Strong types on resources' props

[leite08]

Hi all! 👋

I wish CDK types had stronger types on resources props - and searched on issues but couldn't find anything related.

Currently, one can define this and only learn its invalid at runtime, when stack is being deployed:

// non-fifo queue, as it doesn't specify `fifo: true`
new Queue(stack, name, {
  contentBasedDeduplication: aBooleanValue, // invalid, only applies to fifo queues
});

Typescript CDK could leverage the language's discriminated unions to avoid errors like the one above at compile time.

For example:

type AbstractQueueProps = {
  queueName?: string;
  retentionPeriod?: Duration;
  // ...other shared queue props
};

type StandardQueueProps = AbstractQueueProps & {
  // ...standard-specific props
  contentBasedDeduplication?: never;
  fifo?: never;
};

type FifoQueueProps = AbstractQueueProps & {
  fifo: true;
  contentBasedDeduplication?: boolean;
  // ...other fifo-specific props
};

type Queue = StandardQueueProps | FifoQueueProps;

I know the doc specifies Only applies to FIFO queues, but even better than doc is a compilation error, like so:

Does anyone know whether there's an issue to address this?

Is anyone interested in such improvement across the codebase?

Edit: fix the type structure introducing AbstractQueueProps

[peterwoodworth]

We can't use union types due to how jsii works to support other languages - however we do often validate props to ensure that the configurations will not conflict and cause failure at deployment. If there's a specific validation we can implement for Queue, we'd love to have an issue tracking that / a PR to fix that