NSwag: Tons of errors after upgrading to the latest version of Nswag Studio

I don’t think this was properly fixed, since the errors I get with version 13.12.1.0 are very similar. Upgrading and simply generating the Angular TypeScript files now changes return _observableOf<T>(<any>null); to return _observableOf(null); for a method that has a return type of Observable<T>. This generates the following error:

error TS2322: Type 'Observable<null>' is not assignable to type 'Observable<T>'.

Note that this error should only occur when strictNullChecks is set to true for the TypeScript compiler. This sets null and undefined as separate types instead of adding it implicitly to every type.

For it to work with that strict flag enabled, the return type should be Observable<T | null>.

Type errors aside, I also don’t think the behavior is entirely correct. If you take the process method (see below) the return _observableOf(null) statement is actually undefined behavior and should not return a null value, but rather throw an error. When any status code is encoutered that was not defined, it should go through return throwException(...) I feel. There might be some extra code to handle the 204 response (which was not defined, so I don’t think it belongs here since we are also now adding | null to the contract which isn’t necessarily the case), but the last else if statement should just be an else statement so the last return statement can be removed.

Original code

protected processCall(response: HttpResponseBase): Observable<string[]> {
    const status = response.status;
    const responseBlob =
        response instanceof HttpResponse ? response.body :
        (<any>response).error instanceof Blob ? (<any>response).error : undefined;

    let _headers: any = {}; if (response.headers) { for (let key of response.headers.keys()) { _headers[key] = response.headers.get(key); }}
    if (status === 200) {
        return blobToText(responseBlob).pipe(_observableMergeMap(_responseText => {
        let result200: any = null;
        result200 = _responseText === "" ? null : <string[]>JSON.parse(_responseText, this.jsonParseReviver);
        return _observableOf(result200);
        }));
    } else if (status !== 200 && status !== 204) {
        return blobToText(responseBlob).pipe(_observableMergeMap(_responseText => {
        return throwException("An unexpected server error occurred.", status, _responseText, _headers);
        }));
    }
    return _observableOf(null);
}

Proposed code

protected processCall(response: HttpResponseBase): Observable<string[]> {
    const status = response.status;
    const responseBlob =
        response instanceof HttpResponse ? response.body :
        (<any>response).error instanceof Blob ? (<any>response).error : undefined;

    let _headers: any = {}; if (response.headers) { for (let key of response.headers.keys()) { _headers[key] = response.headers.get(key); }}
    if (status === 200) {
        return blobToText(responseBlob).pipe(_observableMergeMap(_responseText => {
            let result200: any = null;
            result200 = _responseText === "" ? null : <string[]>JSON.parse(_responseText, this.jsonParseReviver);
            return _observableOf(result200);
        }));
    } else { // Removed special 204 handling since it was never defined in the first place
        return blobToText(responseBlob).pipe(_observableMergeMap(_responseText => {
            return throwException("An unexpected server error occurred.", status, _responseText, _headers);
        }));
    }
    // We can now safely remove the return _observableOf(null) since the method can never arrive here
}

Fixed in v13.12.1

I’m not sure if the project qualifies for a “bigger project”, it’s got around 15k lines in the generated client after formatting with Prettier.

I’ve just tested it, and everything seems to work for me.

See https://github.com/RicoSuter/NSwag/issues/3566

For your question about downgrading, you can find all the versions in the github releases of this repo.