feat: add type for inferring all variants of a transformer

Author: thetutlage

src/types.ts

@@ -13,6 +13,7 @@ import { type ContainerResolver } from '@adonisjs/fold'
 import type { Item } from './resource/item.ts'
 import { type Paginator } from './paginator.ts'
 import type { Collection } from './resource/collection.ts'
+import { type BaseTransformer } from './base_transformer.ts'
 
 /**
  * Counter to increment the depth. At max we will allow fetching
@@ -434,6 +435,42 @@ export type InferData<
   ? UnpackValues<Awaited<ReturnType<Transformer[Variant]>>, MaxDepth, Depth, false>
   : never
 
+/**
+ * Infers the data structure for all variant methods of a transformer class, excluding
+ * the default 'toObject' method and base transformer methods.
+ *
+ * @template Transformer - The resource class to infer variant data from
+ * @template MaxDepth - Maximum depth allowed for unpacking (defaults to -1 for unlimited)
+ * @template Depth - Current depth level (defaults to 0)
+ *
+ * @example
+ * ```typescript
+ * class UserResource {
+ *   toObject() { return { id: 1, name: "John" } }
+ *   toSummary() { return { id: 1 } }
+ *   toProfile() { return { id: 1, name: "John", email: "john@example.com" } }
+ * }
+ *
+ * type UserVariants = InferVariants<UserResource>
+ * // Result: {
+ * //   toSummary: { id: number }
+ * //   toProfile: { id: number; name: string; email: string }
+ * // }
+ * ```
+ */
+export type InferVariants<Transformer, MaxDepth extends number = -1, Depth extends number = 0> = {
+  [O in {
+    [K in keyof Transformer]: 'toObject' extends K
+      ? never
+      : K extends keyof BaseTransformer<any>
+        ? never
+        : Transformer[K] extends (...args: any[]) => unknown
+          ? K
+          : never
+  }[keyof Transformer] &
+    string]: InferData<Transformer, O, MaxDepth, Depth>
+}
+
 /**
  * Function interface for the main serialize function that handles different data types.
  * Provides overloads for serializing Items, Collections, Paginators, and resource data.

tests/types.spec.ts

@@ -10,7 +10,7 @@
 import { test } from '@japa/runner'
 import { debug } from '../src/debug.ts'
 import { serialize } from '../src/serialize.ts'
-import { type InferData } from '../src/types.ts'
+import { type InferVariants, type InferData } from '../src/types.ts'
 import { User } from './fixtures/models/user.ts'
 import { Post } from './fixtures/models/posts.ts'
 import { Email } from './fixtures/models/email.ts'
@@ -232,4 +232,30 @@ test.group('Types | Fixtures', () => {
     }>()
     expectTypeOf(emailDataObject).toEqualTypeOf<EmailData>()
   })
+
+  test('infer all variants of a transformer', async ({ expectTypeOf }) => {
+    const user = new User()
+    const userTransformer = new UserTransformer(user)
+    const userDataObject = await serialize(UserTransformer.transform(user).useVariant('basicInfo'))
+
+    type UserData = InferVariants<typeof userTransformer>
+    debug('%O', userDataObject)
+
+    expectTypeOf<UserData>().toEqualTypeOf<{
+      basicInfo: {
+        id: number
+        name: string
+        profile?:
+          | {
+              id: number
+              twitterHandle: string | null
+              githubUsername: string | null
+            }
+          | null
+          | undefined
+      }
+    }>()
+
+    expectTypeOf(userDataObject).toEqualTypeOf<UserData['basicInfo']>()
+  })
 })