Loose signature for index signature shapes

Author: colinhacks

packages/zod/src/v4/classic/tests/object.test.ts

@@ -516,3 +516,17 @@ test("zodtype assignability", () => {
   // @ts-expect-error
   z.object({ hello: z.number() }) satisfies z.ZodType<{ hello?: string | undefined }>;
 });
+
+test("index signature in shape", () => {
+  function makeZodObj<const T extends string>(key: T) {
+    return z.looseObject({
+      [key]: z.string(),
+    });
+  }
+
+  const schema = makeZodObj("foo");
+  type schema = z.infer<typeof schema>;
+  schema.parse({}).asdf;
+
+  expectTypeOf<schema>().toEqualTypeOf<Record<string, unknown>>();
+});

packages/zod/src/v4/core/schemas.ts

@@ -1527,7 +1527,7 @@ type OptionalOutSchema = { _zod: { optout: "optional" } };
 type OptionalInSchema = { _zod: { optin: "optional" } };
 
 export type $InferObjectOutput<T extends $ZodLooseShape, Extra extends Record<string, unknown>> = string extends keyof T
-  ? object
+  ? Record<string, unknown>
   : keyof (T & Extra) extends never
     ? Record<string, never>
     : util.Prettify<
@@ -1539,7 +1539,7 @@ export type $InferObjectOutput<T extends $ZodLooseShape, Extra extends Record<st
       >;
 
 export type $InferObjectInput<T extends $ZodLooseShape, Extra extends Record<string, unknown>> = string extends keyof T
-  ? object
+  ? Record<string, unknown>
   : keyof (T & Extra) extends never
     ? Record<string, never>
     : util.Prettify<

play.ts

@@ -7,3 +7,20 @@ console.dir(nativeEnumSchema.safeParse("a"), { depth: null }); // Valid
 console.dir(nativeEnumSchema.safeParse("d"), { depth: null }); // Throws ZodError
 
 z.file().mime([""]);
+
+// function makeZodObj<const T extends string>(key: T) {
+//   const a: string = "a";
+//   const b: string = "b";
+//   return z.looseObject({
+//     [a]: z.string(),
+//     [b]: z.number(),
+//   });
+// }
+
+function makeZodObj<K extends string>(key: K) {
+  return z.record(z.literal(key), z.string());
+}
+
+const schema = makeZodObj("foo");
+type schema = z.infer<typeof schema>;
+// { foo: string; }