Add RenameKeys type

index.d.ts

@@ -102,6 +102,7 @@ export type {KeyAsString} from './source/key-as-string.d.ts';
 export type {Exact} from './source/exact.d.ts';
 export type {ReadonlyTuple} from './source/readonly-tuple.d.ts';
 export type {OverrideProperties} from './source/override-properties.d.ts';
+export type {RenameKeys} from './source/rename-keys.d.ts';
 export type {OptionalKeysOf} from './source/optional-keys-of.d.ts';
 export type {IsOptionalKeyOf} from './source/is-optional-key-of.d.ts';
 export type {HasOptionalKeys} from './source/has-optional-keys.d.ts';

readme.md

@@ -121,6 +121,7 @@ Click the type names for complete docs.
 - [`MergeDeep`](source/merge-deep.d.ts) - Merge two objects or two arrays/tuples recursively into a new type.
 - [`MergeExclusive`](source/merge-exclusive.d.ts) - Create a type that has mutually exclusive keys.
 - [`OverrideProperties`](source/override-properties.d.ts) - Override existing properties of the given type. Similar to `Merge`, but enforces that the original type has the properties you want to override.
+- [`RenameKeys`](source/rename-keys.d.ts) - Rename keys in an object type according to a map of old-to-new names. Keys absent from the map are returned unchanged. The value type, the optional modifier, and the readonly modifier are applied to the new key.
 - [`RequireAtLeastOne`](source/require-at-least-one.d.ts) - Create a type that requires at least one of the given keys, while keeping the remaining keys as is.
 - [`RequireExactlyOne`](source/require-exactly-one.d.ts) - Create a type that requires exactly one of the given keys and disallows more, while keeping the remaining keys as is.
 - [`RequireAllOrNone`](source/require-all-or-none.d.ts) - Create a type that requires all of the given keys or none of the given keys, while keeping the remaining keys as is.

