unicorn/no-useless-collection-argument

new Set(), new Map(), new WeakSet() and new WeakMap() make an empty collection when they get no argument, undefined or null. So new Set([]) passes an array for nothing, and the fallback in new Set(items ?? []) never changes the result.

The rule reports [], "", null and undefined, either as the only argument or on the right of ??.

--fix-suggestions removes the argument or the fallback.

Configure

Off by default. To turn it on:

[lint.rules]
"unicorn/no-useless-collection-argument" = "error" # or "warn"

Examples

Reported:

const seen = new Set([]);
const cache = new Map(undefined);

function unique(items) {
  return new Set(items ?? []);
}

Not reported:

const seen = new Set();
const cache = new Map();

function unique(items) {
  return new Set(items);
}

const defaults = new Set(items ?? ["all"]);