tsconfig.json/paths not working with ts-node

[unional]

One neat trick to use tsconfig.json/paths is to pointing the module name to your source file:

// tsconfig.json of blue-tape-fixture
{
  ...
  "paths": {
    "blue-tape-fixture": [ "src/" ]
  }
}

This way, your test files can reference the source as if it is a proper module:

You can see it is working in vscode. But it does not when I run test with ts-node:

// package.json
{
  "scripts": {
    "test": "ts-node -P tsconfig.build.json node_modules/blue-tape/bin/blue-tape \"test/**/*.ts\" | tap-spec"
  }
}

The error is:

Error: Cannot find module 'blue-tape-fixture'
    at Function.Module._resolveFilename (module.js:325:15)
    at Function.Module._load (module.js:276:25)
    at Module.require (module.js:353:17)

You can see it here: https://github.com/unional/blue-tape-fixture/tree/ts-node

# clone
npm install
npm test

[blakeembrey]

@unional That's the node.js error - TypeScript is working fine, but node will never be able to resolve an alias like that unless TypeScript emits code that rewrites paths. What do you think is the solution here?

[unional]

I see. In order for it to work, a module-path-rewriter need to be written and loaded by ts-node.
Alternatively is to load the transpiled code dist/*, which kind of defeat the purpose of ts-node (I said kind of because the test files, in this use case, can remain as ts files).

[blakeembrey]

This module uses the emitted code though - it's TypeScript itself that doesn't do any rewriting right?

[unional]

Just check. Nope it does not do any rewriting. Seems like the baseUrl and paths is only used during compilation. By design or bug on TS side?

[unional]

Updated https://github.com/unional/blue-tape-fixture/tree/ts-node to demo the issue.
run npm run build-test and see under dist/test/index.ts. It is still requiring blue-tape-fixture

[unional]

Confirm above statement: microsoft/TypeScript#5039 (comment)

[blakeembrey]

@unional Yeah, it's tricky. I can understand TypeScript's stance, if they don't have a solution for it built-in I think we can investigate adding a plugin once they implement the pluggable transforms in TypeScript 2.0. This is definitely more of a user-land feature.

[sanex3339]

any news? i want to use 'paths' option in my tests

[blakeembrey]

No, it does not work and is not expected to work. Someone can still implement a plugin (which would be very valuable to others too!), but I am not currently working on it.

[jonaskello]

Maybe this could be solved by augmenting node's loading rather than having typescript re-write the paths. There are some alternatives mentioned here. In particular I'm thinking that wrapping the global require and just changing the path according to tsconfig would be the simplest solution.

[jonaskello]

When I looked closer I realised that wrapping global require is not possible in a way that replaces it (the example above installs a separate require function). However it is possible to patch Module._load like is done in mock-require. I did some experiments with this and it seems doable. I'll try to put together a PR to demonstrate.

[jonaskello]

For those interested I did a PR to enable execution of projects with tsconfig paths in #254.