WIP

src/@types/enum-types.ts

@@ -3,7 +3,7 @@ export type EnumOrObject = Record<string | number, string | number>;
 
 /**
  * Utility type to extract the enum values from a `const object`,
- * or convert an `enum` object produced by `typeof Enum` into the union type representing its values.
+ * or convert an `enum` interface produced by `typeof Enum` into the union type representing its values.
  */
 export type EnumValues<E> = E[keyof E];
 
@@ -12,43 +12,7 @@ export type EnumValues<E> = E[keyof E];
  * @example
  * TSNumericEnum<typeof WeatherType>
  */
-// NB: this works because `EnumValues<typeof Enum>` returns the underlying Enum union type.
 export type TSNumericEnum<T extends EnumOrObject> = number extends EnumValues<T> ? T : never;
 
 /** Generic type constraint representing a non reverse-mapped TS enum or `const object`. */
 export type NormalEnum<T extends EnumOrObject> = Exclude<T, TSNumericEnum<T>>;
-
-// ### Type check tests
-
-enum testEnumNum {
-  testN1 = 1,
-  testN2 = 2,
-}
-
-enum testEnumString {
-  testS1 = "apple",
-  testS2 = "banana",
-}
-
-const testObjNum = { testON1: 1, testON2: 2 } as const;
-
-const testObjString = { testOS1: "apple", testOS2: "banana" } as const;
-
-testEnumNum satisfies EnumOrObject;
-testEnumString satisfies EnumOrObject;
-testObjNum satisfies EnumOrObject;
-testObjString satisfies EnumOrObject;
-
-// @ts-expect-error - This is intentionally supposed to fail as an example
-testEnumNum satisfies NormalEnum<typeof testEnumNum>;
-testEnumString satisfies NormalEnum<typeof testEnumString>;
-testObjNum satisfies NormalEnum<typeof testObjNum>;
-testObjString satisfies NormalEnum<typeof testObjString>;
-
-testEnumNum satisfies TSNumericEnum<typeof testEnumNum>;
-// @ts-expect-error - This is intentionally supposed to fail as an example
-testEnumString satisfies TSNumericEnum<typeof testEnumString>;
-// @ts-expect-error - This is intentionally supposed to fail as an example
-testObjNum satisfies TSNumericEnum<typeof testObjNum>;
-// @ts-expect-error - This is intentionally supposed to fail as an example
-testObjString satisfies TSNumericEnum<typeof testObjString>;

src/utils/enums.ts

@@ -38,7 +38,7 @@ export function getEnumKeys<E extends EnumOrObject>(enumType: TSNumericEnum<E>):
  * @remarks
  * To retrieve the keys of a {@linkcode NormalEnum}, use {@linkcode Object.values} instead.
  */
-// NB: This does not use `EnumValues<E>` as it messes with variable highlighting in IDEs.
+// NB: This intentionally does not use `EnumValues<E>` as using `E[keyof E]` leads to improved variable highlighting in IDEs.
 export function getEnumValues<E extends EnumOrObject>(enumType: TSNumericEnum<E>): E[keyof E][] {
   return Object.values(enumType).filter(v => typeof v !== "string") as E[keyof E][];
 }
@@ -59,7 +59,10 @@ export function getEnumValues<E extends EnumOrObject>(enumType: TSNumericEnum<E>
  * @remarks
  * If multiple keys map to the same value, the first one (in insertion order) will be retrieved.
  */
-export function enumValueToKey<T extends EnumOrObject>(object: NormalEnum<T>, val: EnumValues<T>): keyof T {
+export function enumValueToKey<T extends EnumOrObject, V extends EnumValues<T>>(
+  object: NormalEnum<T>,
+  val: V,
+): keyof T {
   for (const [key, value] of Object.entries(object)) {
     if (val === value) {
       return key;

