Features & Fixes: DOM in core, less DOM writes, N Composition,

[jonathantneal]

This PR would introduce the following changes:

• Fixed issues composing together and passing along variants, compoundVariants, and defaultVariants.
• Reduced how often the DOM is modified without reducing how quickly it is updated.
• Added DOM injection to core.
• Added the ability to create a component extended from an unlimited number of other components.
• Changed the theme function to return an object instead of another function.

PR Goals

• Resolves Variants and css prop styles do not apply #441
• Resolves @stitches/core should handle injection/hydration of styles #440
• Resolves Theme function not returning class name when using css API #436
• Resolves [0.1.0-canary.12] Compound variants do not apply to composed components #431
• Resolves [0.1.0-canary.x] Pass variants as props to wrapped components #416
• Resolves [stitches/core] css should accept n compositions #397

[codesandbox-ci]

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Latest deployment of this branch, based on commit 2f211a1:

Sandbox	Source
Stitches CI: CRA	Configuration
Stitches CI: Next.js	Configuration
Stitches: pass variants down to wrapped component	Issue #416
eloquent-mcnulty-up1de	Issue #431
Stitches Theme difference between APIs - Styled Version	Issue #436
Stitches Theme difference between APIs - CSS Version	Issue #436
stitches bug	Issue #441

[peduarte]

🔥

[jonathantneal]

I’ve removed #448 from the goals of this PR, because like #449 the issue acknowledges that there isn’t an obvious problem or solution to address, neither inside or outside of Stitches.

[arempe93]

hey @jonathantneal -- tried this branch in my project since it should fix #431, discovered a bug with defaultVariants and composed components

https://codesandbox.io/s/default-variants-bug-11qbb
TypeError: Cannot read property 'undefined' of undefined

I tracked it down to this line here:

https://github.com/modulz/stitches/blob/be2734e7e1ed7ddf00865c8d28855025beabd70b/packages/core/src/index.js#L243

because variantProps[defaultVariantName] could be undefined. So may be a simple fix to guard that, but I'm not aware of the potential second order effects with all the changes.

[jonathantneal]

@arempe93, thank you 🙏! Slipped the fix into #456