Symbol in the module exports array causes fatal error

[andrew-yustyk]

I'm submitting a...

[ ] Regression 
[x] Bug report
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

Currently it isn't possible to use symbol in the exports array.
An example:

// sentry.constants.ts
export const SENTRY_SDK_TOKEN = Symbol('SENTRY_SDK_TOKEN');

// sentry.module.ts
@Module({
  imports: [ConfigModule],
  providers: [
    {
      provide: SENTRY_SDK_TOKEN,
      useFactory: SentryProvider.fromConfigService,
      inject: [ConfigService]
    }
  ],
  exports: [SENTRY_SDK_TOKEN]
})
export class SentryModule {
}

The bug is not reproduced if you use the string instead of the symbol.

Seems like this is a bug in the addExportedComponent() method in the injector module (link).

Current implementation of this method doesn't have a checking of the symbol token, just for the string token.

Expected behavior

Symbol token can be used in the exports section as well as the string token

Environment

Nest version: 5.4.0

For Tooling issues:
- Node version: 10.11.0
- Platform:  Linux

[marcus-sa]

Nest doesn't support using Symbol as a token yet.
You need to use the good ol' strings.
It's already in the roadmap :)

[andrew-yustyk]

Nest supports symbols from 5.3.12
Support was added in Issue #1177

[andrew-yustyk]

There is just a bug or missed functionality. I'll try to create PR for for this issue asap

[marcus-sa]

Oh, my bad then

[andrew-yustyk]

there is need just to update addExportedComponent() method in in the injector module

[marcus-sa]

Anyhow, you should use Symbol.for and not Symbol

[andrew-yustyk]

I think this is depends on your project.
I prefer to use Symbol('some_str') instead of Symbol.for('some_str').
Symbol.for allows other developers do not import the constant with symbol and just use Symbol.for in different places of project. And then an additional time will be spent during refactoring.

In a case of Symbol other developers must import the constant with this symbol.

[marcus-sa]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol

There's a big difference.
You need to use Symbol.for, because EVERY instantiated symbol using Symbol will be unique, so it's impossible to assert it.

Symbol.for('foo') === Symbol.for('foo'); // true
Symbol('foo') === Symbol('foo'); // false

This is exactly the same behavior with InjectionToken in Angular.
That's just an instantiated class with a description, so if you'd create two InjectionToken with the same description, it'd still assert as they're the same, which is exactly the whole point, lol.
You use a prefix when building a library, to make sure no one will create an identical token.

[kamilmysliwiec]

Thanks for reporting!

[kamilmysliwiec]

Published as 5.4.1

[lock]

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