source/rename-keys.d.ts

@@ -0,0 +1,171 @@
+import type {IsLiteral} from './is-literal.d.ts';
+import type {IsAny} from './is-any.d.ts';
+import type {IsNever} from './is-never.d.ts';
+import type {IsReadonlyKeyOf} from './is-readonly-key-of.d.ts';
+import type {IsOptionalKeyOf} from './is-optional-key-of.d.ts';
+import type {OmitIndexSignature} from './omit-index-signature.d.ts';
+import type {PickIndexSignature} from './pick-index-signature.d.ts';
+import type {Simplify} from './simplify.d.ts';
+import type {IsExactOptionalPropertyTypesEnabled} from './internal/type.d.ts';
+
+/**
+Rename keys in an object type according to a map of old-to-new names. Keys absent from the map are returned unchanged. The value type, the optional modifier, and the readonly modifier are applied to the new key.
+
+Distributes over a union of rename maps and over a union of source types.
+
+When multiple source keys map to the same target, the target's value type is the union of the contributors' value types. The target is optional only when every contributor is optional, and is `readonly` when any contributor is `readonly`. With `exactOptionalPropertyTypes` disabled, the value type of a mixed-optionality merge also includes `undefined`.
+
+A union target distributes, producing one output key per member. For example, `{a: 'b' | 'c'}` on a source with `a: string` produces both `b: string` and `c: string`.
+
+A rename map entry whose key is not a property of the source type is ignored, matching the result of `Omit`. The optional modifier on a rename map entry is ignored, so `{a?: 'alpha'}` produces the same result as `{a: 'alpha'}`.
+
+Returns `never` in the following cases.
+- A rename map entry's value is not a literal `PropertyKey` (rejects primitives like `string`).
+- The source type is `any` or `never`.
+
+@example
+```
+import type {RenameKeys} from 'type-fest';
+
+type User = {
+	id: string;
+	firstName: string;
+	createdAt: Date;
+};
+
+type Renamed = RenameKeys<User, {firstName: 'first_name'; createdAt: 'created_at'}>;
+//=> {id: string; first_name: string; created_at: Date}
+```
+
+@example
+```
+import type {RenameKeys} from 'type-fest';
+
+type SearchInput = {
+	textQuery: string;
+	voiceQuery: Blob;
+	imageQuery: File;
+};
+
+type Normalized = RenameKeys<SearchInput, {textQuery: 'query'; voiceQuery: 'query'; imageQuery: 'query'}>;
+//=> {query: string | Blob | File}
+```
+
+@category Object
+*/
+export type RenameKeys<
+	BaseType,
+	RenameMap extends Record<PropertyKey, PropertyKey>,
+> = IsAny<BaseType> extends true
+	? never
+	: IsNever<BaseType> extends true
+		? never
+		: BaseType extends BaseType // Distribute over union sources.
+			? BaseType extends object
+				? RenameMap extends RenameMap // Distribute over union maps.
+					? _AllTargetsAreLiterals<Required<RenameMap>> extends true
+						? _RenameOnce<BaseType, Required<RenameMap>>
+						: never
+					: never
+				: never
+			: never;
+
+type _AllTargetsAreLiterals<RenameMap> = [
+	{
+		[Key in keyof RenameMap]: IsLiteral<RenameMap[Key]>;
+	}[keyof RenameMap],
+] extends [true]
+	? true
+	: false;
+
+type _TargetOf<SourceKey, RenameMap> =
+	SourceKey extends keyof RenameMap
+		? RenameMap[SourceKey] extends PropertyKey
+			? RenameMap[SourceKey]
+			: SourceKey
+		: SourceKey;
+
+// `BaseType[Key]` on an optional key includes `undefined`. With EOPT on,
+// `Required<Pick>` strips that `undefined`. With EOPT off, the natural
+// index access retains it, so mixed-optionality merges include it.
+type _NewValue<BaseType, Key extends keyof BaseType> =
+	IsExactOptionalPropertyTypesEnabled extends true
+		? Required<Pick<BaseType, Key>>[Key]
+		: BaseType[Key];
+
+// Targets where at least one contributing source key is readonly.
+type _ReadonlyTargets<BaseType extends object, RenameMap> = {
+	[Key in keyof BaseType]: Key extends keyof BaseType
+		? IsReadonlyKeyOf<BaseType, Key> extends true
+			? _TargetOf<Key, RenameMap>
+			: never
+		: never;
+}[keyof BaseType];
+
+// Targets where at least one contributing source key is required.
+type _RequiredTargets<BaseType extends object, RenameMap> = {
+	[Key in keyof BaseType]: Key extends keyof BaseType
+		? IsOptionalKeyOf<BaseType, Key> extends false
+			? _TargetOf<Key, RenameMap>
+			: never
+		: never;
+}[keyof BaseType];
+
+// `Target extends Target` distributes per union member.
+type _RouteTarget<Target, ReadOnly, Required, NeedReadonly extends boolean, NeedRequired extends boolean> =
+	Target extends Target
+		? (Target extends ReadOnly ? true : false) extends NeedReadonly
+			? (Target extends Required ? true : false) extends NeedRequired
+				? Target
+				: never
+			: never
+		: never;
+
+// A literal like `'b'` extends the index signature's `string` key, so
+// routing both through the same fragments misclassifies the literals.
+type _RenameOnce<BaseType extends object, RenameMap> = Simplify<
+	& PickIndexSignature<BaseType>
+	& _RenameLiteralKeys<OmitIndexSignature<BaseType>, RenameMap>
+>;
+
+// TS's key-remapping inherits the first source's modifiers on collision,
+// not "any" or "all". The four fragments specify the modifiers per target.
+type _RenameLiteralKeys<BaseType extends object, RenameMap> =
+	// Readonly and required
+	& {
+		readonly [Key in keyof BaseType as _RouteTarget<
+			_TargetOf<Key, RenameMap>,
+			_ReadonlyTargets<BaseType, RenameMap>,
+			_RequiredTargets<BaseType, RenameMap>,
+			true, true
+		>]-?: _NewValue<BaseType, Key>;
+	}
+	// Readonly and optional
+	& {
+		readonly [Key in keyof BaseType as _RouteTarget<
+			_TargetOf<Key, RenameMap>,
+			_ReadonlyTargets<BaseType, RenameMap>,
+			_RequiredTargets<BaseType, RenameMap>,
+			true, false
+		>]?: _NewValue<BaseType, Key>;
+	}
+	// Mutable and required
+	& {
+		[Key in keyof BaseType as _RouteTarget<
+			_TargetOf<Key, RenameMap>,
+			_ReadonlyTargets<BaseType, RenameMap>,
+			_RequiredTargets<BaseType, RenameMap>,
+			false, true
+		>]-?: _NewValue<BaseType, Key>;
+	}
+	// Mutable and optional
+	& {
+		[Key in keyof BaseType as _RouteTarget<
+			_TargetOf<Key, RenameMap>,
+			_ReadonlyTargets<BaseType, RenameMap>,
+			_RequiredTargets<BaseType, RenameMap>,
+			false, false
+		>]?: _NewValue<BaseType, Key>;
+	};
+
+export {};

