Fiexd up tests

src/@types/type-helpers.ts

@@ -2,8 +2,10 @@
  * A collection of custom utility types that aid in type checking and ensuring strict type conformity
  */
 
-// biome-ignore lint/correctness/noUnusedImports: Used in a tsdoc comment
+// biome-ignore-start lint/correctness/noUnusedImports: Used in a tsdoc comment
+import type { EnumValues } from "#app/@types/enum-types";
 import type { AbAttr } from "./ability-types";
+// biome-ignore-end lint/correctness/noUnusedImports: Used in a tsdoc comment
 
 /**
  * Exactly matches the type of the argument, preventing adding additional properties.
@@ -11,7 +13,7 @@ import type { AbAttr } from "./ability-types";
  * ⚠️ Should never be used with `extends`, as this will nullify the exactness of the type.
  *
  * As an example, used to ensure that the parameters of {@linkcode AbAttr.canApply} and {@linkcode AbAttr.getTriggerMessage} are compatible with
- * the type of the apply method
+ * the type of its {@linkcode AbAttr.apply | apply} method.
  *
  * @typeParam T - The type to match exactly
  */
@@ -26,9 +28,18 @@ export type Exact<T> = {
 export type Closed<X> = X;
 
 /**
- * Remove `readonly` from all properties of the provided type
- * @typeParam T - The type to make mutable
+ * Remove `readonly` from all properties of the provided type.
+ * @typeParam T - The type to make mutable.
  */
 export type Mutable<T> = {
   -readonly [P in keyof T]: T[P];
 };
+
+/**
+ * Type helper to obtain the keys associated with a given value inside a `const object`.
+ * @typeParam O - The type of the object
+ * @typeParam V - The type of one of O's values
+ */
+export type InferKeys<O extends Record<keyof any, unknown>, V extends EnumValues<O>> = {
+  [K in keyof O]: O[K] extends V ? K : never;
+}[keyof O];

src/utils/enums.ts

@@ -1,9 +1,10 @@
 import type { EnumOrObject, EnumValues, TSNumericEnum, NormalEnum } from "#app/@types/enum-types";
+import type { InferKeys } from "#app/@types/type-helpers";
 
 /**
  * Return the string keys of an Enum object, excluding reverse-mapped numbers.
- * @param enumType - The numeric enum to retrieve keys for.
- * @returns An ordered array of all of `enumType`'s string keys.
+ * @param enumType - The numeric enum to retrieve keys for
+ * @returns An ordered array of all of `enumType`'s string keys
  * @example
  * enum fruit {
  *   apple = 1,
@@ -23,8 +24,8 @@ export function getEnumKeys<E extends EnumOrObject>(enumType: TSNumericEnum<E>):
 
 /**
  * Return the numeric values of a numeric Enum object, excluding reverse-mapped strings.
- * @param enumType - The enum object to retrieve keys for.
- * @returns An ordered array of all of `enumType`'s number values.
+ * @param enumType - The enum object to retrieve keys for
+ * @returns An ordered array of all of `enumType`'s number values
  * @example
  * enum fruit {
  *   apple = 1,
@@ -46,9 +47,9 @@ export function getEnumValues<E extends EnumOrObject>(enumType: TSNumericEnum<E>
 /**
  * Return the name of the key that matches the given Enum value.
  * Can be used to emulate Typescript reverse mapping for `const object`s or string enums.
- * @param object - The {@linkcode NormalEnum} to check.
- * @param val - The value to get the key of.
- * @returns The name of the key with the specified value.
+ * @param object - The {@linkcode NormalEnum} to check
+ * @param val - The value to get the key of
+ * @returns The name of the key with the specified value
  * @example
  * const thing = {
  *   one: 1,
@@ -57,15 +58,16 @@ export function getEnumValues<E extends EnumOrObject>(enumType: TSNumericEnum<E>
  * console.log(enumValueToKey(thing, 2)); // output: "two"
  * @throws Error if an invalid enum value is passed to the function
  * @remarks
- * If multiple keys map to the same value, the first one (in insertion order) will be retrieved.
+ * If multiple keys map to the same value, the first one (in insertion order) will be retrieved,
+ * but the return type will be the union of ALL their corresponding keys.
  */
 export function enumValueToKey<T extends EnumOrObject, V extends EnumValues<T>>(
   object: NormalEnum<T>,
   val: V,
-): keyof T {
+): InferKeys<T, V> {
   for (const [key, value] of Object.entries(object)) {
     if (val === value) {
-      return key;
+      return key as InferKeys<T, V>;
     }
   }
   throw new Error(`Invalid value passed to \`enumValueToKey\`! Value: ${val}`);

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

@@ -1,7 +1,7 @@
 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 type { enumValueToKey } from "#app/utils/enums";
 
 import { expectTypeOf, describe, it } from "vitest";
 
@@ -94,8 +94,14 @@ describe("Enum Functions", () => {
 
   describe("enumValueToKey", () => {
     it("should retrieve values for a given key", () => {
-      // @ts-expect-error oopsie
-      expectTypeOf(enumValueToKey(testEnumString, testEnumString.testS1)).toEqualTypeOf<"testS1">();
+      expectTypeOf<
+        typeof enumValueToKey<typeof testEnumString, testEnumString.testS1>
+      >().returns.toEqualTypeOf<"testS1">();
+      expectTypeOf<typeof enumValueToKey<typeof testEnumString, testEnumString>>().returns.toEqualTypeOf<
+        "testS1" | "testS2"
+      >();
+      expectTypeOf<typeof enumValueToKey<typeof testObjNum, 1>>().returns.toEqualTypeOf<"testON1">();
+      expectTypeOf<typeof enumValueToKey<typeof testObjNum, 1 | 2>>().returns.toEqualTypeOf<"testON1" | "testON2">();
     });
   });
 });