Fix any key of inheriting classnames-less component to be never

Author: Andrii Kirmas

src/defs.spec.ts

@@ -70,6 +70,14 @@ describe("ClassNames", () => {
     }
     expect(suites).toBeInstanceOf(Object)
   })
+
+  it("nothing to pick", () => {
+    type NoClassNames = ClassNames<true>
+    const suites: Record<string, ClassNames<NoClassNames>> = {
+      "nothing": {classnames: {}}
+    }
+    expect(suites).toBeInstanceOf(Object)
+  })
 })
 describe("Miss-use", () => {
   it("<'class1', true>", () => {

src/defs.test.ts

@@ -1,5 +1,5 @@
 import { Component } from "react";
-import type { ClassNamesProp, GetClassKeys } from "./defs";
+import type { ClassNamesProp, GetClassKeys, GetClassNames } from "./defs";
 
 class ClassComponent0 extends Component<ClassNamesProp<"comp1"|"comp2">> {}
 
@@ -13,4 +13,44 @@ describe("GetClassKeys", () => {
     }
     expect(suites).toBeInstanceOf(Object)
   })
+
+  it("no classNames", () => {
+      const suites: Record<string, GetClassKeys<{}>> = {
+      //@ts-expect-error is not assignable to type 'never'
+      "undefined": undefined,
+      //@ts-expect-error is not assignable to type 'never'
+      "false": false,
+      //@ts-expect-error is not assignable to type 'never'
+      "null": null,
+      //@ts-expect-error is not assignable to type 'never'
+      "": "",
+      //@ts-expect-error is not assignable to type 'never'
+      "0": 0,
+      //@ts-expect-error is not assignable to type 'never'
+      "{}": {}
+    }
+    expect(suites).toBeInstanceOf(Object)
+  })  
+})
+
+describe("GetClassNames", () => {
+  it("props without classnames", () => {
+
+  const suites: Record<string, GetClassNames<{}>> = {
+    //@ts-expect-error is not assignable to type 'never'
+    "undefined": undefined,
+    //@ts-expect-error is not assignable to type 'never'
+    "false": false,
+    //@ts-expect-error is not assignable to type 'never'
+    "null": null,
+    //@ts-expect-error is not assignable to type 'never'
+    "": "",
+    //@ts-expect-error is not assignable to type 'never'
+    "0": 0,
+    //@ts-expect-error is not assignable to type 'never'
+    "{}": {}
+  }
+  expect(suites).toBeInstanceOf(Object)
 })
+})
+

src/defs.ts

@@ -55,8 +55,8 @@ export type ClassNamesMap<C extends string> = Record<C, ClassValue>
 
 type GetProps<C> = C extends JSXElementConstructor<infer P> ? P : C
 //TODO Consider not empty object
-type GetClassNames<T, K = "classnames", D = EmptyObject> = [T] extends [never] ? D : K extends keyof T ? T[K] : never
-export type GetClassKeys<C> = keyof GetClassNames<GetProps<C>>
+export type GetClassNames<T, D = EmptyObject, K = "classnames"> = [T] extends [never] ? D : K extends keyof T ? T[K] : never
+export type GetClassKeys<C> = [GetClassNames<GetProps<C>, never>] extends [never] ? never : keyof GetClassNames<GetProps<C>>
 
 type Ever<T, V> = [T] extends [never] ? EmptyObject : V
 export type EmptyObject = Record<never, never>
@@ -66,3 +66,4 @@ export type Falsy = undefined|null|false|0|""
 export type ToggleMap<K extends string> = Partial<Record<K, true|Falsy>>
 
 // type get<T, K> = K extends keyof T ? T[K] : never
+