package.json diagnostics in --module nodenext

[andrewbranch]

In #46334, it became clear that it’s very easy to mess up writing export maps that will work correctly with --module nodenext. We would like to explore issuing diagnostics in package.json files in two scenarios (only in node12 and nodenext):

• A types condition is not the first condition in an export map
• A default condition is not the last condition in an export map

VS Code currently doesn’t synchronize unsaved changes to package.json files to TS Server (same as tsconfig.json files), so sending errors to the editor can only be done after a manual save. After getting the diagnostics in tsc, we’ll have to evaluate whether the experience in the editor is acceptable, or if we need to start syncing live changes to TS Server.

[dummdidumm]

If you want types to be the first condition I suggest to update the 4.5 beta blog posts like https://devblogs.microsoft.com/typescript/announcing-typescript-4-5-beta/ which contain the, according to you, wrong order (types is last in the exports map example)

[andrewbranch]

I think we fixed that for the RC/stable post, @DanielRosenwasser is it worth going back to that?

[DanielRosenwasser]

Let's discuss this at an upcoming design meeting.