util: preserve length of deprecated functions

PR-URL: https://github.com/nodejs/node/pull/57806
Reviewed-By: Jordan Harband <ljharb@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>

lib/internal/util.js

@@ -142,6 +142,12 @@ function pendingDeprecate(fn, msg, code) {
     emitDeprecationWarning();
     return ReflectApply(fn, this, args);
   }
+
+  ObjectDefineProperty(deprecated, 'length', {
+    __proto__: null,
+    ...ObjectGetOwnPropertyDescriptor(fn, 'length'),
+  });
+
   return deprecated;
 }
 
@@ -180,6 +186,11 @@ function deprecate(fn, msg, code, useEmitSync) {
     deprecated.prototype = fn.prototype;
   }
 
+  ObjectDefineProperty(deprecated, 'length', {
+    __proto__: null,
+    ...ObjectGetOwnPropertyDescriptor(fn, 'length'),
+  });
+
   return deprecated;
 }
 

test/parallel/test-util-deprecate.js

@@ -1,3 +1,4 @@
+// Flags: --expose-internals
 'use strict';
 
 require('../common');
@@ -6,9 +7,27 @@ require('../common');
 
 const assert = require('assert');
 const util = require('util');
+const internalUtil = require('internal/util');
 
 const expectedWarnings = new Map();
 
+// Deprecated function length is preserved
+for (const fn of [
+  function() {},
+  function(a) {},
+  function(a, b, c) {},
+  function(...args) {},
+  function(a, b, c, ...args) {},
+  () => {},
+  (a) => {},
+  (a, b, c) => {},
+  (...args) => {},
+  (a, b, c, ...args) => {},
+]) {
+  assert.strictEqual(util.deprecate(fn).length, fn.length);
+  assert.strictEqual(internalUtil.pendingDeprecate(fn).length, fn.length);
+}
+
 // Emits deprecation only once if same function is called.
 {
   const msg = 'fhqwhgads';