Zod 4 adapter now respects global customError configuration when no explicit error map is provided.

Author: ciscoheat

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Zod 4 adapter: Allow top-level `.transform()` and `.refine()` in schemas. [#646](https://github.com/ciscoheat/sveltekit-superforms/issues/646).
+- Zod 4 adapter: Now respects global `customError` configuration when no explicit error map is provided. The adapter prioritizes `customError` over `localeError`. [#618](https://github.com/ciscoheat/sveltekit-superforms/issues/618).
 
 ## [2.28.0] - 2025-10-19
 

src/lib/adapters/zod4.ts

@@ -130,7 +130,11 @@ async function validate<T extends ZodValidationSchema>(
 	error: $ZodErrorMap | undefined
 ): Promise<ValidationResult<Infer<T, 'zod4'>>> {
 	// Use Zod's global config error map if none provided to preserve custom messages.
-	if (error === undefined) error = config().localeError;
+	// Prioritize customError over localeError when both are set.
+	if (error === undefined) {
+		const zConfig = config();
+		error = zConfig.customError ?? zConfig.localeError;
+	}
 	const result = await safeParseAsync(schema, data, { error });
 	if (result.success) {
 		return {

src/tests/issue-639.test.ts

@@ -79,4 +79,25 @@ describe('Issue #639 - Zod v4 generic error messages in dev mode', () => {
 			expect(error.toLowerCase()).not.toBe('invalid input');
 		}
 	});
+
+	test('Global custom error respected', async () => {
+		z.config({
+			customError: () => 'Global error'
+		});
+		// Schema with explicit custom error messages
+		const customSchema = z.object({
+			username: z.string().min(3)
+		});
+
+		const formData = new FormData();
+		formData.set('username', 'ab'); // Too short
+
+		const form = await superValidate(formData, zod(customSchema));
+		expect(form.valid).toBe(false);
+
+		const usernameErrors = form.errors.username ?? [];
+
+		// Verify custom messages are present
+		expect(usernameErrors).toContain('Global error');
+	});
 });