Can't use node-option with ts-node

[ericvergnaud]

Prerequisites

• Checked that your issue hasn't already been filed by cross-referencing issues with the faq label
• Checked next-gen ES issues and syntax problems by using the same environment and/or transpiler configuration without Mocha to ensure it isn't just a feature that actually isn't supported in the environment in question or a bug in your code.
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Description

when running mocha with both ts-node and node-option parameters, ts-node file extensions (.ts) are no longer supported

Steps to Reproduce

• Create a project with type module, install mocha, typescript, ts-node and ts-loader
• typescript file test.spec.ts
• run node node_modules/mocha/bin/mocha.js --no-warnings --loader=ts-node/esm --require ts-node/register --ui bdd --node-option experimental-wasm-gc src/test.spec.ts

Expected behavior:

I expect the test to run

Actual behavior:

When running the above, I get a TypeError: Unknown file extension ".ts"
If I remove --node-option experimental-wasm-gc I don't get the error
If I run node --experimental-wasm-gc node_modules/mocha/bin/mocha.js --no-warnings --loader=ts-node/esm --require ts-node/register --ui bdd src/test.spec.ts, then the test complains that the experimental-wasm-gc option is missing (I'm loading a WebAssembly)

Reproduces how often:

Always

Versions

• The output of mocha --version:
  10.1.0
• The output of node_modules/.bin/mocha --version:
  10.1.0
• The output of node --version:
  v21.3.0
• Your operating system
  • name and version: MacOS Ventura Version 13.0 (22A380)
  • architecture (32 or 64-bit): 64
• Your shell (e.g., bash, zsh, PowerShell, cmd): bash
• Your browser and version (if running browser tests): n/a
• Any third-party Mocha-related modules (and their versions):
  ts-loader": "^9.4.1
  "ts-node": "^10.9.1",
• Any code transpiler (e.g., TypeScript, CoffeeScript, Babel) being used (and its version):
  tsc Version 4.9.5

Additional Information

[ericvergnaud]

It seems the issue could be located in mocha.js lines 84-86, where the presence of node-option drops the already parsed node args (in nodeArgs variable) instead of combining them

[JoshuaKGoldberg]

Curiosity: why provide both --loader=ts-node/esm and --require=ts-node/register?

The list of steps provided seems reasonable, but I'm not getting the exact same output locally. Could you please post an isolated reproduction that a maintainer can run with only 1-2 commands, such as a GitHub repository, GitHub Gist, or Stackbliz container?

[ericvergnaud]

you need ts-node/register to compile ts on the fly
you need ts-node/esm to use esm module syntax

Here is an example
MochaBug.zip

[JoshuaKGoldberg]

Got it, thanks! Makes sense. +1 to your (very helpful, thanks!) comment that Mocha is overriding the implicit-ish --loader=ts-node Node option with the explicit --node-option experimental-wasm-gc. If you pass in --node-option loader=ts-node/esm instead, then everything works happily.

$ node node_modules/mocha/bin/mocha.js --no-warnings --require ts-node/register --ui bdd --node-option loader=ts-node/esm --node-option experimental-wasm-gc src/test.spec.ts                     
(node:37672) ExperimentalWarning: `--experimental-loader` may be removed in the future; instead use `register()`:
--import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register("ts-node/esm", pathToFileURL("./"));'
(Use `node --trace-warnings ...` to show where the warning was created)


Hi there!
  ✔ runs a test

  1 passing (1ms)

...where "happily" ignores the loader notice. That's discussed in #5002.

I think we can consider this a docs issue similar to #5002 that it's not clear how to use Node import/loader/require options together. Filed #5087 to track adding docs. It links to mochajs/mocha-examples#76 as a start.

Aside: in general, it's not great practice to upload a .zip. Downloading and extracting arbitrary files from the internet is kind of scary for us maintainers 🫠. An isolated GitHub repository, Gist, Stackblitz, or other more transparent environment would be nice in the future. This zip works for now.

Thanks for filing!