fix(types): prevent any from collapsing base type and client inference (#8981)

.changeset/violet-papayas-see.md

@@ -0,0 +1,5 @@
+---
+"better-auth": patch
+---
+
+Prevent `any` from collapsing `auth.$Infer` and `auth.$ERROR_CODES`. Preserve client query typing when body is `any`.

packages/better-auth/src/client/path-to-object.ts

@@ -6,6 +6,7 @@ import type { BetterFetchResponse } from "@better-fetch/fetch";
 import type { Endpoint, InputContext, StandardSchemaV1 } from "better-call";
 import type {
 	HasRequiredKeys,
+	IsAny,
 	Prettify,
 	UnionToIntersection,
 } from "../types/helper";
@@ -108,30 +109,35 @@ export type InferUserUpdateCtx<
 	UnionToIntersection<InferAdditionalFromClient<ClientOpts, "user", "input">>
 >;
 
+type InferCtxQuery<
+	C extends InputContext<any, any>,
+	FetchOptions extends ClientFetchOption,
+> =
+	C["query"] extends Record<string, any>
+		? {
+				query: C["query"];
+				fetchOptions?: FetchOptions | undefined;
+			}
+		: C["query"] extends Record<string, any> | undefined
+			? {
+					query?: C["query"] | undefined;
+					fetchOptions?: FetchOptions | undefined;
+				}
+			: {
+					fetchOptions?: FetchOptions | undefined;
+				};
+
 export type InferCtx<
 	C extends InputContext<any, any>,
 	FetchOptions extends ClientFetchOption,
-> = 0 extends 1 & C["body"]
-	? {
-			fetchOptions?: FetchOptions | undefined;
-		}
-	: C["body"] extends Record<string, any>
-		? C["body"] & {
-				fetchOptions?: FetchOptions | undefined;
-			}
-		: C["query"] extends Record<string, any>
-			? {
-					query: C["query"];
+> =
+	IsAny<C["body"]> extends true
+		? InferCtxQuery<C, FetchOptions>
+		: C["body"] extends Record<string, any>
+			? C["body"] & {
 					fetchOptions?: FetchOptions | undefined;
 				}
-			: C["query"] extends Record<string, any> | undefined
-				? {
-						query?: C["query"] | undefined;
-						fetchOptions?: FetchOptions | undefined;
-					}
-				: {
-						fetchOptions?: FetchOptions | undefined;
-					};
+			: InferCtxQuery<C, FetchOptions>;
 
 export type MergeRoutes<T> = UnionToIntersection<T>;
 

packages/better-auth/src/types/helper.ts

@@ -1,3 +1,5 @@
+export type IsAny<T> = 0 extends 1 & T ? true : false;
+
 export type Prettify<T> = Omit<T, never>;
 
 export type PrettifyDeep<T> = {
@@ -29,12 +31,41 @@ export type RequiredKeysOf<BaseType extends object> = Exclude<
 	undefined
 >;
 
-export type HasRequiredKeys<BaseType> = 0 extends 1 & BaseType
-	? false
-	: [BaseType] extends [object]
-		? RequiredKeysOf<BaseType & object> extends never
-			? false
-			: true
-		: false;
+export type HasRequiredKeys<BaseType> =
+	IsAny<BaseType> extends true
+		? false
+		: [BaseType] extends [object]
+			? RequiredKeysOf<BaseType & object> extends never
+				? false
+				: true
+			: false;
 
 export type StripEmptyObjects<T extends object> = { [K in keyof T]: T[K] };
+
+/**
+ * Extracts a Record-typed field from a plugin, guarding against `any`.
+ */
+export type ExtractPluginField<T, Field extends string> =
+	IsAny<T> extends true
+		? {}
+		: T extends { [K in Field]?: Record<string, any> }
+			? T[Field] extends Record<string, any>
+				? T[Field]
+				: {}
+			: {};
+
+/**
+ * Walks a plugin tuple with tail-recursive accumulator (TS 4.5+),
+ * extracting and intersecting the given field from each element.
+ */
+export type InferPluginFieldFromTuple<
+	T extends readonly unknown[],
+	Field extends string,
+	Acc = {},
+> = T extends readonly [infer Head, ...infer Tail]
+	? InferPluginFieldFromTuple<
+			Tail,
+			Field,
+			Acc & ExtractPluginField<Head, Field>
+		>
+	: Acc;

packages/better-auth/src/types/models.ts

@@ -1,9 +1,13 @@
-import type { BetterAuthOptions, BetterAuthPlugin } from "@better-auth/core";
+import type { BetterAuthOptions } from "@better-auth/core";
 import type {
 	InferDBFieldsFromOptionsInput,
 	InferDBFieldsFromPluginsInput,
 } from "@better-auth/core/db";
-import type { UnionToIntersection } from "./helper";
+import type {
+	ExtractPluginField,
+	InferPluginFieldFromTuple,
+	UnionToIntersection,
+} from "./helper";
 
