util: improve inspect for AsyncFunction

Use the constructor name in the output, if present.
This is a backport of #11210 without
the semver-major change to GeneratorFunction output.

PR-URL: #11211
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>

lib/util.js

@@ -400,11 +400,15 @@ function formatValue(ctx, value, recurseTimes) {
     });
   }
 
+  var constructor = getConstructorOf(value);
+
   // Some type of object without properties can be shortcutted.
   if (keys.length === 0) {
     if (typeof value === 'function') {
-      return ctx.stylize(`[Function${value.name ? `: ${value.name}` : ''}]`,
-                         'special');
+      const ctorName = (constructor && constructor.name === 'AsyncFunction') ?
+          'AsyncFunction' : 'Function';
+      return ctx.stylize(
+          `[${ctorName}${value.name ? `: ${value.name}` : ''}]`, 'special');
     }
     if (isRegExp(value)) {
       return ctx.stylize(RegExp.prototype.toString.call(value), 'regexp');
@@ -440,12 +444,11 @@ function formatValue(ctx, value, recurseTimes) {
     // Can't do the same for DataView because it has a non-primitive
     // .buffer property that we need to recurse for.
     if (binding.isArrayBuffer(value) || binding.isSharedArrayBuffer(value)) {
-      return `${getConstructorOf(value).name}` +
+      return `${constructor.name}` +
              ` { byteLength: ${formatNumber(ctx, value.byteLength)} }`;
     }
   }
 
-  var constructor = getConstructorOf(value);
   var base = '', empty = false, braces;
   var formatter = formatObject;
 
@@ -536,7 +539,9 @@ function formatValue(ctx, value, recurseTimes) {
 
   // Make functions say that they are functions
   if (typeof value === 'function') {
-    base = ` [Function${value.name ? `: ${value.name}` : ''}]`;
+    const ctorName = (constructor && constructor.name === 'AsyncFunction') ?
+        'AsyncFunction' : 'Function';
+    base = ` [${ctorName}${value.name ? `: ${value.name}` : ''}]`;
   }
 
   // Make RegExps say that they are RegExps

test/parallel/test-util-inspect.js

@@ -9,6 +9,8 @@ assert.strictEqual(util.inspect(false), 'false');
 assert.strictEqual(util.inspect(''), "''");
 assert.strictEqual(util.inspect('hello'), "'hello'");
 assert.strictEqual(util.inspect(function() {}), '[Function]');
+assert.strictEqual(util.inspect(async function() {}), '[AsyncFunction]');
+assert.strictEqual(util.inspect(function*() {}), '[Function]');
 assert.strictEqual(util.inspect(undefined), 'undefined');
 assert.strictEqual(util.inspect(null), 'null');
 assert.strictEqual(util.inspect(/foo(bar\n)?/gi), '/foo(bar\\n)?/gi');
@@ -28,6 +30,10 @@ assert.strictEqual(util.inspect([1, [2, 3]]), '[ 1, [ 2, 3 ] ]');
 assert.strictEqual(util.inspect({}), '{}');
 assert.strictEqual(util.inspect({a: 1}), '{ a: 1 }');
 assert.strictEqual(util.inspect({a: function() {}}), '{ a: [Function: a] }');
+assert.strictEqual(util.inspect({a: async function() {}}),
+                   '{ a: [AsyncFunction: a] }');
+assert.strictEqual(util.inspect({a: function*() {}}),
+                   '{ a: [Function: a] }');
 assert.strictEqual(util.inspect({a: 1, b: 2}), '{ a: 1, b: 2 }');
 assert.strictEqual(util.inspect({'a': {}}), '{ a: {} }');
 assert.strictEqual(util.inspect({'a': {'b': 2}}), '{ a: { b: 2 } }');