Zod deep strict and `deepPartial` utility

zod-deep-strict-partial.ts

/*
   Copyright 2024, Jaen - https://github.com/jaens

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

import { z, type ZodDiscriminatedUnionOption } from "zod";

const RESOLVING = Symbol("mapOnSchema/resolving");

export function mapOnSchema<T extends z.ZodTypeAny, TResult extends z.ZodTypeAny>(
    schema: T,
    fn: (schema: z.ZodTypeAny) => TResult,
): TResult;

/** 
 * Applies {@link fn} to each element of the schema recursively, replacing every schema with its return value.
 * The rewriting is applied bottom-up (ie. {@link fn} will get called on "children" first).
 */
export function mapOnSchema(schema: z.ZodTypeAny, fn: (schema: z.ZodTypeAny) => z.ZodTypeAny): z.ZodTypeAny {
    // Cache results to support recursive schemas
    const results = new Map<z.ZodTypeAny, z.ZodTypeAny | typeof RESOLVING>();

    function mapElement(s: z.ZodTypeAny) {
        const value = results.get(s);
        if (value === RESOLVING) {
            throw new Error("Recursive schema access detected");
        } else if (value !== undefined) {
            return value;
        }

        results.set(s, RESOLVING);
        const result = mapOnSchema(s, fn);
        results.set(s, result);
        return result;
    }

    function mapInner() {
        if (schema instanceof z.ZodObject) {
            const newShape: Record<string, z.ZodTypeAny> = {};
            for (const [key, value] of Object.entries(schema.shape)) {
                newShape[key] = mapElement(value as z.ZodTypeAny);
            }

            return new z.ZodObject({
                ...schema._def,
                shape: () => newShape,
            });
        } else if (schema instanceof z.ZodArray) {
            return new z.ZodArray({
                ...schema._def,
                type: mapElement(schema._def.type),
            });
        } else if (schema instanceof z.ZodMap) {
            return new z.ZodMap({
                ...schema._def,
                keyType: mapElement(schema._def.keyType),
                valueType: mapElement(schema._def.valueType),
            });
        } else if (schema instanceof z.ZodSet) {
            return new z.ZodSet({
                ...schema._def,
                valueType: mapElement(schema._def.valueType),
            });
        } else if (schema instanceof z.ZodOptional) {
            return new z.ZodOptional({
                ...schema._def,
                innerType: mapElement(schema._def.innerType),
            });
        } else if (schema instanceof z.ZodNullable) {
            return new z.ZodNullable({
                ...schema._def,
                innerType: mapElement(schema._def.innerType),
            });
        } else if (schema instanceof z.ZodDefault) {
            return new z.ZodDefault({
                ...schema._def,
                innerType: mapElement(schema._def.innerType),
            });
        } else if (schema instanceof z.ZodReadonly) {
            return new z.ZodReadonly({
                ...schema._def,
                innerType: mapElement(schema._def.innerType),
            });
        } else if (schema instanceof z.ZodLazy) {
            return new z.ZodLazy({
                ...schema._def,
                // NB: This leaks `fn` into the schema, but there is no other way to support recursive schemas
                getter: () => mapElement(schema._def.getter()),
            });
        } else if (schema instanceof z.ZodBranded) {
            return new z.ZodBranded({
                ...schema._def,
                type: mapElement(schema._def.type),
            });
        } else if (schema instanceof z.ZodEffects) {
            return new z.ZodEffects({
                ...schema._def,
                schema: mapElement(schema._def.schema),
            });
        } else if (schema instanceof z.ZodFunction) {
            return new z.ZodFunction({
                ...schema._def,
                args: schema._def.args.map((arg: z.ZodTypeAny) => mapElement(arg)),
                returns: mapElement(schema._def.returns),
            });
        } else if (schema instanceof z.ZodPromise) {
            return new z.ZodPromise({
                ...schema._def,
                type: mapElement(schema._def.type),
            });
        } else if (schema instanceof z.ZodCatch) {
            return new z.ZodCatch({
                ...schema._def,
                innerType: mapElement(schema._def.innerType),
            });
        } else if (schema instanceof z.ZodTuple) {
            return new z.ZodTuple({
                ...schema._def,
                items: schema._def.items.map((item: z.ZodTypeAny) => mapElement(item)),
                rest: schema._def.rest && mapElement(schema._def.rest),
            });
        } else if (schema instanceof z.ZodDiscriminatedUnion) {
            const optionsMap = new Map(
                [...schema.optionsMap.entries()].map(([k, v]) => [
                    k,
                    mapElement(v) as ZodDiscriminatedUnionOption<string>,
                ]),
            );

            return new z.ZodDiscriminatedUnion({
                ...schema._def,
                options: [...optionsMap.values()],
                optionsMap: optionsMap,
            });
        } else if (schema instanceof z.ZodUnion) {
            return new z.ZodUnion({
                ...schema._def,
                options: schema._def.options.map((option: z.ZodTypeAny) => mapElement(option)),
            });
        } else if (schema instanceof z.ZodIntersection) {
            return new z.ZodIntersection({
                ...schema._def,
                right: mapElement(schema._def.right),
                left: mapElement(schema._def.left),
            });
        } else if (schema instanceof z.ZodRecord) {
            return new z.ZodRecord({
                ...schema._def,
                keyType: mapElement(schema._def.keyType),
                valueType: mapElement(schema._def.valueType),
            });
        } else {
            return schema;
        }
    }

    return fn(mapInner());
}

export function deepPartial<T extends z.ZodTypeAny>(schema: T): T {
    return mapOnSchema(schema, (s) => (s instanceof z.ZodObject ? s.partial() : s)) as T;
}

/** Make all object schemas "strict" (ie. fail on unknown keys), except if they are marked as `.passthrough()` */
export function deepStrict<T extends z.ZodTypeAny>(schema: T): T {
    return mapOnSchema(schema, (s) =>
        s instanceof z.ZodObject && s._def.unknownKeys !== "passthrough" ? s.strict() : s,
    ) as T;
}

export function deepStrictAll<T extends z.ZodTypeAny>(schema: T): T {
    return mapOnSchema(schema, (s) => (s instanceof z.ZodObject ? s.strict() : s)) as T;
}

Just discovered that this function is why my object properties loose their z.describe() values when I use zod-to-openapi to create OpenAPI.

I fixed by adding { ...schema._def } as the second parameter to all of the z.Zod<thing>.create() function calls, thus preserving not only the description but errorMap, invalid_type_error, and required_error.

I updated the code to account for all known flaws. The usage of .create() was removed to be more "extension-proof".

Aside: Because my callback fn needs to call an API to fetch the list of valid string values, I had to implement an async version of mapOnSchema.

I mean, technically might not be necessary, it can be done in three passes (since the mapping order is deterministic, unless using lazy schemas):

1. Use mapOnSchema with the identity function, but as a side-effect, push all required requests into an eg. array (as promises).
2. Await all the promises in the array, into a new resolved one.
3. Run mapOnSchema again, this time reading the resolved values from the array (with an incrementing index).

Updated the solution to with more details and a license.

@jaens Thanks for the update. Will be great if you can add JS doc comments to all exported functions to clearly differentiate their usage.

Looks time to turn this gist into a published library.