Use the dedicated PostCSS API for errors

[binyamin]

PostCSS has a dedicated API method for errors. This codebase is inconsistent. It only uses it in lib/assign-layer-names.js.

For example:

postcss-import/lib/resolve-id.js

Lines 35 to 39 in b7d1939

	throw new Error(
	`Failed to find '${id}'
	in [
	${paths.join(",\n ")}
	]`

Also:

postcss-import/index.js

Lines 261 to 265 in b7d1939

	throw new Error(
	`Incompatable @charset statements:
	${stmt.node.params} specified in ${stmt.node.source.input.file}
	${charset.node.params} specified in ${charset.node.source.input.file}`
	)

[binyamin]

Also, may I rewrite the code using ESM? Or at least using async functions, instead of using Promise? It might be easier to read.

[RyanZim]

Good call on the error API; PR welcome.

As for async: I agree it would be an improvement; I just never got the time to devote to a full codebase refactor. I'm also unsure how good our test coverage is at the moment, we should probably get some coverage measurement in first and make sure that's in tip-top shape before attempting an async refactor. If you want to take it on, more power to you!

I'm unsure if I want to migrate to ESM right away; since ESM modules cannot be imported in CJS. Support for postcss.config.mjs landed less than a year ago, there's probably quite a few people still using it; I don't want to cause unnecessary ecosystem churn. In any case, that would be best done as a separate refactor, after async.