From b5156586ebd71d843295da130df9b849b8307088 Mon Sep 17 00:00:00 2001
From: ssi02014 <ssi02014@naver.com>
Date: Wed, 24 Sep 2025 14:23:27 +0900
Subject: [PATCH 1/2] refac(errors): Unify code structure and improve types

---
 packages/zod/src/v4/core/errors.ts | 22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/packages/zod/src/v4/core/errors.ts b/packages/zod/src/v4/core/errors.ts
index 4d8465606f..31eb3b6df4 100644
--- a/packages/zod/src/v4/core/errors.ts
+++ b/packages/zod/src/v4/core/errors.ts
@@ -226,9 +226,9 @@ type _FlattenedError<T, U = string> = {
 
 export function flattenError<T>(error: $ZodError<T>): _FlattenedError<T>;
 export function flattenError<T, U>(error: $ZodError<T>, mapper?: (issue: $ZodIssue) => U): _FlattenedError<T, U>;
-export function flattenError(error: $ZodError, mapper = (issue: $ZodIssue) => issue.message): any {
-  const fieldErrors: any = {};
-  const formErrors: any[] = [];
+export function flattenError<T, U>(error: $ZodError<T>, mapper = (issue: $ZodIssue) => issue.message as U) {
+  const fieldErrors: Record<PropertyKey, any> = {};
+  const formErrors: U[] = [];
   for (const sub of error.issues) {
     if (sub.path.length > 0) {
       fieldErrors[sub.path[0]!] = fieldErrors[sub.path[0]!] || [];
@@ -254,12 +254,7 @@ export type $ZodFormattedError<T, U = string> = {
 
 export function formatError<T>(error: $ZodError<T>): $ZodFormattedError<T>;
 export function formatError<T, U>(error: $ZodError<T>, mapper?: (issue: $ZodIssue) => U): $ZodFormattedError<T, U>;
-export function formatError<T>(error: $ZodError, _mapper?: any) {
-  const mapper: (issue: $ZodIssue) => any =
-    _mapper ||
-    function (issue: $ZodIssue) {
-      return issue.message;
-    };
+export function formatError<T, U>(error: $ZodError, mapper = (issue: $ZodIssue) => issue.message as U) {
   const fieldErrors: $ZodFormattedError<T> = { _errors: [] } as any;
   const processError = (error: { issues: $ZodIssue[] }) => {
     for (const issue of error.issues) {
@@ -307,12 +302,7 @@ export type $ZodErrorTree<T, U = string> = T extends util.Primitive
 
 export function treeifyError<T>(error: $ZodError<T>): $ZodErrorTree<T>;
 export function treeifyError<T, U>(error: $ZodError<T>, mapper?: (issue: $ZodIssue) => U): $ZodErrorTree<T, U>;
-export function treeifyError<T>(error: $ZodError, _mapper?: any) {
-  const mapper: (issue: $ZodIssue) => any =
-    _mapper ||
-    function (issue: $ZodIssue) {
-      return issue.message;
-    };
+export function treeifyError<T, U>(error: $ZodError<T>, mapper = (issue: $ZodIssue) => issue.message as U) {
   const result: $ZodErrorTree<T> = { errors: [] } as any;
   const processError = (error: { issues: $ZodIssue[] }, path: PropertyKey[] = []) => {
     for (const issue of error.issues) {
@@ -326,7 +316,7 @@ export function treeifyError<T>(error: $ZodError, _mapper?: any) {
       } else {
         const fullpath = [...path, ...issue.path];
         if (fullpath.length === 0) {
-          result.errors.push(mapper(issue));
+          result.errors.push(mapper(issue) as string);
           continue;
         }
 

From d9d3cf7bb5b1c3f537791dbd575751795473a80b Mon Sep 17 00:00:00 2001
From: ssi02014 <ssi02014@naver.com>
Date: Wed, 24 Sep 2025 14:32:41 +0900
Subject: [PATCH 2/2] refac: fixed type

---
 packages/zod/src/v4/core/errors.ts | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/zod/src/v4/core/errors.ts b/packages/zod/src/v4/core/errors.ts
index 31eb3b6df4..29c247b516 100644
--- a/packages/zod/src/v4/core/errors.ts
+++ b/packages/zod/src/v4/core/errors.ts
@@ -254,7 +254,7 @@ export type $ZodFormattedError<T, U = string> = {
 
 export function formatError<T>(error: $ZodError<T>): $ZodFormattedError<T>;
 export function formatError<T, U>(error: $ZodError<T>, mapper?: (issue: $ZodIssue) => U): $ZodFormattedError<T, U>;
-export function formatError<T, U>(error: $ZodError, mapper = (issue: $ZodIssue) => issue.message as U) {
+export function formatError<T, U>(error: $ZodError<T>, mapper = (issue: $ZodIssue) => issue.message as U) {
   const fieldErrors: $ZodFormattedError<T> = { _errors: [] } as any;
   const processError = (error: { issues: $ZodIssue[] }) => {
     for (const issue of error.issues) {
@@ -303,7 +303,7 @@ export type $ZodErrorTree<T, U = string> = T extends util.Primitive
 export function treeifyError<T>(error: $ZodError<T>): $ZodErrorTree<T>;
 export function treeifyError<T, U>(error: $ZodError<T>, mapper?: (issue: $ZodIssue) => U): $ZodErrorTree<T, U>;
 export function treeifyError<T, U>(error: $ZodError<T>, mapper = (issue: $ZodIssue) => issue.message as U) {
-  const result: $ZodErrorTree<T> = { errors: [] } as any;
+  const result: $ZodErrorTree<T, U> = { errors: [] } as any;
   const processError = (error: { issues: $ZodIssue[] }, path: PropertyKey[] = []) => {
     for (const issue of error.issues) {
       if (issue.code === "invalid_union" && issue.errors.length) {
@@ -316,7 +316,7 @@ export function treeifyError<T, U>(error: $ZodError<T>, mapper = (issue: $ZodIss
       } else {
         const fullpath = [...path, ...issue.path];
         if (fullpath.length === 0) {
-          result.errors.push(mapper(issue) as string);
+          result.errors.push(mapper(issue));
           continue;
         }