events,test: fix TypeError in EventEmitter warning

Allows Symbol to be converted to String so it can be included in the
error.
Conflicts:
lib/events.js
Fixes: #9003
Backport-PR-URL: #12459
PR-URL: #9021
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

Author: jseagull

lib/events.js

@@ -257,8 +257,9 @@ function _addListener(target, type, listener, prepend) {
 if(m&&m>0&&existing.length>m){
 existing.warned=true;
 constw=newError('Possible EventEmitter memory leak detected. '+
-`${existing.length}${type} listeners added. `+
-'Use emitter.setMaxListeners() to increase limit');
+`${existing.length}${String(type)} listeners `+
+'added. Use emitter.setMaxListeners() to '+
+'increase limit');
 w.name='Warning';
 w.emitter=target;
 w.type=type;

test/parallel/test-event-emitter-check-listener-leaks.js

@@ -13,6 +13,14 @@ assert.ok(!e._events['default'].hasOwnProperty('warned'));
 e.on('default',function(){});
 assert.ok(e._events['default'].warned);
 
+// symbol
+constsymbol=Symbol('symbol');
+e.setMaxListeners(1);
+e.on(symbol,function(){});
+assert.ok(!e._events[symbol].hasOwnProperty('warned'));
+e.on(symbol,function(){});
+assert.ok(e._events[symbol].hasOwnProperty('warned'));
+
 // specific
 e.setMaxListeners(5);
 for(leti=0;i<5;i++){

test/parallel/test-event-emitter-max-listeners-warning-for-null.js

@@ -0,0 +1,22 @@
+// Flags: --no-warnings
+// The flag suppresses stderr output but the warning event will still emit
+'use strict';
+
+constcommon=require('../common');
+constevents=require('events');
+constassert=require('assert');
+
+conste=newevents.EventEmitter();
+e.setMaxListeners(1);
+
+process.on('warning',common.mustCall((warning)=>{
+assert.ok(warninginstanceofError);
+assert.strictEqual(warning.name,'Warning');
+assert.strictEqual(warning.emitter,e);
+assert.strictEqual(warning.count,2);
+assert.strictEqual(warning.type,null);
+assert.ok(warning.message.includes('2 null listeners added.'));
+}));
+
+e.on(null,function(){});
+e.on(null,function(){});

test/parallel/test-event-emitter-max-listeners-warning-for-symbol.js

@@ -0,0 +1,24 @@
+// Flags: --no-warnings
+// The flag suppresses stderr output but the warning event will still emit
+'use strict';
+
+constcommon=require('../common');
+constevents=require('events');
+constassert=require('assert');
+
+constsymbol=Symbol('symbol');
+
+conste=newevents.EventEmitter();
+e.setMaxListeners(1);
+
+process.on('warning',common.mustCall((warning)=>{
+assert.ok(warninginstanceofError);
+assert.strictEqual(warning.name,'Warning');
+assert.strictEqual(warning.emitter,e);
+assert.strictEqual(warning.count,2);
+assert.strictEqual(warning.type,symbol);
+assert.ok(warning.message.includes('2 Symbol(symbol) listeners added.'));
+}));
+
+e.on(symbol,function(){});
+e.on(symbol,function(){});

test/parallel/test-event-emitter-max-listeners-warning.js

@@ -15,6 +15,7 @@ process.on('warning', common.mustCall((warning) => {
 assert.strictEqual(warning.emitter,e);
 assert.strictEqual(warning.count,2);
 assert.strictEqual(warning.type,'event-type');
+assert.ok(warning.message.includes('2 event-type listeners added.'));
 }));
 
 e.on('event-type',function(){});