From 5a96702a5bc06bd17866815b6664293eade51225 Mon Sep 17 00:00:00 2001
From: ExE Boss <3889017+ExE-Boss@users.noreply.github.com>
Date: Fri, 7 Feb 2020 11:40:00 +0100
Subject: [PATCH 1/3] =?UTF-8?q?util:=20Use=C2=A0a=C2=A0global=C2=A0symbol?=
 =?UTF-8?q?=20for=C2=A0`util.promisify.custom`?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Define `util.promisify.custom`
as `Symbol.for("nodejs.util.inspect.custom")`, rather than
as `Symbol("util.inspect.custom")`.

This allows custom `promisify` wrappers to easily/safely be defined
in non‑Node.js environments.

Fixes: https://github.com/nodejs/node/issues/31647
---
 lib/internal/util.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/internal/util.js b/lib/internal/util.js
index 5eb5ba9e966ff9..f26ea970e8dce0 100644
--- a/lib/internal/util.js
+++ b/lib/internal/util.js
@@ -271,7 +271,7 @@ function getSystemErrorName(err) {
   return entry ? entry[0] : `Unknown system error ${err}`;
 }
 
-const kCustomPromisifiedSymbol = Symbol('util.promisify.custom');
+const kCustomPromisifiedSymbol = SymbolFor('nodejs.util.promisify.custom');
 const kCustomPromisifyArgsSymbol = Symbol('customPromisifyArgs');
 
 function promisify(original) {

From 17982663cb7c8069e77b0ac65f331aec8d9fe3d3 Mon Sep 17 00:00:00 2001
From: ExE Boss <3889017+ExE-Boss@users.noreply.github.com>
Date: Fri, 7 Feb 2020 12:00:00 +0100
Subject: [PATCH 2/3] =?UTF-8?q?docs(util):=20Use=C2=A0a=C2=A0global=C2=A0s?=
 =?UTF-8?q?ymbol=20for=C2=A0`util.promisify.custom`?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 doc/api/util.md | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/doc/api/util.md b/doc/api/util.md
index 9f48a5b8fd72e0..5585279d2bb45c 100644
--- a/doc/api/util.md
+++ b/doc/api/util.md
@@ -995,11 +995,32 @@ throw an error.
 ### `util.promisify.custom`
 <!-- YAML
 added: v8.0.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/31672
+    description: This is now defined as a shared symbol.
 -->
 
 * {symbol} that can be used to declare custom promisified variants of functions,
 see [Custom promisified functions][].
 
+In addition to being accessible through `util.promisify.custom`, this
+symbol is [registered globally][global symbol registry] and can be
+accessed in any environment as `Symbol.for('nodejs.util.promisify.custom')`.
+
+For example, with a function that takes in
+`(foo, onSuccessCallback, onErrorCallback)`:
+
+```js
+const kCustomPromisifiedSymbol = Symbol.for('nodejs.util.promisify.custom');
+
+doSomething[kCustomPromisifiedSymbol] = (foo) => {
+  return new Promise((resolve, reject) => {
+    doSomething(foo, resolve, reject);
+  });
+};
+```
+
 ## Class: `util.TextDecoder`
 <!-- YAML
 added: v8.3.0

From e7d919e3e436fc8f37e4b36d849932e271ee0e30 Mon Sep 17 00:00:00 2001
From: ExE Boss <3889017+ExE-Boss@users.noreply.github.com>
Date: Fri, 7 Feb 2020 12:20:00 +0100
Subject: [PATCH 3/3] =?UTF-8?q?test(util):=20Use=C2=A0a=C2=A0global=C2=A0s?=
 =?UTF-8?q?ymbol=20for=C2=A0`util.promisify.custom`?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 test/parallel/test-util-promisify.js | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/test/parallel/test-util-promisify.js b/test/parallel/test-util-promisify.js
index 4ed1653984762c..c18f454d2f77ef 100644
--- a/test/parallel/test-util-promisify.js
+++ b/test/parallel/test-util-promisify.js
@@ -33,6 +33,21 @@ const stat = promisify(fs.stat);
   assert.strictEqual(promisify(promisify(fn)), promisifedFn);
 }
 
+{
+  function fn() {}
+
+  function promisifiedFn() {}
+
+  // util.promisify.custom is a shared symbol which can be accessed
+  // as `Symbol.for("nodejs.util.promisify.custom")`.
+  const kCustomPromisifiedSymbol = Symbol.for('nodejs.util.promisify.custom');
+  fn[kCustomPromisifiedSymbol] = promisifiedFn;
+
+  assert.strictEqual(kCustomPromisifiedSymbol, promisify.custom);
+  assert.strictEqual(promisify(fn), promisifiedFn);
+  assert.strictEqual(promisify(promisify(fn)), promisifiedFn);
+}
+
 {
   function fn() {}
   fn[promisify.custom] = 42;