Feature: allowAppImports

[mansona]

This is taking over from #586 👍

Fixes #565
Fixes #158

[ef4]

TODO list items:

• filtering matching files out of classic build pipeline. May involve monkey-patching the appInstance's trees.app.
• teaching the splitter to emit imports for package-name-prefixed imports that match, like "my-app/lib/example1".
• teaching the splitter to emit imports for relative imports for files that match, like "../lib/example1"
• handling webpack externals so that when an auto-imported module imports a classically-built app module it doesn't get duplicated inside webpack. This is an extension to what we already do to support v2 addons using ember-provided features.
• make babel-loader config sensitive to the fact that app code gets the full app babel config (whereas dependencies get a streamlined, standardized config)
• make sure that the dynamic imports work as well as the static-imports test scenario

[simonihmig]

I discussed this feature a while ago with @ef4 within CrowdStrike, and IIRC we came to the conclusion that also addons should be able to do this. Example use case would be to have a v1 addon import its own css-modules based CSS (to get rid of ember-css-modules), so the consuming app could already switch to optimized Embroider (which ember-css-modules does not support) without requiring all addons to migrate to v2.

FWIW, this (v1 addon support of this feature) is not anymore a priority for us, but maybe it's still good to allow this!?

[ef4]

This is a good point.

I want to use this feature to make a package like https://github.com/cardstack/glimmer-scoped-css work in classic builds, and for that story to be complete you'd want a v1 addon to be able to use it too.

[MrChocolatine]

Since you force the type, could this work/be considered:

Suggested change

	let host: AppInstance & {
	trees: {
	app: Node;
	};
	} = _host as any;
	let host = _host as AppInstance & {
	trees: {
	app: Node;
	};
	};