Clarify how to set `enableTypeScriptTransform` in Ember apps, addons and engines

[ijlee2]

Description

Currently, the README explains how to set enableTypeScriptTransform for Ember apps only.

It wasn't clear to me what to do for Ember addons and engines (to be precise, engines created as an addon). The setup for engines turned out to be tricky, because I wasn't supposed to embed the 'ember-cli-babel' key inside of an options hash (the pattern suggested by apps and addons).

I'd like to update the section Enabling TypeScript Transpilation so that:

• A developer can copy-paste the code example.
• The code examples closely match the latest Ember blueprint (v4.9.0-beta.0 at the time of writing). (Note, I continued to write return app.toTree();. That is, to limit the scope of this pull request, I didn't assume that the developer uses, or will use, Embroider.)
• The surrounding texts have shorter sentences and are easier to understand. (The change may help those whose native language is not English.)

[ijlee2]

@chriskrycho When ember-cli-typescript is installed in a v1 addon, two scripts get added to package.json:

{
  "scripts": {
    "prepack": "ember ts:precompile",
    "postpack": "ember ts:clean"
  }
}

When we use enableTypeScriptTransform and uninstall ember-cli-typescript, is it okay to remove these two scripts (i.e. the addon and its types will be published without an issue)?

If so, I wonder if this is worth mentioning in ember-cli-babel's README. I can also see the perspective that it may fit better in a migration guide in the ember-cli-typescript repo.

[chriskrycho]

Nope, nothing will generate types out of the box for you in that mode. For that reason, addons which want to publish types should generally do one of two things:

• Classic addons should continue to use ember-cli-typescript.
• Modern/Embroider addons should use the TS-ready rollup config for addons that @simonihmig and others built, which will publish types correctly.

Probably worth documenting that explicitly here (feel free to steal that prose and tweak/improve it!).

[backspace]

Thanks for writing this up, it helped me when I was having build problems with an addon. I think it would be great to have merged so it’s easier to find 😀

[ijlee2]

@bertdeblock Could we merge this pull request some time soon? (I forget where we had left off, if there had been additional feedback that I needed to address.)