Tmp: testing with supported Promise using augmentation.

src/express5.d.ts

@@ -0,0 +1,42 @@
+/**
+ * @fileOverview Temporary adjustment to the Express 5 type declarations
+ * @see https://github.com/DefinitelyTyped/DefinitelyTyped/pull/69846/files#diff-5962769e8693df44c9e1083881fb1da149a67262026db939b7430536d514e7af
+ * */
+/* eslint-disable allowed/dependencies -- this is DTS */
+/* eslint-disable @typescript-eslint/no-explicit-any -- copying as is */
+import { ParsedQs } from "qs";
+import {
+  NextFunction,
+  ParamsDictionary,
+  Request,
+  Response,
+} from "express-serve-static-core";
+
+declare module "express-serve-static-core" {
+  export interface RequestHandler<
+    P = ParamsDictionary,
+    ResBody = any,
+    ReqBody = any,
+    ReqQuery = ParsedQs,
+    LocalsObj extends Record<string, any> = Record<string, any>,
+  > {
+    (
+      req: Request<P, ResBody, ReqBody, ReqQuery, LocalsObj>,
+      res: Response<ResBody, LocalsObj>,
+      next: NextFunction,
+    ): void | Promise<void>;
+  }
+
+  export type ErrorRequestHandler<
+    P = ParamsDictionary,
+    ResBody = any,
+    ReqBody = any,
+    ReqQuery = ParsedQs,
+    LocalsObj extends Record<string, any> = Record<string, any>,
+  > = (
+    err: any,
+    req: Request<P, ResBody, ReqBody, ReqQuery, LocalsObj>,
+    res: Response<ResBody, LocalsObj>,
+    next: NextFunction,
+  ) => void | Promise<void>;
+}