 export type AdditionalUserFieldsInput<Options extends BetterAuthOptions> =
 	InferDBFieldsFromPluginsInput<"user", Options["plugins"]> &
@@ -14,15 +18,11 @@ export type AdditionalSessionFieldsInput<Options extends BetterAuthOptions> =
 		InferDBFieldsFromOptionsInput<Options["session"]>;
 
 export type InferPluginTypes<O extends BetterAuthOptions> =
-	O["plugins"] extends Array<infer P>
-		? UnionToIntersection<
-				P extends BetterAuthPlugin
-					? P["$Infer"] extends Record<string, any>
-						? P["$Infer"]
-						: {}
-					: {}
-			>
-		: {};
+	O["plugins"] extends readonly [unknown, ...unknown[]]
+		? InferPluginFieldFromTuple<O["plugins"], "$Infer">
+		: O["plugins"] extends Array<infer P>
+			? UnionToIntersection<ExtractPluginField<P, "$Infer">>
+			: {};
 
 export type {
 	Account,

packages/better-auth/src/types/plugins.ts

@@ -5,7 +5,11 @@ import type {
 } from "@better-auth/core";
 
 import type { BetterAuthPluginDBSchema } from "@better-auth/core/db";
-import type { UnionToIntersection } from "./helper";
+import type {
+	ExtractPluginField,
+	InferPluginFieldFromTuple,
+	UnionToIntersection,
+} from "./helper";
 
 export type InferOptionSchema<S extends BetterAuthPluginDBSchema> =
 	S extends Record<string, { fields: infer Fields }>
@@ -22,15 +26,11 @@ export type InferOptionSchema<S extends BetterAuthPluginDBSchema> =
 		: never;
 
 export type InferPluginErrorCodes<O extends BetterAuthOptions> =
-	O["plugins"] extends Array<infer P>
-		? UnionToIntersection<
-				P extends BetterAuthPlugin
-					? P["$ERROR_CODES"] extends Record<string, any>
-						? P["$ERROR_CODES"]
-						: {}
-					: {}
-			>
-		: {};
+	O["plugins"] extends readonly [unknown, ...unknown[]]
+		? InferPluginFieldFromTuple<O["plugins"], "$ERROR_CODES">
+		: O["plugins"] extends Array<infer P>
+			? UnionToIntersection<ExtractPluginField<P, "$ERROR_CODES">>
+			: {};
 
 export type InferPluginIDs<O extends BetterAuthOptions> =
 	O["plugins"] extends Array<infer P>

packages/better-auth/src/types/types.test.ts

@@ -1,5 +1,4 @@
 import type { BetterAuthPlugin } from "@better-auth/core";
-import type { InputContext } from "better-call";
 import { describe, expect, expectTypeOf, it } from "vitest";
 import { createAuthEndpoint } from "../api";
 import type { InferCtx } from "../client/path-to-object";
@@ -241,10 +240,44 @@ describe("HasRequiredKeys", () => {
 	});
 });
 
-describe("InferCtx", () => {
-	it("should preserve fetchOptions when body is any", () => {
-		type Result = InferCtx<InputContext<any, any> & { body: any }, {}>;
-		type Keys = keyof Result;
-		expectTypeOf<Keys>().toEqualTypeOf<"fetchOptions">();
+describe("any-poisoning guards", () => {
+	/**
+	 * InferCtx: when body is `any`, query typing should be preserved
+	 * via InferCtxQuery delegation instead of collapsing to `any`.
+	 */
+	it("InferCtx should preserve query when body is any", () => {
+		type Result = InferCtx<
+			{ body: any; query: { page: number }; method: "GET" },
+			{}
+		>;
+		expectTypeOf<Result["query"]>().toEqualTypeOf<{ page: number }>();
+	});
+
+	/**
+	 * InferPluginTypes: an untyped plugin (`{} as any`) in the plugins array
+	 * should not collapse auth.$Infer to `any`.
+	 */
+	it("auth.$Infer should not collapse with untyped plugin", async () => {
+		const untypedPlugin = {} as any;
+		const { auth } = await getTestInstance({
+			plugins: [organization(), untypedPlugin],
+		});
+		type Infer = typeof auth.$Infer;
+		expectTypeOf<Infer>().not.toBeAny();
+		expectTypeOf<Infer>().toHaveProperty("Session");
+	});
+
+	/**
+	 * InferPluginErrorCodes: same guard as InferPluginTypes,
+	 * auth.$ERROR_CODES should not collapse to `any`.
+	 */
+	it("auth.$ERROR_CODES should not collapse with untyped plugin", async () => {
+		const untypedPlugin = {} as any;
+		const { auth } = await getTestInstance({
+			plugins: [organization(), untypedPlugin],
+		});
+		type Codes = (typeof auth)["$ERROR_CODES"];
+		expectTypeOf<Codes>().not.toBeAny();
+		expectTypeOf<Codes>().toHaveProperty("SESSION_EXPIRED");
 	});
 });