fix: import yargs/yargs in esm projects

[hongaar]

When using import yargs from "yargs/yargs" in an ESM project ("type": "module" in package.json), Node.js will throw this error:

internal/process/esm_loader.js:74
    internalBinding('errors').triggerUncaughtException(
                              ^

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension "" for /home/runner/work/bandersnatch/bandersnatch/tests/smoke/esm/node_modules/yargs/yargs
    at new NodeError (internal/errors.js:322:7)
    at Loader.defaultGetFormat [as _getFormat] (internal/modules/esm/get_format.js:71:15)
    at Loader.getFormat (internal/modules/esm/loader.js:105:[42](https://github.com/hongaar/bandersnatch/runs/5661229728?check_suite_focus=true#step:8:42))
    at Loader.getModuleJob (internal/modules/esm/loader.js:2[43](https://github.com/hongaar/bandersnatch/runs/5661229728?check_suite_focus=true#step:8:43):31)
    at async ModuleWrap.<anonymous> (internal/modules/esm/module_job.js:78:21)
    at async Promise.all (index 3)
    at async link (internal/modules/esm/module_job.js:83:9) {
  code: 'ERR_UNKNOWN_FILE_EXTENSION'

To solve this, add a new yargs.mjs file and update the ./yargs export in the package.json.

Confirmed that this works for a simple ESM project where yargs is a transitive dependency: hongaar/bandersnatch#392 (in tests/smoke/esm)

Related to #2014

[bcoe]

@hongaar what Node.js versions does this problem arise in? It sounded like this was an error that begins happening in v17, according to #2014.

I believe the yargs.mjs file caused issues on some Node versions, which is how I landed on an yargs with no extension.

[hongaar]

This is already happening with Node.js >= 12 as far as I can see.

The bandersnatch CI fails with this error for all common versions of Node.js (https://github.com/hongaar/bandersnatch/actions/runs/2029079244)

The failing test is running a ESM project with this package.json:

{
    "name": "bandersnatch-smoke-test-esm",
    "type": "module",
    "scripts": {
        "test": "node index.mjs"
    },
    "dependencies": {
        "bandersnatch": "^1.9.2"
    }
}

yargs is loaded through the bandersnatch dependency with:

import createYargs from 'yargs/yargs';

[hongaar]

@bcoe Is there anything I can do to help this get merged? I could add a simple smoke test (like in the bandersnatch project) to confirm this change is working as intended?

[bcoe]

@hongaar thank you for the patch, hopefully it does the trick for you.

[hongaar]

@bcoe thanks for merging this! I forgot to add the new file to the package.json list array and opened a new PR here to fix this: #2185