no-explicit-generics doesn't work correctly

[mark-akturatech]

version: 0.6.0

Gday,
First - great job. Thank you.

Not sure if worth removing no-explicit-generics from strict rule set.

The rule is generating an error for lines of code like this...

private readonly itemSelectionUpdateSubject$ = new BehaviorSubject<ItemSelectionModel | undefined>(undefined);

If i follow the rule and remove the generic then when the subject is set it will error as the subject has type 'undefined'.

Maybe an option to ignore undefined could work here or probably would be better if the rule ignored generics with union types (or had an option to enable that behavior).

[Dmytro27Ind]

I encountered a similar issue where ESLint reports the following error:
ESLint: Explicit generic type arguments are forbidden.(rxjs-x/ no-explicit-generics)

Here's the original code that triggered the error:

private itemsLoadedSubject$ = new BehaviorSubject<ListItem | null>(null);

However, I couldn't remove the explicit ListItem type because, without it, the inferred type defaults to null.

To resolve this, I updated the code as follows:

private itemsLoadedSubject$ = new BehaviorSubject<ListItem | null>(null); // eslint-disable-line rxjs-x/no-explicit-generics

(version 0.6.0)

[Dmytro27Ind]

Proposed Solution

Introduce a configuration option for the rule to allow explicit generics specifically for union types. For example:

"rxjs-x/no-explicit-generics": [ "error", { "allowUnionTypes": true } ]

[JasonWeinzierl]

It looks like this is a known issue in the upstream repos:

• "rxjs-no-explicit-generics" warns against "new BehaviorSubject<string[]>([])" cartant/rxjs-tslint-rules#95
• [no-explicit-generics] False positive when the generic isn't *exactly* the infered type cartant/eslint-plugin-rxjs#102

typescript-eslint itself may add support for this in the future: typescript-eslint/typescript-eslint#4978 . If that issue gets resolved, we may be able remove no-explicit-generics entirely.

But for the time being, I agree this should be removed from the strict configuration until this bug is resolved. I'll be releasing v0.6.1 shortly with this rule removed from strict.

Edit: v0.6.1 is released.

[rdamazio]

Thanks for all the work on this plugin btw!

Is it sufficient to check if the generic type exactly matches the default value type? (so e.g. a union type wouldn't exactly match, and thus it wouldn't warn then)

[JasonWeinzierl]

This is fixed in v0.7.4

[rdamazio]

I updated to v0.7.4 and unfortunately am still seeing a false trigger if I enable this rule, specifically on this line:

https://github.com/rdamazio/efis-editor/blob/1352d61ea19153c55deb6064c6c2428d0d336d67/src/app/shared/gdrive/gdrive.component.spec.ts#L32

What I see:

/Users/rdamazio/Development/efis-editor/src/app/shared/gdrive/gdrive.component.spec.ts
  32:18  error  Explicit generic type arguments are forbidden  rxjs-x/no-explicit-generics

and if I remove the generic, I get:

Error: src/app/shared/gdrive/gdrive.component.spec.ts:32:5 - error TS2322: Type 'BehaviorSubject<DriveSyncState.DISCONNECTED>' is not assignable to type 'BehaviorSubject<DriveSyncState>'.
  Types of property 'observers' are incompatible.
    Type 'Observer<DriveSyncState.DISCONNECTED>[]' is not assignable to type 'Observer<DriveSyncState>[]'.
      Type 'Observer<DriveSyncState.DISCONNECTED>' is not assignable to type 'Observer<DriveSyncState>'.
        Type 'DriveSyncState' is not assignable to type 'DriveSyncState.DISCONNECTED'.

32     state$ = new BehaviorSubject(DriveSyncState.DISCONNECTED);
       ~~~~~~

Output from ng version:

Angular CLI: 19.2.13
Node: 23.9.0 (Unsupported)
Package Manager: npm 11.4.0
OS: darwin x64

Angular: 19.2.13
... animations, cli, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, platform-server
... router, service-worker, ssr

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1902.13
@angular-devkit/build-angular   19.2.13
@angular-devkit/core            19.2.13
@angular-devkit/schematics      19.2.13
@angular/cdk                    19.2.17
@angular/material               19.2.17
@schematics/angular             19.2.13
rxjs                            7.8.2
typescript                      5.8.3
zone.js                         0.15.1

Let me know if I should file a separate bug instead, but the underlying issue here is pretty much the same.

[JasonWeinzierl]

Ah I see. The fix released for v0.7.4 only addressed union types declared inline in the subject's generic type... not union types or enums declared elsewhere. Reopening. Sorry for the false hope!