fix: should infer types correctly when empty list of plugins is provided (#4612)

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,

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",

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",

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
 	 */

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>();
+	});
 });