From 7802d7811b77210c628e91f3a8778df208e4933a Mon Sep 17 00:00:00 2001
From: Jon Koops <jonkoops@gmail.com>
Date: Thu, 6 Mar 2025 16:13:55 +0100
Subject: [PATCH] feat: deprecate non-native Promises

Signed-off-by: Jon Koops <jonkoops@gmail.com>
---
 index.js     | 5 +++++
 lib/layer.js | 9 +++++++++
 package.json | 1 +
 3 files changed, 15 insertions(+)

diff --git a/index.js b/index.js
index 5c5caa2..4358aeb 100644
--- a/index.js
+++ b/index.js
@@ -18,6 +18,7 @@ const { METHODS } = require('node:http')
 const parseUrl = require('parseurl')
 const Route = require('./lib/route')
 const debug = require('debug')('router')
+const deprecate = require('depd')('router')
 
 /**
  * Module variables.
@@ -647,6 +648,10 @@ function processParams (params, layer, called, req, res, done) {
     try {
       const ret = fn(req, res, paramCallback, paramVal, key)
       if (isPromise(ret)) {
+        if (!(ret instanceof Promise)) {
+          deprecate('parameters that are Promise-like are deprecated, use a native Promise instead')
+        }
+
         ret.then(null, function (error) {
           paramCallback(error || new Error('Rejected promise'))
         })
diff --git a/lib/layer.js b/lib/layer.js
index d228617..6a4408f 100644
--- a/lib/layer.js
+++ b/lib/layer.js
@@ -15,6 +15,7 @@
 const isPromise = require('is-promise')
 const pathRegexp = require('path-to-regexp')
 const debug = require('debug')('router:layer')
+const deprecate = require('depd')('router')
 
 /**
  * Module variables.
@@ -116,6 +117,10 @@ Layer.prototype.handleError = function handleError (error, req, res, next) {
 
     // wait for returned promise
     if (isPromise(ret)) {
+      if (!(ret instanceof Promise)) {
+        deprecate('handlers that are Promise-like are deprecated, use a native Promise instead')
+      }
+
       ret.then(null, function (error) {
         next(error || new Error('Rejected promise'))
       })
@@ -148,6 +153,10 @@ Layer.prototype.handleRequest = function handleRequest (req, res, next) {
 
     // wait for returned promise
     if (isPromise(ret)) {
+      if (!(ret instanceof Promise)) {
+        deprecate('handlers that are Promise-like are deprecated, use a native Promise instead')
+      }
+
       ret.then(null, function (error) {
         next(error || new Error('Rejected promise'))
       })
diff --git a/package.json b/package.json
index d819cd3..b5493d2 100644
--- a/package.json
+++ b/package.json
@@ -10,6 +10,7 @@
   "repository": "pillarjs/router",
   "dependencies": {
     "debug": "^4.4.0",
+    "depd": "^2.0.0",
     "is-promise": "^4.0.0",
     "parseurl": "^1.3.3",
     "path-to-regexp": "^8.0.0"