Running jest with ES Modules on windows fails

[jonerer]

🐛 Bug Report

I can't run jest with a project using ES Modules on windows

To Reproduce

Steps to reproduce the behavior:

1. mkdir jestgrej
2. cd jestgrej
3. yarn add --dev yest
4. jest --init
   √ Would you like to use Jest when running "test" script in "package.json"? ... yes
   √ Choose the test environment that will be used for testing » node
   √ Do you want Jest to add coverage reports? ... no
   √ Automatically clear mock calls and instances between every test? ... no
5. jest

C:\prog\node\jestgrej>jest
(node:9068) ExperimentalWarning: The ESM module loader is experimental.
Error [ERR_UNSUPPORTED_ESM_URL_SCHEME]: Only file and data URLs are supported by the default ESM loader
    at Loader.defaultResolve [as _resolve] (internal/modules/esm/resolve.js:33:11)
    at Loader.resolve (internal/modules/esm/loader.js:85:40)
    at Loader.getModuleJob (internal/modules/esm/loader.js:188:40)
    at Loader.import (internal/modules/esm/loader.js:163:28)
    at importModuleDynamically (internal/modules/cjs/loader.js:1094:27)
    at exports.importModuleDynamicallyCallback (internal/process/esm_loader.js:37:14)
    at _default (C:\prog\node\jestgrej\node_modules\jest-config\build\importMjs.js:16:29)
    at readConfigFileAndSetRootDir (C:\prog\node\jestgrej\node_modules\jest-config\build\readConfigFileAndSetRootDir.js:105:61)
    at readConfig (C:\prog\node\jestgrej\node_modules\jest-config\build\index.js:217:65)
    at readConfigs (C:\prog\node\jestgrej\node_modules\jest-config\build\index.js:401:32)

C:\prog\node\jestgrej>

I tried to do some debugging and found the cause. With a breakpoint in node_modules\jest-config\build\importMjs.js:16:29 we can see that this line is run:

var _default = specifier => import(specifier);

With a "specifier" value of C:\prog\node\jestgrej\jest.config.mjs. Doing imports of ES Modules with absolute paths doesn't work on windows. See this other issue I made: nodejs/node#31710

A workaround would be to use relative imports. ./jest.config.mjs would work in this case.

Expected behavior

It should be able to start up and run some tests

envinfo

C:\prog\node\jestgrej>npx envinfo --preset jest
npx: installed 1 in 4.218s

  System:
    OS: Windows 10 10.0.17763
    CPU: (8) x64 Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz
  Binaries:
    Node: 13.8.0 - C:\tools\nodejs\node.EXE
    Yarn: 1.6.0 - C:\Users\jon\AppData\Roaming\npm\yarn.CMD
    npm: 6.4.0 - C:\tools\nodejs\npm.CMD
  npmPackages:
    jest: ^25.1.0 => 25.1.0

I guess this is related to #9430 . But I didn't see any mention of windows there.

[SimenB]

Oh, interesting! We run this on windows CI, odd it didn't pick it up... Does it work if you pass the full path through require('url').pathToFileURL(specifier).href?

[jonerer]

Unsure. Could be. On the node issue they replied that I need to put "file:///" at the start. Is that what your code does? (cant test at the moment)

[SimenB]

Yup, but I'm not sure if that function works without there being a file:// at the start already

[jonerer]

Great, thanks @SimenB !

[SimenB]

Thanks for reporting 👍

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