-kit-labs-react-core if we want to start adding theming support to our components.
Note 3: This does not address CSS theming. The implementation of that is still up in the air.

Implementation

This adds a new CanvasProvider (which includes an InputProvider) that provides a theme using Emotion's ThemeProvider. You can pass a custom theme using the createCanvasTheme function:

const theme = createCanvasTheme({
  palette: {
    primary: {
      main: 'orange'
    },
  }
});
<CanvasProvider theme={theme}>
  // Components
</CanvasProvider>

createCanvasTheme will expand a partial theme into a full one based on the default theme. If you only pass a main shade, all other shades will be generated automatically based on that.

CanvasTheme also contains breakpoints (zero, s, m, l, xl) that can be accessed with the context. It also includes functions that return media queries based on the breakpoints (e.g. theme.breakpoints.up('m') will return '@media (min-width:960px)' by default).

Finally, since this is all based on React Contexts, we have an issue if anyone is not able to use contexts. This can be true for teams with multiple small React trees. To handle this, CanvasProvider can accept the setThemeGlobal prop. This sets the theme on window.wdCanvas.theme. Whenever we access the theme, we use the useTheme hook, which first looks for a context theme, then for a window theme, before falling back to the default. I added an override/wrapper to Emotion's styled function which calls useTheme behind the scenes.

Checklist

• branch has been rebased on the latest master commit
• tests are changed or added
• yarn test passes
• all (dev)dependencies that the module needs is added to its package.json
• code has been documented and, if applicable, usage described in README.md
• module has been added to canvas-kit-react and/or canvas-kit-css universal modules, if
  applicable
• design approved final implementation
• a11y approved final implementation
• code adheres to the API & Pattern guidelines

[anicholls]

CanvasProvider would provide both the theme and the input type to avoid multiple HOCs.

It would be cool if this automatically loaded the fonts module and injected the global style if a flag for that was passed as well.

[anicholls]

Note: I realized we don't have active states for our Banner component. The color/contrast gets pretty terrible based on our current system, so we should consider this.

[anicholls]

Update on the conflict with @storybook/addon-docs. I created our own theme context/provider and that still didn't resolve the issue. After a lot of fun git bisecting, I ended up needing to enforce emotion-theming@10.0.10 to keep the error away. I tried updating to the latest version of @storybook/addon-docs and that did not fix it.