.eslintrc.js

module.exports = {
	overrides : [{
		files : [
			"*.svelte",
		],

		extends : [
			"plugin:@ota-meshi/svelte/recommended",
		],

		rules : {
			"no-unused-vars" : [ "warn", {
				args : "after-used",
				ignoreRestSiblings : true,
				caughtErrors : "none",
				varsIgnorePattern : "_",
			}],
		},
	}],
};

component.svelte

{#each { length : 5 } as _}
    <div>thing</div>
{/each}

package.json

{
  "name": "eslint-plugin-svelte-unused-vars",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "lint": "eslint ."
  },
  "devDependencies": {
    "@ota-meshi/eslint-plugin-svelte": "^0.34.0",
    "eslint": "^8.18.0"
  }
}