From 08fa1f89c39bd8ef71d98b845b5bfafdb2a4595c Mon Sep 17 00:00:00 2001
From: Fraol Lemecha <fraol0912@gmail.com>
Date: Fri, 12 Sep 2025 21:36:55 +0300
Subject: [PATCH] fix: should infer types correctly when empty list of plugins
 is provided (#4612)

---
 packages/better-auth/src/db/field.ts          | 26 ++++++++++---------
 packages/better-auth/src/test-utils/index.ts  |  2 +-
 .../src/test-utils/test-instance.ts           |  2 +-
 packages/better-auth/src/types/options.ts     |  2 +-
 packages/better-auth/src/types/types.test.ts  | 22 ++++++++++++++++
 5 files changed, 39 insertions(+), 15 deletions(-)

diff --git a/packages/better-auth/src/db/field.ts b/packages/better-auth/src/db/field.ts
index 41c77abf..b66cef58 100644
--- a/packages/better-auth/src/db/field.ts
+++ b/packages/better-auth/src/db/field.ts
@@ -274,19 +274,21 @@ export type InferFieldsFromPlugins<
 	Options extends BetterAuthOptions,
 	Key extends string,
 	Format extends "output" | "input" = "output",
-> = Options["plugins"] extends Array<infer T>
-	? T extends {
-			schema: {
-				[key in Key]: {
-					fields: infer Field;
+> = Options["plugins"] extends []
+	? {}
+	: Options["plugins"] extends Array<infer T>
+		? T extends {
+				schema: {
+					[key in Key]: {
+						fields: infer Field;
+					};
 				};
-			};
-		}
-		? Format extends "output"
-			? InferFieldsOutput<Field>
-			: InferFieldsInput<Field>
-		: {}
-	: {};
+			}
+			? Format extends "output"
+				? InferFieldsOutput<Field>
+				: InferFieldsInput<Field>
+			: {}
+		: {};
 
 export type InferFieldsFromOptions<
 	Options extends BetterAuthOptions,
diff --git a/packages/better-auth/src/test-utils/index.ts b/packages/better-auth/src/test-utils/index.ts
index 2f00866c..fc81a009 100644
--- a/packages/better-auth/src/test-utils/index.ts
+++ b/packages/better-auth/src/test-utils/index.ts
@@ -93,7 +93,7 @@ export async function getTestInstanceMemory<
 			...options?.advanced,
 		},
 		plugins: [bearer(), ...(options?.plugins || [])],
-	} as O extends undefined ? typeof opts : O & typeof opts);
+	} as unknown as O extends undefined ? typeof opts : O & typeof opts);
 
 	const testUser = {
 		email: "test@test.com",
diff --git a/packages/better-auth/src/test-utils/test-instance.ts b/packages/better-auth/src/test-utils/test-instance.ts
index 07de0c25..db15c049 100644
--- a/packages/better-auth/src/test-utils/test-instance.ts
+++ b/packages/better-auth/src/test-utils/test-instance.ts
@@ -109,7 +109,7 @@ export async function getTestInstance<
 			...options?.advanced,
 		},
 		plugins: [bearer(), ...(options?.plugins || [])],
-	} as O extends undefined ? typeof opts : O & typeof opts);
+	} as unknown as O extends undefined ? typeof opts : O & typeof opts);
 
 	const testUser = {
 		email: "test@test.com",
diff --git a/packages/better-auth/src/types/options.ts b/packages/better-auth/src/types/options.ts
index b5c686b9..df01fb11 100644
--- a/packages/better-auth/src/types/options.ts
+++ b/packages/better-auth/src/types/options.ts
@@ -291,7 +291,7 @@ export type BetterAuthOptions = {
 	/**
 	 * List of Better Auth plugins
 	 */
-	plugins?: BetterAuthPlugin[];
+	plugins?: [] | BetterAuthPlugin[];
 	/**
 	 * User configuration
 	 */
diff --git a/packages/better-auth/src/types/types.test.ts b/packages/better-auth/src/types/types.test.ts
index f1c36001..4107c5c5 100644
--- a/packages/better-auth/src/types/types.test.ts
+++ b/packages/better-auth/src/types/types.test.ts
@@ -55,4 +55,26 @@ describe("general types", async (it) => {
 			activeOrganizationId?: string | undefined | null;
 		}>();
 	});
+
+	it("should infer the same types for empty plugins and no plugins", async () => {
+		const { auth: authWithEmptyPlugins } = await getTestInstance({
+			plugins: [],
+			secret: "test-secret",
+			emailAndPassword: {
+				enabled: true,
+			},
+		});
+
+		const { auth: authWithoutPlugins } = await getTestInstance({
+			secret: "test-secret",
+			emailAndPassword: {
+				enabled: true,
+			},
+		});
+
+		type SessionWithEmptyPlugins = typeof authWithEmptyPlugins.$Infer;
+		type SessionWithoutPlugins = typeof authWithoutPlugins.$Infer;
+
+		expectTypeOf<SessionWithEmptyPlugins>().toEqualTypeOf<SessionWithoutPlugins>();
+	});
 });