AllowExcess<T>, InexactOptionals<T>, Untrusted<T>, etc.

utility-types.ts

/* eslint-disable @typescript-eslint/ban-types */

/**
 * Allow object literals to include additional unchecked properties.
 * @see https://www.typescriptlang.org/docs/handbook/2/objects.html#excess-property-checks
 */
// prettier-ignore
export type AllowExcess<T> = T extends object
  ? T extends Array<infer U> ? AllowExcess<U>[]
  : {[K in keyof T]: AllowExcess<T[K]>} & {[key: string]: unknown}
  : T;

/**
 * Make all undefined-typed properties in objects optional, recursively.
 * @see https://www.typescriptlang.org/tsconfig/exactOptionalPropertyTypes.html
 */
// prettier-ignore
export type InexactOptionals<T> = T extends object
  ? T extends Array<infer V> ? InexactOptionals<V>[]
  : {[K in keyof T as undefined extends T[K] ? never : K]: InexactOptionals<T[K]>} &
    {[K in keyof T as undefined extends T[K] ? K : never]?: InexactOptionals<T[K]>}
  : T;

/**
 * Make all null-type properties in objects optional, recursively.
 */
// prettier-ignore
export type OptionalNullables<T> = T extends object
  ? T extends Array<infer V> ? OptionalNullables<V>[]
  : {[K in keyof T as null extends T[K] ? never : K]:  OptionalNullables<T[K]>} &
    {[K in keyof T as null extends T[K] ? K : never]?: OptionalNullables<T[K]>}
  : T;

/**
 * Make all undefined-type properties in objects nullable, recursively.
 */
// prettier-ignore
export type NullableOptionals<T> = T extends object
  ? T extends Array<infer V> ? NullableOptionals<V>[]
  : {[K in keyof T as undefined extends T[K] ? never : K]:  NullableOptionals<T[K]> | null} &
    {[K in keyof T as undefined extends T[K] ? K : never]?: NullableOptionals<T[K]> | null}
  : T;

/**
 * Make intellisense on complex objects simpler, recursively.
 * @see https://www.totaltypescript.com/concepts/the-prettify-helper
 */
// prettier-ignore
export type Pretty<T> = T extends object ? {[K in keyof T]: Pretty<T[K]>} & {} : T;

/**
 * Make all properties in objects optional, recursively.
 */
// prettier-ignore
export type Untrusted<T> = T extends object
	? T extends Array<infer ValueType> ? Untrusted<ValueType>[]
  : {[K in keyof T]?: Untrusted<T[K]>}
	: T;

/**
 * Make all properties in objects optional and nullable, recursively.
 */
// prettier-ignore
export type UntrustedNullable<T> = T extends object
	? T extends Array<infer ValueType> ? UntrustedNullable<ValueType>[]
  : {[K in keyof T]?: UntrustedNullable<T[K]> | null}
	: T;

cc @Not-Jayden