util: fix inspecting symbol key in string

PR-URL: https://github.com/nodejs/node/pull/11672
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

lib/util.js

@@ -361,6 +361,10 @@ function formatValue(ctx, value, recurseTimes) {
     // for boxed Strings, we have to remove the 0-n indexed entries,
     // since they just noisy up the output and are redundant
     keys = keys.filter(function(key) {
+      if (typeof key === 'symbol') {
+        return true;
+      }
+
       return !(key >= 0 && key < raw.length);
     });
   }

test/parallel/test-util-inspect.js

@@ -50,6 +50,9 @@ assert.strictEqual(util.inspect(Object.create({},
   {visible: {value: 1, enumerable: true}, hidden: {value: 2}})),
                    '{ visible: 1 }'
 );
+assert.strictEqual(util.inspect(Object.assign(new String('hello'),
+                   { [Symbol('foo')]: 123 }), { showHidden: true }),
+                   '{ [String: \'hello\'] [length]: 5, [Symbol(foo)]: 123 }');
 
 {
   const regexp = /regexp/;