`z.preprocess()` produces invalid syntax output

[ismailkarsli]

Thanks for the package. While migrating to it, I encountered to an issue. When preprocess is used, the lib produces an invalid output. Here's demonstration:

import { serialize } from "@zod-codepen/zod-v4";
import { z } from "zod";
import { stringToArray } from "./utils.ts";

const Schema = z.object({
	items: z.preprocess((val) => stringToArray(val), z.array(z.string())),
});

const code = serialize(Schema);
// Output:
const generatedCode = z.object({
  items: /* transform */.pipe(z.array(z.string())),
})

[CornWorld]

I'll check this tomorrow

[CornWorld]

I've alreay found the bug, in

zod-codepen/pkgs/core/src/serializer.ts

Lines 1040 to 1047 in af560c8

	builtinHandlers.set("pipe", (schema, ctx) => {
	const def = ctx.adapter.getDef(schema);
	const input = def?.in || def?.innerType;
	const output = def?.out;
	if (!input) return "z.any()";
	const inputStr = ctx.serialize(input);

.
The z.preprocess will return a zod pipe with a zod schema input, and I do not handle that.
I'll fix this soon.

[CornWorld]

I've already troubled in this problem for 2 weeks.
zod-codepen serializes Zod Schema into code strings. For schemas containing callback functions such as transform/preprocess/refine/pipe, serialization functions are required.

However in JS that is a DILEMMA.

fn.toString() only returns the function source code text, not the variable values ​​captured by closures, like:

const factor = 10;
const fn = (x) => x * factor;

fn.toString(); // "(x) => x * factor" // The value 10 of factor is lost

Current Capabilities:

• Pure functions (no external references): can be serialized correctly, by babel plugin
• Closure functions (referencing external variables): cannot be serialized correctly, only placeholders can be used

Shall you give some advice?

[ismailkarsli]

TBH it is not worth it. The external reference can even be dynamic value. How about just making this and calling it a day?

const schema = z.string().pipe(/* function: "(x) => x * factor" */val => val)