Replace --entry-type with --input-type, plus --input-type=auto

[GeoffreyBooth]

#66 plus the addition of --input-type=auto. Same logic as #55: if the input string contains an import or export statement, treat it as ESM; otherwise as CommonJS. This is perhaps even more useful for --eval and --print.

I’m submitting this as a separate PR in case people are okay with #66 but uncomfortable with this addition. You can see the difference between the PRs here:

https://github.com/nodejs/ecmascript-modules/compare/flag-for-string-input-only…flag-for-string-input-only-with-auto

It’s the same code as from #55, without -a.

[ljharb]

Repeating my review from #55; If we can’t detect the type unambiguously from syntax, it should throw.

[GeoffreyBooth]

Repeating my review from #55; If we can’t detect the type unambiguously from syntax, it should throw.

I’m not sure what this means. What are you proposing?

The definition of auto is in the docs in this PR: run as ESM if an import or export statement is detected, else run as CommonJS.

That’s perhaps not the holy grail of unambiguous syntax detection, but as we’ve discussed, unambiguous is impossible. Rather than try to come close and fail some of the time, this redefines the goal: import/export = ESM, else CommonJS. The user simply needs to know that that’s what “auto” means. That can be explained in a sentence, and isn’t all that complicated, so I think users can be trusted with this.

[GeoffreyBooth]

Per 2019-04-10 meeting, I’ll refactor this into a separate PR that creates a new function on module, e.g. import { detectImportOrExportStatement } from 'module' or whatever it ends up being named. Then Node is providing this as an API for tools like babel and coffee to have a common, Node-supported way of picking a type to use for unknown JavaScript string input. The tools could use the result of that call in deciding whether to use vm.runScript or vm.runModule or whatever the recommended method is for them to run JavaScript code.

Once that’s done and merged in, we can discuss extending its use to other locations such as --input-type=auto.

[ljharb]

(Let's make sure the API is usable from CJS as well 😄 )

[GeoffreyBooth]

Closing in favor of #69