prefer-type-fest-set-non-nullable
Require TypeFest SetNonNullable<T, Keys> over imported aliases like
NonNullableBy.
Targeted pattern scopeโ
This rule scopes matching to imported legacy aliases that model the same semantics as SetNonNullable<T, Keys>.
- Type references that resolve to imported
NonNullableByaliases.
Locally defined lookalikes or unrelated type references are excluded unless they resolve to the targeted imported alias.
What this rule reportsโ
This rule reports imported alias usages that should migrate to SetNonNullable<T, Keys>.
- Type references that resolve to imported
NonNullableByaliases.
Why this rule existsโ
SetNonNullable is the canonical TypeFest utility for making selected keys
non-nullable. Standardizing on canonical TypeFest naming keeps utility usage
predictable in public TypeScript codebases.
โ Incorrectโ
import type { NonNullableBy } from "type-aliases";
type PersistedUser = NonNullableBy<User, "id">;
โ Correctโ
import type { SetNonNullable } from "type-fest";
type PersistedUser = SetNonNullable<User, "id">;
Behavior and migration notesโ
SetNonNullable<T, Keys>enforces non-nullability on selected keys while preserving the rest of the shape.- This rule targets imported alias names that duplicate the same semantics (
NonNullableBy). - Use this utility for persisted/entity states where selected fields must be present and non-null after validation.
Additional examplesโ
โ Incorrect โ Additional exampleโ
import type { NonNullableBy } from "type-aliases";
type Persisted = NonNullableBy<User, "id">;
โ Correct โ Additional exampleโ
import type { SetNonNullable } from "type-fest";
type Persisted = SetNonNullable<User, "id">;
โ Correct โ Repository-wide usageโ
type SafeOrder = SetNonNullable<Order, "orderId" | "createdAt">;
ESLint flat config exampleโ
import typefest from "eslint-plugin-typefest";
export default [
{
plugins: { typefest },
rules: {
"typefest/prefer-type-fest-set-non-nullable": "error",
},
},
];
When not to use itโ
Disable this rule if existing exported aliases must remain stable.
Package documentationโ
TypeFest package documentation:
Source file: source/set-non-nullable.d.ts
/**
* Create a type that makes the given keys non-nullable, where the remaining
* keys are kept as is.
*
* If no keys are given, all keys will be made non-nullable.
*
* Use-case: You want to define a single model where the only thing that changes
* is whether or not some or all of the keys are non-nullable.
*
* @category Object
*
* @example
* ```
* import type {SetNonNullable} from 'type-fest';
*
* type Foo = {
* a: number | null;
* b: string | undefined;
* c?: boolean | null;
* };
*
* type SomeNonNullable = SetNonNullable<Foo, 'b' | 'c'>;
* // type SomeNonNullable = {
* // a: number | null;
* // b: string; // Can no longer be undefined.
* // c?: boolean; // Can no longer be null, but is still optional.
* // }
*
* type AllNonNullable = SetNonNullable<Foo>;
* // type AllNonNullable = {
* // a: number; // Can no longer be null.
* // b: string; // Can no longer be undefined.
* // c?: boolean; // Can no longer be null, but is still optional.
* // }
* ```;
*/
Rule catalog ID: R062