Flow: module.name_mapper does not find nested modules on windows

Created on 21 Sep 2018 · 7Comments · Source: facebook/flow

I'm having a folder structure:

modules/Test/js/main.js
modules/Test/js/nested/entry.js

a root test.js file:

/* @flow */

import main from '#Test/main';
import main2 from '#Test/nested/entry';

a name mapper:
module.name_mapper='^#$.+?$/$.*$$'->'<PROJECT_ROOT>/modules/\1/js/\2'

and it constantly throws Cannot resolve module #Test/nested/entry. Tried a bunch of other variants and nothing resolves the nested file. It finds #Test/main without any problems, but once it's a nested path, it does not recognize it.

This regex works fine with webpack and jest, e.g. jest:

"moduleNameMapper": {
  "^#(.+?)/(.*)$": "<rootDir>/modules/$1/js/$2"
}

v0.81.0

bug

Source

donnysim

Most helpful comment

Spent a while looking into this one and it turns out the \\ / Windows usage is a red herring. The root issue is that, unlike Webpack and Jest, OCaml regexp doesn't support non-greedy capture groups (.+?) - reference.

This example works if you change your name mapper to something like:

module.name_mapper='^#\([^/]+\)/\(.*\)$'->'<PROJECT_ROOT>/modules/\1/js/\2'

...otherwise it is rewriting your nested module name incorrectly, to modules\Test\nested\js\entry.js (nested and js wrong way round as the first capture group is greedy).

jamesisaac on 2 Mar 2019

👍3

All 7 comments

Seems like a windows problem? it does resolve #Test/nested\\entry without any problems so I'm guessing it's folder separator problem. Any ways to overcome this?

donnysim on 21 Sep 2018

This example works if you change your name mapper to something like:

module.name_mapper='^#\([^/]+\)/\(.*\)$'->'<PROJECT_ROOT>/modules/\1/js/\2'

...otherwise it is rewriting your nested module name incorrectly, to modules\Test\nested\js\entry.js (nested and js wrong way round as the first capture group is greedy).

jamesisaac on 2 Mar 2019

👍3

cc @avikchaudhuri

jamesisaac on 2 Mar 2019

Closing as the Flow team don't have plans to move away from OCaml regex.

jamesisaac on 7 Mar 2019

Sorry I missed notifications on this issue, @jamesisaac. I believe the Flow team is open to more JS-friendly configuration, and we've had some recent internal threads on this topic. I can't give a timeline but I'm optimistic that we will do something to avoid issues like this one.

avikchaudhuri on 7 Mar 2019

❤1 👍1

Nice! I was just relaying what I heard on Discord the other week, but that sounds cool if you guys have plans around improved compatibility with the JS ecosystem.

While this issue's a good example of the confusion it can cause, I guess that's better tracked in something like #153 ? I'll make a note there.

jamesisaac on 8 Mar 2019

I believe the Flow team is open to more JS-friendly configuration, and we've had some recent internal threads on this topic. I can't give a timeline but I'm optimistic that we will do something to avoid issues like this one.

For reference/easier findability, these are the flowconfig related issues/suggestions I found that would bring it in line with other tools like eslint, babel, webpack, etc: