Add "types" to "exports"

[ChocolateLoverRaj]

Pull Request

Problem

Fixes #1703

Solution

Add "types" to "exports"

ChangeLog

[shadowspawn]

Thanks. The example on this page: https://www.typescriptlang.org/docs/handbook/esm-node.html#packagejson-exports-imports-and-self-referencing

has a comment saying "types" must come first:

            // Entry-point for TypeScript resolution - must occur first!
            "types": "./types/index.d.ts",

(It did work for me last when I was experimenting, but I think we better follow the example.)

[shadowspawn]

This PR is to work with a future version of TypeScript. I have been doing a lot of reading to try and understand whether it is safe for us to ship now. And still not sure! Maybe I should ask...

1. The "types" value in "exports" is described in the Node.js 16 documentation so that part at least appears in something released.
   https://nodejs.org/dist/latest-v16.x/docs/api/packages.html#community-conditions-definitions

2. I found these comments in long threads, two talking about updates by library authors:

• Concerns with TypeScript 4.5's Node 12+ ESM Support microsoft/TypeScript#46452 (comment)
• Concerns with TypeScript 4.5's Node 12+ ESM Support microsoft/TypeScript#46452 (comment)
• Surprising (or incorrect) priorities with package.json exports fields? microsoft/TypeScript#46334 (comment)

Some interesting information about emit vs resolving with answer from an expert:

• https://stackoverflow.com/questions/71463698/why-we-need-nodenext-typescript-compiler-option-when-we-have-esnext

3. rxjs have merged a PR doing this just recently, and also wondering whether to go before TypeScript supports it!

• fix(esm): add types to exports ReactiveX/rxjs#6802

[shadowspawn]

Asked if stable enough for release: microsoft/TypeScript#46452 (comment)

[shadowspawn]

And got a "100% yes".

microsoft/TypeScript#46452 (comment)

[shadowspawn]

Oh, but then there was a followup. I need to reread some of the earlier comments again!

microsoft/TypeScript#46452 (comment)

[ChocolateLoverRaj]

@shadowspawn How could adding a "types" entry in "exports" break things?

[shadowspawn]

How could adding a "types" entry in "exports" break things?

In general, by making the behaviour worse for a use case where something reads "exports" and recognises the "types" entry. Not just TypeScript, say ts-node or WebStorm. (Hypothetical examples, I have not idea what they do with "exports"!)

[shadowspawn]

@abetomo I am going to test now one more time with typescript@next generating CommonJS and ESM, then call it good. Could make it into v9.1, but no worries if it misses.

[shadowspawn]

LGTM

[abetomo]

👍

[abetomo]

I think it is fine to release it next time.

[shadowspawn]

Ok. I won't merge until after release we have lined up.