Add SimplifyDeep type (#882)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.d.ts

@@ -61,6 +61,7 @@ export type {SetReturnType} from './source/set-return-type';
 export type {SetParameterType} from './source/set-parameter-type';
 export type {Asyncify} from './source/asyncify';
 export type {Simplify} from './source/simplify';
+export type {SimplifyDeep} from './source/simplify-deep';
 export type {Jsonify} from './source/jsonify';
 export type {Jsonifiable} from './source/jsonifiable';
 export type {Schema} from './source/schema';

readme.md

@@ -173,6 +173,7 @@ Click the type names for complete docs.
 - [`SetReturnType`](source/set-return-type.d.ts) - Create a function type with a return type of your choice and the same parameters as the given function type.
 - [`SetParameterType`](source/set-parameter-type.d.ts) - Create a function that replaces some parameters with the given parameters.
 - [`Simplify`](source/simplify.d.ts) - Useful to flatten the type output to improve type hints shown in editors. And also to transform an interface into a type to aide with assignability.
+- [`SimplifyDeep`](source/simplify-deep.d.ts) - Deeply simplifies an object type.
 - [`Get`](source/get.d.ts) - Get a deeply-nested property from an object using a key path, like [Lodash's `.get()`](https://lodash.com/docs/latest#get) function.
 - [`StringKeyOf`](source/string-key-of.d.ts) - Get keys of the given type as strings.
 - [`Schema`](source/schema.d.ts) - Create a deep version of another object type where property values are recursively replaced into a given value type.

source/merge-deep.d.ts

@@ -11,11 +11,7 @@ import type {
 } from './internal';
 import type {UnknownRecord} from './unknown-record';
 import type {EnforceOptional} from './enforce-optional';
-
-/**
-Deeply simplifies an object excluding iterables and functions. Used internally to improve the UX and accept both interfaces and type aliases as inputs.
-*/
-export type SimplifyDeep<Type> = ConditionalSimplifyDeep<Type, Function | Iterable<unknown>, object>;
+import type {SimplifyDeep} from './simplify-deep';
 
 /**
 Try to merge two record properties or return the source property value, preserving `undefined` properties values in both cases.

source/omit-deep.d.ts

@@ -3,9 +3,9 @@ import type {ExactKey, IsArrayReadonly, NonRecursiveType, SetArrayAccess, ToStri
 import type {IsEqual} from './is-equal';
 import type {IsNever} from './is-never';
 import type {LiteralUnion} from './literal-union';
-import type {SimplifyDeep} from './merge-deep';
 import type {Paths} from './paths';
 import type {SharedUnionFieldsDeep} from './shared-union-fields-deep';
+import type {SimplifyDeep} from './simplify-deep';
 import type {UnknownArray} from './unknown-array';
 
 /**

source/simplify-deep.d.ts

@@ -0,0 +1,51 @@
+import type {ConditionalSimplifyDeep} from './conditional-simplify';
+
+/**
+Deeply simplifies an object type.
+
+Useful to flatten the type output to improve type hints shown in editors.
+
+@example
+```
+import type {SimplifyDeep} from 'type-fest';
+
+type Properties1 = {
+	height: number;
+	position: {
+		top: number;
+		bottom: number;
+	};
+};
+
+type Properties2 = {
+	width: number;
+	position: {
+		left: number;
+		right: number;
+	};
+};
+
+type Properties = Properties1 & Properties2;
+// In your editor, hovering over `Props` will show the following:
+//
+// type Properties = Properties1 & Properties2;
+
+type SimplifyDeepProperties = SimplifyDeep<Properties1 & Properties2>;
+// But if wrapped in SimplifyDeep, hovering over `Props` will show a flattened object with all the properties:
+//
+// SimplifyDeepProperties = {
+// 	height: number;
+// 	width: number;
+// 	position: {
+// 		top: number;
+// 		bottom: number;
+// 		left: number;
+// 		right: number;
+// 	};
+// };
+```
+
+@see Simplify
+@category Object
+*/
+export type SimplifyDeep<Type> = ConditionalSimplifyDeep<Type, Function | Iterable<unknown>, object>;

source/simplify.d.ts

@@ -52,7 +52,7 @@ fn(someInterface as Simplify<SomeInterface>); // Good: transform an `interface`
 ```
 
 @link https://github.com/microsoft/TypeScript/issues/15300
-
+@see SimplifyDeep
 @category Object
 */
 export type Simplify<T> = {[KeyType in keyof T]: T[KeyType]} & {};

test-d/simplify-deep.ts

@@ -0,0 +1,31 @@
+import {expectType} from 'tsd';
+import type {SimplifyDeep} from '../index';
+
+type Properties1 = {
+	height: number;
+	position: {
+		top: number;
+		bottom: number;
+	};
+};
+
+type Properties2 = {
+	width: number;
+	position: {
+		left: number;
+		right: number;
+	};
+};
+
+// Flatten the type output to improve type hints shown in editors.
+declare const flattenProperties: {
+	height: number;
+	width: number;
+	position: {
+		top: number;
+		bottom: number;
+		left: number;
+		right: number;
+	};
+};
+expectType<SimplifyDeep<Properties1 & Properties2>>(flattenProperties);