baseUrl has a side effect on the used dependency export

Is

If I use ts-node together with tsconfig-paths/register and a tsconfig baseUrl of ./node_modules the runtime seems to “ignore” package.json exports of dependencies and uses the wrong file. As the bottom example shows it uses colorette/index.js but it should use colorette/index.cjs.

Should

It should use the correct dependency dist as defined by its package.json exports, so for colorette it should use colorette/index.cjs.

Reproduction

• tsconfig-paths-exports-repro-master.zip
• npm install && npm start

Trace

Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: xyz/node_modules/colorette/index.js
require() of ES modules is not supported.
require() of xyz/node_modules/colorette/index.js from xyz/node_modules/autoprefixer/lib/autoprefixer.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which defines all .js files in that package scope as ES modules.
Instead rename index.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from xyz/node_modules/colorette/package.json.

    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1217:13)
    at Module.load (internal/modules/cjs/loader.js:1050:32)
    at Function.Module._load (internal/modules/cjs/loader.js:938:14)
    at Module.require (internal/modules/cjs/loader.js:1090:19)
    at require (internal/modules/cjs/helpers.js:75:18)
    at Object.<anonymous> (xyz/node_modules/autoprefixer/lib/autoprefixer.js:5:17)
    at Module._compile (internal/modules/cjs/loader.js:1201:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1221:10)
    at Module.load (internal/modules/cjs/loader.js:1050:32)
    at Function.Module._load (internal/modules/cjs/loader.js:938:14)

Background:

• At first I thought this is related to TypeStrong/ts-node#935 / TypeStrong/ts-node#1007 but after working out a reproduction case I figured out that the error only happens with tsconfig-paths and the mentioned baseUrl value 🙈.
• The reason why I used a baseUrl of “./node_modules” in the first place was because my root folder has some folders with the same name as some dependencies, a baseUrl of “.” resulted in typescript importing my /xyz instead of /node_modules/xyz 😉.

[jonaskello]

@katywings It is already covered by this test:

https://github.com/dividab/tsconfig-paths/blob/2461cc9c0aa6f02f27c679d1344adaf35ff05cf7/test/data/match-path-data.ts#L128-L142

[jonaskello]

I did an experiment/repro here that does not involve ts-node or any bundling. It just uses tsc and node. It works without tsconfig-paths loaded but not with it.

Looking into colorette I found it has "type": "module" set in package.json. That means that every .js file should be treated as a ESM module. So the index.js file is in ESM format. To be backwards compatible with the old node resolution it also has "main": "index.cjs". Since older versions of node only check the main field they will require index.cjs and it works. This means tsconfig-paths should also require this file but somehow it seems to require index.js instead. I think this is a bug since if there is an explicit file extension for the file in the main field it should be used as-is. (Note that the module field is not used at all by node as far as I know, it is only webapck that checks that field.)