test-d/rename-keys.ts

@@ -0,0 +1,202 @@
+import {expectType} from 'tsd';
+import type {RenameKeys} from '../source/rename-keys.d.ts';
+
+// Basic batch rename.
+expectType<{id: string; first_name: string; created_at: Date}>(
+	{} as RenameKeys<{id: string; firstName: string; createdAt: Date}, {firstName: 'first_name'; createdAt: 'created_at'}>,
+);
+
+// Empty rename map is identity.
+expectType<{a: number; b: string}>({} as RenameKeys<{a: number; b: string}, {}>);
+
+// Partial rename, unlisted keys are unchanged.
+expectType<{alpha: number; b: string; c: boolean}>(
+	{} as RenameKeys<{a: number; b: string; c: boolean}, {a: 'alpha'}>,
+);
+
+// `readonly` and optional modifiers are both applied to the new name.
+expectType<{readonly identifier: string; name?: string; count: number}>(
+	{} as RenameKeys<{readonly id: string; label?: string; count: number}, {id: 'identifier'; label: 'name'}>,
+);
+
+// Distributes over a union of rename maps.
+expectType<{x: 1; b: 2} | {a: 1; y: 2}>(
+	{} as RenameKeys<{a: 1; b: 2}, {a: 'x'} | {b: 'y'}>,
+);
+
+// Distributes over a union source type.
+expectType<{kind: 'click'; element: string} | {kind: 'submit'; element: HTMLFormElement}>(
+	{} as RenameKeys<{kind: 'click'; target: string} | {kind: 'submit'; target: HTMLFormElement}, {target: 'element'}>,
+);
+
+// Symbol target key.
+declare const symbolKey: unique symbol;
+type SymbolKey = typeof symbolKey;
+expectType<{[symbolKey]: string; other: number}>(
+	{} as RenameKeys<{tag: string; other: number}, {tag: SymbolKey}>,
+);
+
+// Number target keys.
+expectType<{0: number; 1: string}>(
+	{} as RenameKeys<{first: number; second: string}, {first: 0; second: 1}>,
+);
+
+// A literal target onto a string-indexed object is allowed. The index signature
+// does not preclude adding a named property.
+expectType<{[x: string]: number; b: 1}>(
+	{} as RenameKeys<{[x: string]: number; a: 1}, {a: 'b'}>,
+);
+
+// Swapping two keys is allowed. Both keys rename away simultaneously, so no
+// kept-key collision occurs.
+expectType<{b: 1; a: 2}>({} as RenameKeys<{a: 1; b: 2}, {a: 'b'; b: 'a'}>);
+
+// Renaming a key to itself is a no-op.
+expectType<{a: 1; b: 2}>({} as RenameKeys<{a: 1; b: 2}, {a: 'a'}>);
+
+// Typo'd source key is ignored, matching `Omit`'s result on missing keys.
+expectType<{a: 1; b: 2}>({} as RenameKeys<{a: 1; b: 2}, {nme: 'fullName'}>);
+
+// Optional rename-map entries have the optional modifier ignored.
+expectType<{alpha: number; b: string}>({} as RenameKeys<{a: number; b: string}, {a?: 'alpha'}>);
+
+// Collision with a kept property merges the values into a union.
+expectType<{b: number | string}>({} as RenameKeys<{a: number; b: string}, {a: 'b'}>);
+
+// Cross-union collision merges per union member.
+expectType<{b: number} | {b: string}>({} as RenameKeys<{a: number} | {b: string}, {a: 'b'}>);
+
+// Duplicate targets across the same rename map merge into a union.
+expectType<{x: 1 | 2; c: 3}>({} as RenameKeys<{a: 1; b: 2; c: 3}, {a: 'x'; b: 'x'}>);
+
+// Non-literal targets return `never`. A `string`-typed target would widen to
+// an index signature.
+expectType<never>({} as RenameKeys<{a: number; b: string}, {a: string}>);
+
+// Union targets distribute, producing one output key per member.
+expectType<{b: string; c: string}>({} as RenameKeys<{a: string}, {a: 'b' | 'c'}>);
+
+// Union target preserves modifiers across all expanded keys.
+expectType<{readonly b: string; readonly c: string}>(
+	{} as RenameKeys<{readonly a: string}, {a: 'b' | 'c'}>,
+);
+
+// Preserves optional modifier only when all contributors are optional.
+expectType<{b?: string; c?: string}>({} as RenameKeys<{a?: string}, {a: 'b' | 'c'}>);
+
+// Union target combined with a kept-key collision. Both `b` and `c` are
+// produced, and `b` merges the source's `a` and `b` values.
+expectType<{b: 1 | 2; c: 1}>({} as RenameKeys<{a: 1; b: 2}, {a: 'b' | 'c'}>);
+
+// Union target combined with another source mapping to the same target.
+expectType<{b: string | number; c: number}>(
+	{} as RenameKeys<{a: string; d: number}, {a: 'b'; d: 'b' | 'c'}>,
+);
+
+// Three-member union of rename maps distributes correctly.
