Can't define a concurrency with a 0 value using the @Processor decorator

[nlenepveu]

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

In the current design of Bull, the concurrency is managed at the processor level and does not allow to easily configure a single queue with no concurrency used by multiple named processors.
Given the fact that concurrency of each processor stacks up for the queue, a workaround exists and consists of defining a concurrency to 0 to every processor of the queue expected the first one. The workaround is described here: OptimalBits/bull#1113.

Using the NestJS/Bull decorator, the code below should do the trick

@Process({ name: NAMED_JOB_1, concurrency: 1 })
async updateJob1(job: Job<any>) { }

@Process({ name: NAMED_JOB_2, concurrency: 0 })
async updateJob2(job: Job<any>) { }

However, any argument with a falsy value is rejected before calling queue.process with the options of the decorator (https://github.com/nestjs/bull/blob/master/lib/bull.explorer.ts#L82).

  handleProcessor(
    instance: object,
    key: string,
    queue: Queue,
    options?: ProcessOptions,
  ) {
    let args = [
      options && options.name,
      options && options.concurrency,
      instance[key].bind(instance) as ProcessCallbackFunction<unknown>,
    ];
    args = args.filter(item => item);
    queue.process.call(queue, ...args);
  }

Expected behavior

Concurrency options with a 0 value should be a valid option and should not be rejected by the @Processor decorator.

    args = args.filter(item => item);

could be changed to

    args = args.filter(item => item !== undefined);

Environment

Nest version: 6.10.14
Nest bull version: 0.0.1
 
For Tooling issues:
OS Version     : Linux 4.15
NodeJS Version : v12.14.1
NPM Version    : 6.13.4

[kamilmysliwiec]

Fixed in 0.0.2. Thanks!