[heft] [typescript] Emit declarations for all module kinds

[Faithfinder]

> In short, you cannot use a single *.d.ts file to type an ESM and CJS implementation file at the same time. Another way of saying the same thing is that the declaration file extension has to match the extension of what it’s typing—.d.ts=.js, .d.cjs = .cjs, etc...
-- A. Branch

As far as I know this guy is the one who understand the modules mess the best, so I think to correctly create dual packages, you need to emit source maps and types for both module kinds.

[iclanton]

@dmichon-msft - Can you take a look at this?

[dmichon-msft]

Very straightforward request, we simply need a way to specify in the additionalModuleKindsToEmit that emitting declarations for the alternate kind is desired, then have it update the options here:
https://github.com/microsoft/rushstack/blob/main/heft-plugins/heft-typescript-plugin/src/configureProgramForMultiEmit.ts#L84-L86

[Faithfinder]

Relatedly, this combination of settings in typescript.json (with tsconfig set to emit esnext)

    "additionalModuleKindsToEmit": [
        {
            "moduleKind": "commonjs",
            "outFolderName": "lib-commonjs"
        }
    ],
    "emitCjsExtensionForCommonJS": true,

Gives me [build:typescript] Module kind "commonjs" is already emitted at /bla/bla/lib with extension '.cjs' by option emitCjsExtensionForCommonJS..

Correct choices to emit for "dual package" would be:

1. js and cjs for "ESM-first" package
2. mjs and js for "CJS-first" package
3. mjs and cjs for "no ambiguity, just look at file type"

[octogonz]

Do we have a proposal for what the typescript.json config file setting should look like to support this?

[Faithfinder]

I can make a proposal:

To the additionalModuleKindsToEmit config objects, add

• extension: default is .js.
  • Options:
    • Can be an enum of .js, .mjs, .cjs.
    • Can be a free text field, who knows what the crazy people will come up with for extensions.
  • Constraints:
    • Needs to respect x suffix for react.
    • Should leave explicit .mts/.cts alone.
• emitDeclarations:
  • Default:
    • true - that's really the correct behaviour
    • false - will make this change non-breaking
    • auto - Respect original tsconfig.json settings?
  • Options:
    • Could instead expose all the tsconfig related settings individually (declaration, sourceMap, declarationMap and inlineSources, I believe?)
  • Constraints:
    • Should respect the extension field above and produce .d.cts/.d.mts files

P.S. I'd also allow to emit the same module kind multiple times. I don't have a specific purpose in mind, but the [build:typescript] Module kind "commonjs" is already emitted at /bla/bla/lib with extension '.cjs' by option emitCjsExtensionForCommonJS. error was annoying to see. I wanted to shout "Just emit stuff, dammit, I wanna see the result"

[Faithfinder]

Also see https://github.com/arethetypeswrong/arethetypeswrong.github.io/tree/main/docs/problems if you want a dive into the problems this solves =P