Revise RFC 0800 with learnings from implementation

[chriskrycho]

This revises the original RFC #800 with several points learned during implementation:

• Instead of implementing this RFC in terms of ember-cli-typescript, we plan to sunset it. We will write a corresponding blog post and coordinate with the CLI team about timing to finish up a transition that really began several years ago.

• We learned that keeping around the service registry is useful for integration with Owner, and implemented that in terms that make it user extensible (this needs further documentation, but is well-defined).

• We answered the unresolved questions: how to start projects, updates for blueprints, how we handle classic features, how we integrate “constructibility” as defined in RFC: Semantic Versioning for TypeScript Types #730, and how we plan (at a high level) to do side-by-side TS and JS docs.

[wagenet]

Seems generally good to me.

[simonihmig]

I have this draft PR lined up to implement the changes proposed here. While working on this and seeing the result in action two questions came up, which I am leaving here for further discussion...

[simonihmig]

for addons, emitting type declarations during build

Any idea or prescriptions how to do that exactly? With e-c-ts we have dedicated commands for this, which I believe put the .d.ts files at the root level and know how to properly clean this up again as part of postpack. Without it, will we just put a long tsc command into prepack, mostly replicating what the command does? But then how do we clean this up? Or should we put all declarations into a separate folder (we could use dist if it wasn't used already for the Ember CLI build, so maybe declarations?) and have exports and typesVersions configs in package.json point to it, similar to what v2 addons already do?

[chriskrycho]

1. I appreciate that you just solved this while I was buried in other things. 😁

2. I think the approach you landed on over at Refactor --typescript support in blueprints ember-cli/ember-cli#10283 is a good one. For other folks who haven't read that (and for posterity): the blueprint emits types into declarations and uses typesVersions to make resolution work correctly for consumers. (It also removes that after publishing.) This is probably what we would have done in the first place with ember-cli-typescript if we had had typesVersions available all those years ago.

[gitKrystan]

Per TS core meeting: @chriskrycho to check status

[chriskrycho]

Thanks to folks for (a) feedback and (b) implementing this! I think it's ready to merge, pending a review from @wagenet and/or @gitKrystan.