implementing rfc931

[ef4]

Edited to add: the call signature in the RFC has changed, this PR needs updating to that new call signature.

This implements emberjs/rfcs#931, which defines a stable low-level representation for template tags.

When using targetFormat: 'hbs' it acts as a polyfill for the ahead-of-time compiler as described in the RFC, using only stable public APIs. Assuming the RFC is approved and implemented, this implementation could change so it leaves template() alone, rather than replacing it with precompileTemplate and setComponentTemplate.

When using targetFormat: 'wire' it's not really a polyfill, since this package is the definitive implementation.

There are skipped tests to cover cases that are important but will depend on glimmerjs/glimmer-vm#1421

• targetFormat: 'wire' with explicit form
• targetFormat: 'hbs' with explicit form
• targetFormat: 'wire' with implicit form
• targetFormat: 'hbs' with implicit form
• end-to-end test with ef4/content-tag

[achambers]

Had a crack at reviewing this against the RFC and it looks good to me. Left 2 comments/questions there for consideration. But overall, LGTM

[achambers]

@ef4 Pretty sure this shouldn't here. ✂️

[achambers]

Looking at the RFC to reconcile this implementation and it got me wondering, is there value in a test that shows using the instance arg that's passed in to the scope function, say, for accessing private fields?

This is the code that got me wondering this:

// in class member position, we can also put private fields in scope
class extends Component {
  static {
    template(
      "<Section @title={{this.title}} @subhead={{this.#secret}} />", 
      {
        component: this,
        scope: (instance) => ({ 
          Section, 
          "#secret": instance.#secret
        }),
      },
    )
  }
}