feat(typescript-types): Add Simplify<T, E, I>

packages/typescript-types/README.md

@@ -6,6 +6,18 @@ A utility types library for Typescript.
 
 The types included in this library are categorized by their purpose.
 
+#### Definition Types
+
+| Type                   | Description                                                          |
+| ---------------------- | -------------------------------------------------------------------- |
+| [`Primitive`][]        | A union of the primitive types of TypeScript.                        |
+| [`BuiltIns`][]         | A union of the built-in types of TypeScript.                         |
+| [`NonContainerType`][] | A union of types, whose primary pourpose is not holding other types. |
+
+[`Primitive`]: src/primitive.ts
+[`BuiltIns`]: src/built-ins.ts
+[`NonContainerType`]: src/non-container-type.ts
+
 #### Test Types
 
 | Type                                    | Description                                                                                               |
@@ -36,9 +48,12 @@ The types included in this library are categorized by their purpose.
 
 #### Conversion Types
 
-| Type                              | Description                                                        |
-| --------------------------------- | ------------------------------------------------------------------ |
-| [`KeyPath<T, Separator = '.'>`][] | Converts a `Separator` separated string into a tuple of its parts. |
+| Type                              | Description                                                                                          |
+| --------------------------------- | ---------------------------------------------------------------------------------------------------- |
+| [`KeyPath<T, Separator = '.'>`][] | Converts a `Separator` separated string into a tuple of its parts.                                   |
+| [`Simplify<T, E, I>`][]           | Maps types that extend `I` and not `E` to their properties. Helps diagnostic messages to be clearer. |
+
+[`Simplify<T, E, I>`]: src/simplify.ts
 
 #### Combination Types
 

packages/typescript-types/src/built-ins.ts

@@ -0,0 +1,3 @@
+import type { Primitive } from './primitive.js'
+
+export type BuiltIns = Primitive | void | Date | RegExp

packages/typescript-types/src/non-container-type.ts

@@ -0,0 +1,3 @@
+import type { BuiltIns } from './built-ins.js'
+
+export type NonContainerType = BuiltIns | Function | (new (...arguments_: any[]) => unknown)

packages/typescript-types/src/primitive.ts

@@ -0,0 +1 @@
+export type Primitive = null | undefined | string | number | boolean | symbol | bigint | PropertyKey

packages/typescript-types/src/simplify.ts

@@ -0,0 +1,9 @@
+import type { NonContainerType } from './non-container-type.js'
+
+export type Simplify<T, Exclude = NonContainerType, Include = object> = T extends Exclude
+	? T
+	: T extends Include
+		? {
+				[K in keyof T]: Simplify<T[K], Exclude, Include>
+			}
+		: T

packages/typescript-types/test/simplify.tst.ts

@@ -0,0 +1,44 @@
+import type { Simplify } from '@/simplify.js'
+import { expect } from 'tstyche'
+
+type TyreSize = {
+	radius: number
+	type: 'winter' | 'summer'
+}
+
+type Maker = {
+	maker: string
+}
+
+type TyreMaker = Maker & TyreSize
+
+type SimplifiedTyreMaker = {
+	radius: number
+	type: 'winter' | 'summer'
+	maker: string
+}
+
+expect<TyreMaker>().type.not.toBe<SimplifiedTyreMaker>()
+expect<Simplify<TyreMaker>>().type.toBe<SimplifiedTyreMaker>()
+
+type Train = {
+	wheels: TyreMaker[]
+}
+
+type SimplifiedTrain = {
+	wheels: SimplifiedTyreMaker[]
+}
+
+expect<Train>().type.not.toBe<SimplifiedTrain>()
+expect<Simplify<Train>>().type.toBe<SimplifiedTrain>()
+
+type Car = {
+	wheels: [TyreMaker, TyreMaker]
+}
+
+type SimplifiedCar = {
+	wheels: [SimplifiedTyreMaker, SimplifiedTyreMaker]
+}
+
+expect<Car>().type.not.toBe<SimplifiedCar>()
+expect<Simplify<Car>>().type.toBe<SimplifiedCar>()