From 46a816fa00a346e7101fe4186cdccb38627d6b13 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Mon, 21 Jan 2019 20:45:55 +0100
Subject: [PATCH] events: show inspected error in uncaught 'error' message

If there is no handler for `.emit('error', value)` and `value`
is not an `Error` object, we currently just call `.toString()`
on it.

Almost always, using `util.inspect()` provides better information
for diagnostic purposes, so prefer to use that instead.

Refs: https://github.com/nodejs/help/issues/1729

PR-URL: https://github.com/nodejs/node/pull/25621
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
---
 lib/events.js                              | 11 ++++++++++-
 test/parallel/test-event-emitter-errors.js | 15 ++++++++++++++-
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/lib/events.js b/lib/events.js
index aed1ab67920560..7971a7363530c9 100644
--- a/lib/events.js
+++ b/lib/events.js
@@ -173,9 +173,18 @@ EventEmitter.prototype.emit = function emit(type, ...args) {
       // up in Node's output if this results in an unhandled exception.
       throw er; // Unhandled 'error' event
     }
+
+    let stringifiedEr;
+    const { inspect } = require('internal/util/inspect');
+    try {
+      stringifiedEr = inspect(er);
+    } catch {
+      stringifiedEr = er;
+    }
+
     // At least give some kind of context to the user
     const errors = lazyErrors();
-    const err = new errors.ERR_UNHANDLED_ERROR(er);
+    const err = new errors.ERR_UNHANDLED_ERROR(stringifiedEr);
     err.context = er;
     throw err; // Unhandled 'error' event
   }
diff --git a/test/parallel/test-event-emitter-errors.js b/test/parallel/test-event-emitter-errors.js
index ef2bbee93f8bfd..13d3a98d9c0a50 100644
--- a/test/parallel/test-event-emitter-errors.js
+++ b/test/parallel/test-event-emitter-errors.js
@@ -1,6 +1,7 @@
 'use strict';
 const common = require('../common');
 const EventEmitter = require('events');
+const util = require('util');
 
 const EE = new EventEmitter();
 
@@ -9,12 +10,24 @@ common.expectsError(
   {
     code: 'ERR_UNHANDLED_ERROR',
     type: Error,
-    message: 'Unhandled error. (Accepts a string)'
+    message: "Unhandled error. ('Accepts a string')"
   }
 );
 
 common.expectsError(
   () => EE.emit('error', { message: 'Error!' }),
+  {
+    code: 'ERR_UNHANDLED_ERROR',
+    type: Error,
+    message: "Unhandled error. ({ message: 'Error!' })"
+  }
+);
+
+common.expectsError(
+  () => EE.emit('error', {
+    message: 'Error!',
+    [util.inspect.custom]() { throw new Error(); }
+  }),
   {
     code: 'ERR_UNHANDLED_ERROR',
     type: Error,