fix(db): use static zod lookup in toZodSchema so locales tree-shake (#10866)

Co-authored-by: Taesu <166604494+bytaesu@users.noreply.github.com>
Co-authored-by: Taesu <bytaesu@gmail.com>

.changeset/organization-zod-locales.md

@@ -0,0 +1,5 @@
+---
+"better-auth": patch
+---
+
+The organization plugin no longer pulls every zod locale into server bundles.

e2e/smoke/test/esbuild.spec.ts

@@ -68,6 +68,51 @@ it("build minimal without unexpected imports", async () => {
 	);
 });
 
+/**
+ * @see https://github.com/better-auth/better-auth/issues/10865
+ */
+it("build organization plugin without unused zod locales", async () => {
+	const esbuildDir = join(fixturesDir, "esbuild");
+	const buildProcess = spawn(
+		"pnpm",
+		[
+			"exec",
+			"esbuild",
+			"src/organization.ts",
+			"--bundle",
+			"--outfile=dist/organization.js",
+		],
+		{
+			cwd: esbuildDir,
+			stdio: ["ignore", "inherit", "inherit"],
+		},
+	);
+	await new Promise<void>((resolve, reject) => {
+		buildProcess.once("error", reject);
+		buildProcess.once("close", (code) => {
+			if (code === 0) {
+				resolve();
+			} else {
+				reject(
+					new Error(`esbuild organization build failed with code ${code}`),
+				);
+			}
+		});
+	});
+	const outputFile = join(esbuildDir, "dist", "organization.js");
+	const outputContent = await readFile(outputFile, "utf-8");
+	const locales = outputContent.match(/zod\/v4\/locales\/[\w-]+\.js/g) ?? [];
+	const unusedLocales = locales.filter(
+		(locale) =>
+			locale !== "zod/v4/locales/en.js" && locale !== "zod/v4/locales/index.js",
+	);
+	assert.deepStrictEqual(
+		unusedLocales,
+		[],
+		"Built output should not contain unused zod locales",
+	);
+});
+
 /**
  * @see https://github.com/better-auth/better-auth/issues/10366
  */

e2e/smoke/test/fixtures/esbuild/src/organization.ts

@@ -0,0 +1,4 @@
+import { betterAuth } from "better-auth/minimal";
+import { organization } from "better-auth/plugins";
+
+export const auth = betterAuth({ plugins: [organization()] });

packages/better-auth/src/db/to-zod.test.ts

@@ -33,6 +33,24 @@ describe("toZodSchema", () => {
 		});
 	});
 
+	describe("scalar field types", () => {
+		it("should map each scalar type to its zod schema", () => {
+			const schema = toZodSchema({
+				fields: {
+					name: { type: "string" },
+					age: { type: "number" },
+					active: { type: "boolean" },
+					createdAt: { type: "date" },
+				},
+				isClientSide: true,
+			});
+
+			const valid = { name: "a", age: 1, active: true, createdAt: new Date() };
+			expect(schema.parse(valid)).toEqual(valid);
+			expect(schema.safeParse({ ...valid, age: "1" }).success).toBe(false);
+		});
+	});
+
 	describe("required: false field nullability", () => {
 		it("should accept null, undefined, and a value for an optional field", () => {
 			const schema = toZodSchema({

packages/better-auth/src/db/to-zod.ts

@@ -2,6 +2,17 @@ import type { DBFieldAttribute } from "@better-auth/core/db";
 import type { ZodType } from "zod";
 import * as z from "zod";
 
+/**
+ * Static lookup keeps `zod` tree-shakeable. `z[field.type]()` forces bundlers
+ * to retain every `zod` export, including all locales.
+ */
+const scalarSchemas = {
+	string: z.string,
+	number: z.number,
+	boolean: z.boolean,
+	date: z.date,
+};
+
 export function toZodSchema<
 	Fields extends Record<string, DBFieldAttribute | never>,
 	IsClientSide extends boolean,
@@ -32,7 +43,7 @@ export function toZodSchema<
 		} else if (Array.isArray(field.type)) {
 			schema = z.any();
 		} else {
-			schema = z[field.type]();
+			schema = scalarSchemas[field.type]();
 		}
 
 		if (field?.required === false) {