v4: Preserve function types in .meta() (#4636)

* Preserve function types

* preserve function types

* Support function types in replacer

* Add additional test

---------

Co-authored-by: Colin McDonnell <[email protected]>

Author: samchungy

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

@@ -163,3 +163,33 @@ test("loose examples", () => {
     examples: ["example"],
   });
 });
+
+test("function meta witout replacement", () => {
+  const myReg = z.registry<{
+    defaulter: (arg: string, test: boolean) => number;
+  }>();
+
+  const mySchema = z.date();
+  myReg.add(mySchema, {
+    defaulter: (arg, _test) => {
+      return arg.length;
+    },
+  });
+
+  expect(myReg.get(mySchema)!.defaulter("hello", true)).toEqual(5);
+});
+
+test("function meta with replacement", () => {
+  const myReg = z.registry<{
+    defaulter: (arg: z.$input, test: boolean) => z.$output;
+  }>();
+
+  const mySchema = z.string().transform((val) => val.length);
+  myReg.add(mySchema, {
+    defaulter: (arg, _test) => {
+      return arg.length;
+    },
+  });
+
+  expect(myReg.get(mySchema)!.defaulter("hello", true)).toEqual(5);
+});

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

@@ -12,10 +12,16 @@ export type $replace<Meta, S extends $ZodType> = Meta extends $output
     ? core.input<S>
     : Meta extends (infer M)[]
       ? $replace<M, S>[]
-      : // handle objecs
-        Meta extends object
-        ? { [K in keyof Meta]: $replace<Meta[K], S> }
-        : Meta;
+      : Meta extends (...args: infer P) => infer R
+        ? (
+            ...args: {
+              [K in keyof P]: $replace<P[K], S>; // tuple
+            }
+          ) => $replace<R, S>
+        : // handle objects
+          Meta extends object
+          ? { [K in keyof Meta]: $replace<Meta[K], S> }
+          : Meta;
 
 type MetadataType = Record<string, unknown> | undefined;
 export class $ZodRegistry<Meta extends MetadataType = MetadataType, Schema extends $ZodType = $ZodType> {