+expectType<{x: 1; b: 2; c: 3} | {a: 1; y: 2; c: 3} | {a: 1; b: 2; z: 3}>(
+	{} as RenameKeys<{a: 1; b: 2; c: 3}, {a: 'x'} | {b: 'y'} | {c: 'z'}>,
+);
+
+// `any` source returns `never`. The target key cannot be proven absent from
+// an `any` shape.
+expectType<never>({} as RenameKeys<any, {a: 'x'}>);
+
+// Generic instantiation. The constraint is structural-only, so the type can
+// be used inside other generics without erroring at the definition site.
+type WrappedGeneric<T, K extends keyof T & string> = RenameKeys<T, {[P in K]: `new_${P}`}>;
+expectType<{new_a: number; b: string; new_c: string}>({} as WrappedGeneric<{a: number; b: string; c: string}, 'a' | 'c'>);
+
+// All contributors required.
+expectType<{new_p: string | number | bigint}>(
+	{} as RenameKeys<{p1: string; p2: number; p3: bigint}, {p1: 'new_p'; p2: 'new_p'; p3: 'new_p'}>,
+);
+
+// All contributors optional, optional modifier applies to the target.
+expectType<{new_p?: string | number | bigint}>(
+	{} as RenameKeys<{p1?: string; p2?: number; p3?: bigint}, {p1: 'new_p'; p2: 'new_p'; p3: 'new_p'}>,
+);
+
+// Mixed-optionality merge. The target is required because at least one
+// contributor is required. The value type follows `exactOptionalPropertyTypes`.
+// With EOPT on (as in this test project), the value omits `undefined`.
+expectType<{new_p: string | number | bigint}>(
+	{} as RenameKeys<{p1: string; p2?: number; p3: bigint}, {p1: 'new_p'; p2: 'new_p'; p3: 'new_p'}>,
+);
+
+// Mixed-readonly merge. The target is readonly because at least one
+// contributor is readonly.
+expectType<{readonly new_p: string | number | bigint}>(
+	{} as RenameKeys<{p1: string; readonly p2: number; p3: bigint}, {p1: 'new_p'; p2: 'new_p'; p3: 'new_p'}>,
+);
+
+// Optional source first, required source second. The target is required
+// because a required contributor exists, regardless of source order.
+expectType<{x: number | string}>(
+	{} as RenameKeys<{a?: number; b: string}, {a: 'x'; b: 'x'}>,
+);
+
+// Required source first, optional source second.
+expectType<{x: string | number}>(
+	{} as RenameKeys<{a: string; b?: number}, {a: 'x'; b: 'x'}>,
+);
+
+// Three sources with the optional one in the middle.
+expectType<{z: number | string | bigint}>(
+	{} as RenameKeys<{a: number; b?: string; c: bigint}, {a: 'z'; b: 'z'; c: 'z'}>,
+);
+
+// Three sources with the optional one at the end.
+expectType<{z: number | string | bigint}>(
+	{} as RenameKeys<{a: number; b: string; c?: bigint}, {a: 'z'; b: 'z'; c: 'z'}>,
+);
+
+// Mixed readonly AND mixed optionality. Any readonly contributor results in
+// readonly, any required contributor results in required.
+expectType<{readonly x: string | number}>(
+	{} as RenameKeys<{readonly a?: string; b: number}, {a: 'x'; b: 'x'}>,
+);
+
+// Any readonly contributor with all optional contributors.
+expectType<{readonly x?: string | number}>(
+	{} as RenameKeys<{readonly a?: string; b?: number}, {a: 'x'; b: 'x'}>,
+);
+
+// Union target with mixed optionality across members. The required target
+// is required, the optional-only target is optional.
+expectType<{x: number | string; y?: number}>(
+	{} as RenameKeys<{a?: number; b: string}, {a: 'x' | 'y'; b: 'x'}>,
+);
+
+// Union target where one member collides with a kept required key.
+expectType<{b: number | string; c: number | boolean}>(
+	{} as RenameKeys<{a?: number; b: string; c: boolean}, {a: 'b' | 'c'}>,
+);
+
+// Sources span all four modifier categories simultaneously.
+expectType<{
+	readonly x: 'a-val' | 'b-val';
+	readonly y?: 'b-val' | 'c-val';
+	z: 'd-val';
+}>(
+	{} as RenameKeys<
+		{
+			readonly a: 'a-val';
+			b?: 'b-val';
+			readonly c?: 'c-val';
+			d: 'd-val';
+		},
+		{a: 'x'; b: 'x' | 'y'; c: 'y'; d: 'z'}
+	>,
+);
+
+// Index signature is preserved when the only renamed source is optional. The
+// index sig key must not affect the target's modifier routing.
+expectType<{[x: string]: number; b?: 1}>(
+	{} as RenameKeys<{[x: string]: number; a?: 1}, {a: 'b'}>,
+);
+
+// Three-way swap with the optional source in the middle.
+expectType<{b: 1; c?: 2; a: 3}>(
+	{} as RenameKeys<{a: 1; b?: 2; c: 3}, {a: 'b'; b: 'c'; c: 'a'}>,
+);