prefer-type-fest-non-empty-tuple
Require TypeFest NonEmptyTuple over the ad-hoc readonly [T, ...T[]] tuple pattern.
Targeted pattern scopeโ
This rule targets ad-hoc tuple-rest patterns that encode non-empty collections.
What this rule reportsโ
readonly [T, ...T[]]
Why this rule existsโ
NonEmptyTuple<T> is a well-known TypeFest alias that communicates the intent of a non-empty tuple and keeps shared utility-type usage consistent across codebases.
โ Incorrectโ
type Names = readonly [string, ...string[]];
โ Correctโ
type Names = NonEmptyTuple<string>;
Behavior and migration notesโ
NonEmptyTuple<T>represents tuple/list contracts with at least one element.- This rule targets the explicit rest-tuple spelling (
readonly [T, ...T[]]). - Keep element type aliases explicit when non-empty constraints are part of public API contracts.
Additional examplesโ
โ Incorrect โ Additional exampleโ
type Names = readonly [string, ...string[]];
โ Correct โ Additional exampleโ
type Names = NonEmptyTuple<string>;
โ Correct โ Repository-wide usageโ
type Steps = NonEmptyTuple<{ id: string }>;
ESLint flat config exampleโ
import typefest from "eslint-plugin-typefest";
export default [
{
plugins: { typefest },
rules: {
"typefest/prefer-type-fest-non-empty-tuple": "error",
},
},
];
When not to use itโ
Disable this rule if existing tuple spellings must remain for public compatibility.
Package documentationโ
TypeFest package documentation:
Source file: source/non-empty-tuple.d.ts
/**
* Matches any non-empty tuple.
*
* @category Array
*
* @example
* ```
* import type {NonEmptyTuple} from 'type-fest';
*
* const sum = (...numbers: NonEmptyTuple<number>) => numbers.reduce((total, value) => total + value, 0);
*
* sum(1, 2, 3);
* // Ok
*
* // @ts-expect-error
* sum();
* // Error: Expected at least 1 arguments, but got 0.
* ```;
*
* @see {@link RequireAtLeastOne} for objects
*/
Rule catalog ID: R050