Support tsconfig paths mapping similar to Jest's moduleNameMapper

[ackvf]

Is your feature request related to a problem or a nice-to-have?? Please describe.

In a TypeScript project that uses custom paths aliases in tsconfig.json, it is not possible to import files using e.g. @abi/something, which is mapped in tsconfig.json like this

    "paths": {
      "@abi/*": ["abi/*"]
    }

Describe the solution you'd like
The custom paths are supported by jest using modulenamemapper

https://jestjs.io/docs/configuration#modulenamemapper-objectstring-string--arraystring

Describe alternatives you've considered
using hardhat plugins

[ackvf]

see https://www.npmjs.com/package/tsconfig-paths

[ackvf]

So, I actually think that the issue was caused not by the @abi path alias, but by the fact that I was importing a json file directly, which works in the project thanks to tsconfig resolveJsonModule: true, but it doesn't seem to work in mocha tests.

[ackvf]

Well, this is weird, I don't really understand what is going on.

this doesn't work

import AABI from '@abi/ExampleABI.json'

this works

import AABI from '../abi/ExampleABI.json'

However, this also seems to be working, although it might be that it is just a type.

import type { ExampleABI } from '@typings/abi'

What is going on? How can I use imports with path aliases and json files?

[JoshuaKGoldberg]

Sounds like this is a question more than anything else. Closing as questions should go in Discord or StackOverflow. Good luck!

[ackvf]

So, path aliases are supported by mocha, am I reading this right?

Because in my previous experiment, it was clear that

this doesn't work

import AABI from '@abi/ExampleABI.json'

and this works

import AABI from '../abi/ExampleABI.json'

[JoshuaKGoldberg]

(re-opening to put back in the triage queue)

[JoshuaKGoldberg]

Ok, yes, coming back to this now that I know more about Mocha: you're correct that Mocha doesn't natively support path aliases. Mocha directly runs JavaScript files. It doesn't set up fancy virtual environments with mapped names the way, say, Jest's moduleNameMapper does.

Mocha does support using Node.js-style loaders that can modify files on the fly - including rewriting import paths and/or transpiling TypeScript syntax to pure JavaScript. mochajs/mocha-examples#75 -> mochajs/mocha-examples#76 shows a couple examples of that.

If that examples repo & its open PRs doesn't include an example of using Mocha+TypeScript the way you're looking for, I'd suggest filing an issue on the repo. There's definitely a lot missing at the moment. Cheers! 🤎