--experimental-loader does not work

[rickyes]

Use --experimental-loader in the test file to launch the subprocess.

• Nodejs Version: v14.2.0
• Tap Version: v14.10.7

// coffee.test.js
const { test } = require('tap');
const path = require('path');
const { spawnSync } = require('child_process');

const PATH_ESM_LOADER = path.join(__dirname, 'coffeescript-loader.mjs');
const PATH_MAIN = path.join(__dirname, 'main.coffee');

test('test esm', t => {
  spawnSync(process.execPath, [
    '--experimental-loader',
    PATH_ESM_LOADER,
    PATH_MAIN
  ], { encoding: 'utf8', stdio: 'inherit' });
  t.end();
});

1. Running with tap causes errors:

$ tap coffee.test.js

coffee.test.js 2> internal/modules/run_main.js:54
coffee.test.js 2>     internalBinding('errors').triggerUncaughtException(
coffee.test.js 2>                               ^
coffee.test.js 2>
coffee.test.js 2> TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension "" for /Users/ricky/.node-spawn-wrap-92169-8c7dd84acf79/node
esm/coffee.test.js 2>     at Loader.defaultGetFormat [as _getFormat] (internal/modules/esm/get_format.js:65:15)
coffee.test.js 2>     at Loader.getFormat (internal/modules/esm/loader.js:113:42)
coffee.test.js 2>     at Loader.getModuleJob (internal/modules/esm/loader.js:244:31)
coffee.test.js 2>     at processTicksAndRejections (internal/process/task_queues.js:97:5)
coffee.test.js 2>     at async Loader.import (internal/modules/esm/loader.js:178:17)
coffee.test.js 2>     at async internal/process/esm_loader.js:55:9 {
coffee.test.js 2>   code: 'ERR_UNKNOWN_FILE_EXTENSION'

2. Run successfully with node:

$ node coffee.test.js | tap-mocha-reporter spec

test esm
  ✓ test esm (179.536ms)

  1 passing (192.018ms)

[coreyfarrell]

The issue is a conflict between nyc 14 and current versions of node.js. See nodejs/node#33226 for more information about the error you are seeing. The work-around for tap v14 is to run tap --no-cov coffee.test.js - this disables collection of code coverage. If you need coverage you can install nyc@15 as a development dependency to your own package and run nyc tap --no-cov. Also note coverage of native ES modules is difficult. It only experimentally supported by using @istanbuljs/esm-loader-hook, this would conflict with your own loader hook so I cannot suggest a solution.

Note that tap v15 will use nyc v15 which resolves this issue but this fix is semver-major so it will not be available for tap.

[rickyes]

Thank you for your comments and I will take your comments into account to fix the test case.

[isaacs]

Completely different way of doing this in tap 18. A coffeescript plugin would be easy to write, you can look at the typescript plugin as an example.