[ShadyCSS] Improve transparency and remove need to use custom API from ShadyCSS

[dfreedm]

ShadyCSS v1 has a lot of limitations that keep hitting users right in the face.

It's time to fix that, and make ShadyCSS totally (mostly) transparent.

Current API should probably stay the same, but will become entirely optional performance enhancements. However, the behavior change is probably enough to warrant a breaking change.

Enhancements:

• Automatically handle top-level styles
  • No more need for <custom-style> or CustomStyleInterface
• Let arbitrary elements like <div> have scoped shadowroots
  • Only custom elements are supported right now
• Handle multiple stylesheets
  • Better for everyone!
• Make ::slotted work better
  • Handle redistribution sanely
  • Remove as many of the weird corner cases with the current scheme as possible
• Handle dynamic changes to # of stylesheets
  • Scope the root based on the ordered set of stylesheets contained in the root

[abdonrd]

Any opinions about drop the @apply shim?

[OmidHekayati]

Why continue use of @apply || mixin spec when it is obsolete!!! and never get standard:
http://www.xanthir.com/b4o00
This spec isn't yet approved by the relevant Working Group:
https://tabatkins.github.io/specs/css-apply-rule/
and I think never approve by any browsers. Chrome close related issue:
https://www.chromestatus.com/feature/5753701012602880

[dfreedm]

@abdonrd @OmidHekayati Dropping the @apply shim is definitely something I want to do, but I want to have a few deprecation cycles before removing it completely. The improvements I want to make to ShadyCSS will still be beneficial to Polymer 2 users, where @apply is still supported.

That said, as soon as ::part or an equivalent is specced, I could be more amenable to a rapid deprecation of @apply

[OmidHekayati]

@azakus
The one downside of ::part() is that it only works for shadow DOM
I think it is better to announcement in shadycss readme that @apply will never be specced and developers must have plan to change usage of it.

[abdonrd]

@azakus thanks! ::part or an equivalent would be really great!

[tomalec]

Are there any news, plans or estimates for this issue? The issues with lack of API (and build in support) for different shadow DOM for native and custom elements are still effectively blocking us to migrate to V1 :(

I could try to prepare some PRs for extending this PR, but I'm not sure if you even consider them given, planned refactoring.

[equinusocio]

Any update? :D

[haugthom]

+1

[abdonrd]

@azakus #125 close this issue...? 🤔

[dfreedm]

Whoops, that's weird

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.