[BUG] Description

Description

The generator at:

https://github.com/OpenAPITools/openapi-generator/blob/v6.0.1/modules/openapi-generator/src/main/resources/typescript-angular/apiInterface.mustache

uses a return type of Observable<{}> if returnType is not specified. This conflicts with the Observable<any> return type in the implementation file for the same condition:

https://github.com/OpenAPITools/openapi-generator/blob/v6.0.1/modules/openapi-generator/src/main/resources/typescript-angular/api.service.mustache

I don't know if this causes any direct problems with the code generated as default, but the difference is surely not deliberate.

This does cause a problem when modifying the apiInterface.mustache to generate abstract class instead of interface. Using abstract class makes it possible to implement patterns such as

https://medium.com/javascript-everyday/config-based-service-implementation-in-angular-ff39ac2a7f04

ie, if generated code is something like

abstract class NewServiceInterface
{
  abstract doThing(): Observable<{}>;
}

class NewService implements NewServiceInterface
{

  doThing(): Observable<any>
  {
    return of([42]);
  }
}

then

    const ns : NewServiceInterface = new NewService();
    ns.doThing().subscribe(response => {
      console.log("RE", response, response.map((v:number) => v*2));
    });

gives this error:

error TS2339: Property 'map' does not exist on type '{}'.

34       console.log("RE", response, response.map((v:number) => v*2));
                                              ~~~

Changing the interface line to

abstract doThing(): Observable<any>;

resolves the issue.

Compare the return types in modules/openapi-generator/src/main/resources/typescript-angular/apiInterface.mustache and api.service.mustache when returnType is unspecified. Reproduce the abstract-class example to confirm the type mismatch, then verify that generated TypeScript uses a consistent return type and no longer produces the reported property error.