test/types/enum-types.test-d.ts

@@ -0,0 +1,101 @@
+import type { EnumOrObject, EnumValues, TSNumericEnum, NormalEnum } from "#app/@types/enum-types";
+
+import type { getEnumKeys, getEnumValues } from "#app/utils/enums";
+import { enumValueToKey } from "#app/utils/enums";
+
+import { expectTypeOf, describe, it } from "vitest";
+
+enum testEnumNum {
+  testN1 = 1,
+  testN2 = 2,
+}
+
+enum testEnumString {
+  testS1 = "apple",
+  testS2 = "banana",
+}
+
+const testObjNum = { testON1: 1, testON2: 2 } as const;
+
+const testObjString = { testOS1: "apple", testOS2: "banana" } as const;
+
+describe("Enum Type Helpers", () => {
+  describe("EnumValues", () => {
+    it("should go from enum object type to value type", () => {
+      expectTypeOf<EnumValues<typeof testEnumNum>>().toEqualTypeOf<testEnumNum>();
+      expectTypeOf<EnumValues<typeof testEnumNum>>().branded.toEqualTypeOf<1 | 2>();
+
+      expectTypeOf<EnumValues<typeof testEnumString>>().toEqualTypeOf<testEnumString>();
+      expectTypeOf<EnumValues<typeof testEnumString>>().toEqualTypeOf<testEnumString.testS1 | testEnumString.testS2>();
+      expectTypeOf<EnumValues<typeof testEnumString>>().toMatchTypeOf<"apple" | "banana">();
+    });
+
+    it("should produce union of const object values as type", () => {
+      expectTypeOf<EnumValues<typeof testObjNum>>().toEqualTypeOf<1 | 2>();
+
+      expectTypeOf<EnumValues<typeof testObjString>>().toEqualTypeOf<"apple" | "banana">();
+    });
+  });
+
+  describe("TSNumericEnum", () => {
+    it("should match numeric enums", () => {
+      expectTypeOf<TSNumericEnum<typeof testEnumNum>>().toEqualTypeOf<typeof testEnumNum>();
+    });
+
+    it("should not match string enums or const objects", () => {
+      expectTypeOf<TSNumericEnum<typeof testEnumString>>().toBeNever();
+      expectTypeOf<TSNumericEnum<typeof testObjNum>>().toBeNever();
+      expectTypeOf<TSNumericEnum<typeof testObjString>>().toBeNever();
+    });
+  });
+
+  describe("NormalEnum", () => {
+    it("should match string enums or const objects", () => {
+      expectTypeOf<NormalEnum<typeof testEnumString>>().toEqualTypeOf<typeof testEnumString>();
+      expectTypeOf<NormalEnum<typeof testObjNum>>().toEqualTypeOf<typeof testObjNum>();
+      expectTypeOf<NormalEnum<typeof testObjString>>().toEqualTypeOf<typeof testObjString>();
+    });
+    it("should not match numeric enums", () => {
+      expectTypeOf<NormalEnum<typeof testEnumNum>>().toBeNever();
+    });
+  });
+
+  describe("EnumOrObject", () => {
+    it("should match any enum or const object", () => {
+      expectTypeOf<typeof testEnumNum>().toMatchTypeOf<EnumOrObject>();
+      expectTypeOf<typeof testEnumString>().toMatchTypeOf<EnumOrObject>();
+      expectTypeOf<typeof testObjNum>().toMatchTypeOf<EnumOrObject>();
+      expectTypeOf<typeof testObjString>().toMatchTypeOf<EnumOrObject>();
+    });
+
+    it("should not match an enum value union w/o typeof", () => {
+      expectTypeOf<testEnumNum>().not.toMatchTypeOf<EnumOrObject>();
+      expectTypeOf<testEnumString>().not.toMatchTypeOf<EnumOrObject>();
+    });
+
+    it("should be equivalent to `TSNumericEnum | NormalEnum`", () => {
+      expectTypeOf<EnumOrObject>().branded.toEqualTypeOf<TSNumericEnum<EnumOrObject> | NormalEnum<EnumOrObject>>();
+    });
+  });
+});
+
+describe("Enum Functions", () => {
+  describe("getEnumKeys", () => {
+    it("should retrieve keys of numeric enum", () => {
+      expectTypeOf<typeof getEnumKeys<typeof testEnumNum>>().returns.toEqualTypeOf<("testN1" | "testN2")[]>();
+    });
+  });
+
+  describe("getEnumValues", () => {
+    it("should retrieve values of numeric enum", () => {
+      expectTypeOf<typeof getEnumValues<typeof testEnumNum>>().returns.branded.toEqualTypeOf<(1 | 2)[]>();
+    });
+  });
+
+  describe("enumValueToKey", () => {
+    it("should retrieve values for a given key", () => {
+      // @ts-expect-error oopsie
+      expectTypeOf(enumValueToKey(testEnumString, testEnumString.testS1)).toEqualTypeOf<"testS1">();
+    });
+  });
+});

vitest.config.ts

@@ -28,19 +28,23 @@ export default defineProject(({ mode }) => ({
         }
       },
     },
-    environment: "jsdom" as const,
+    environment: "jsdom",
     environmentOptions: {
       jsdom: {
         resources: "usable",
       },
     },
+    typecheck: {
+      tsconfig: "tsconfig.json",
+      include: ["./test/types/**/*.{test,spec}{-|.}d.ts"],
+    },
     threads: false,
     trace: true,
     restoreMocks: true,
     watch: false,
     coverage: {
-      provider: "istanbul" as const,
-      reportsDirectory: "coverage" as const,
+      provider: "istanbul",
+      reportsDirectory: "coverage",
       reporters: ["text-summary", "html"],
     },
     name: "main",