type-fest/source/paths.d.ts

A collection of essential TypeScript types

import type {StaticPartOfArray, VariablePartOfArray, NonRecursiveType, ToString, IsNumberLike} from './internal';
import type {EmptyObject} from './empty-object';
import type {IsAny} from './is-any';
import type {UnknownArray} from './unknown-array';
import type {Subtract} from './subtract';
import type {GreaterThan} from './greater-than';

/**
Paths options.

@see {@link Paths}
*/
export type PathsOptions = {
	/**
	The maximum depth to recurse when searching for paths.

	@default 10
	*/
	maxRecursionDepth?: number;

	/**
	Use bracket notation for array indices and numeric object keys.

	@default false

	@example
	```
	type ArrayExample = {
		array: ['foo'];
	};

	type A = Paths<ArrayExample, {bracketNotation: false}>;
	//=> 'array' | 'array.0'

	type B = Paths<ArrayExample, {bracketNotation: true}>;
	//=> 'array' | 'array[0]'
	```

	@example
	```
	type NumberKeyExample = {
		1: ['foo'];
	};

	type A = Paths<NumberKeyExample, {bracketNotation: false}>;
	//=> 1 | '1' | '1.0'

	type B = Paths<NumberKeyExample, {bracketNotation: true}>;
	//=> '[1]' | '[1][0]'
	```
	*/
	bracketNotation?: boolean;
};

type DefaultPathsOptions = {
	maxRecursionDepth: 10;
	bracketNotation: false;
};

/**
Generate a union of all possible paths to properties in the given object.

It also works with arrays.

Use-case: You want a type-safe way to access deeply nested properties in an object.

@example
```
import type {Paths} from 'type-fest';

type Project = {
	filename: string;
	listA: string[];
	listB: [{filename: string}];
	folder: {
		subfolder: {
			filename: string;
		};
	};
};

type ProjectPaths = Paths<Project>;
//=> 'filename' | 'listA' | 'listB' | 'folder' | `listA.${number}` | 'listB.0' | 'listB.0.filename' | 'folder.subfolder' | 'folder.subfolder.filename'

declare function open<Path extends ProjectPaths>(path: Path): void;

open('filename'); // Pass
open('folder.subfolder'); // Pass
open('folder.subfolder.filename'); // Pass
open('foo'); // TypeError

// Also works with arrays
open('listA.1'); // Pass
open('listB.0'); // Pass
open('listB.1'); // TypeError. Because listB only has one element.
```

@category Object
@category Array
*/
export type Paths<T, Options extends PathsOptions = {}> = _Paths<T, {
	// Set default maxRecursionDepth to 10
	maxRecursionDepth: Options['maxRecursionDepth'] extends number ? Options['maxRecursionDepth'] : DefaultPathsOptions['maxRecursionDepth'];
	// Set default bracketNotation to false
	bracketNotation: Options['bracketNotation'] extends boolean ? Options['bracketNotation'] : DefaultPathsOptions['bracketNotation'];
}>;

type _Paths<T, Options extends Required<PathsOptions>> =
	T extends NonRecursiveType | ReadonlyMap<unknown, unknown> | ReadonlySet<unknown>
		? never
		: IsAny<T> extends true
			? never
			: T extends UnknownArray
				? number extends T['length']
					// We need to handle the fixed and non-fixed index part of the array separately.
					? InternalPaths<StaticPartOfArray<T>, Options>
					| InternalPaths<Array<VariablePartOfArray<T>[number]>, Options>
					: InternalPaths<T, Options>
				: T extends object
					? InternalPaths<T, Options>
					: never;

type InternalPaths<T, Options extends Required<PathsOptions>> =
	Options['maxRecursionDepth'] extends infer MaxDepth extends number
		? Required<T> extends infer T
			? T extends EmptyObject | readonly []
				? never
				: {
					[Key in keyof T]:
					Key extends string | number // Limit `Key` to string or number.
						? (
							Options['bracketNotation'] extends true
								? IsNumberLike<Key> extends true
									? `[${Key}]`
									: (Key | ToString<Key>)
								: never
								|
								Options['bracketNotation'] extends false
								// If `Key` is a number, return `Key | `${Key}``, because both `array[0]` and `array['0']` work.
									? (Key | ToString<Key>)
									: never
						) extends infer TranformedKey extends string | number ?
						// 1. If style is 'a[0].b' and 'Key' is a numberlike value like 3 or '3', transform 'Key' to `[${Key}]`, else to `${Key}` | Key
						// 2. If style is 'a.0.b', transform 'Key' to `${Key}` | Key
							| TranformedKey
							| (
								// Recursively generate paths for the current key
								GreaterThan<MaxDepth, 0> extends true // Limit the depth to prevent infinite recursion
									? _Paths<T[Key], {bracketNotation: Options['bracketNotation']; maxRecursionDepth: Subtract<MaxDepth, 1>}> extends infer SubPath
										? SubPath extends string | number
											? (
												Options['bracketNotation'] extends true
													? SubPath extends `[${any}]` | `[${any}]${string}`
														? `${TranformedKey}${SubPath}` // If next node is number key like `[3]`, no need to add `.` before it.
														: `${TranformedKey}.${SubPath}`
													: never
											) | (
												Options['bracketNotation'] extends false
													? `${TranformedKey}.${SubPath}`
													: never
											)
											: never
										: never
									: never
							)
							: never
						: never
				}[keyof T & (T extends UnknownArray ? number : unknown)]
			: never
		: never;