Weird import / bundling issue when using date-fns

[vladjerca]

If I import a specific method from date-fns the module is incorrectly resolved.

eg:

import addDays from 'date-fns/addDays'

File.ts:

import addDays from 'date-fns/addDays';

export function useDateFns() {
    console.log(addDays(new Date(), 10));
}

File.spec.ts:

import { useDateFns } from './File';

fdescribe('File', () => {
    it('should return void', () => {
        expect(useDateFns()).toBeUndefined();
    });
});

The test fails with the following error:

SourceMap position not found for trace: TypeError: addDays_1.default is not a function

Here comes the juicy part, running the test with the debugger attached renders this:

This does not hold up when running the application in production, it can only be reproduced via karma-typescript 😱

Basically from what I can tell is that the bundler is somehow loading the entire date-fns library instead of targeting date-fns/addDays specifically.

LE:

karma-typescript: 5.1.0 (latest as of when this issue was opened)

The only workaround I've found for this ATM is to do a really gross hack in my test configuration script

import * as dateFns from 'date-fns';
import addDays from 'date-fns/addDays';

(addDays as any) = dateFns.addDays;

Let me know if there's any more information I can provide 👍

[vladjerca]

@erikbarke

If this helps, I've managed to find the source of the issue.

Within the Resolver.ts:166 at this point the moduleName is overwritten from date-fns/addDays to date-fns.

The cause of this issue is that the regex ends up getting applied on .../node_modules/date-fns/typings.d.ts for some reason.

LE: The real question is why is the filename resolving the typings, this may be potentially normal behavior, sadly I lack a proper understanding of the source to determine it at this point 😬

[erikbarke]

Are you using compiler paths?

[vladjerca]

@erikbarke No, this happens with out of the box configuration.

LE: if you want I can create a simple repro repository.

[vladjerca]

@erikbarke Here's a repo that should reproduce the issue: https://github.com/vladjerca/karma-typescript-import-bug