dns: Add dns/promises alias

doc/api/dns.md

@@ -611,7 +611,7 @@ earlier ones time out or result in some other error.
 
 The `dns.promises` API provides an alternative set of asynchronous DNS methods
 that return `Promise` objects rather than using callbacks. The API is accessible
-via `require('dns').promises`.
+via `require('dns').promises` or `require('dns/promises')`.
 
 ### Class: `dnsPromises.Resolver`
 <!-- YAML

lib/dns/promises.js

@@ -0,0 +1,5 @@
+'use strict';
+
+const dnsPromises = require('internal/dns/promises');
+dnsPromises.setServers = require('dns').setServers;
+module.exports = dnsPromises;

node.gyp

@@ -48,6 +48,7 @@
       'lib/cluster.js',
       'lib/dgram.js',
       'lib/dns.js',
+      'lib/dns/promises.js',
       'lib/domain.js',
       'lib/events.js',
       'lib/fs.js',

test/es-module/test-esm-dns-promises.mjs

@@ -0,0 +1,14 @@
+// Flags: --expose-internals
+import '../common/index.mjs';
+import assert from 'assert';
+import { lookupService } from 'dns/promises';
+
+const invalidAddress = 'fasdfdsaf';
+
+assert.throws(() => {
+  lookupService(invalidAddress, 0);
+}, {
+  code: 'ERR_INVALID_OPT_VALUE',
+  name: 'TypeError',
+  message: `The value "${invalidAddress}" is invalid for option "address"`
+});

test/parallel/test-dns-promises-exists.js

@@ -0,0 +1,6 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+assert.strictEqual(require('dns/promises'), require('dns').promises);

test/parallel/test-dns-setservers-type-check.js

@@ -85,3 +85,36 @@ const promiseResolver = new dns.promises.Resolver();
     );
   });
 }
+
+// This test for 'dns/promises'
+{
+  const {
+    setServers
+  } = require('dns/promises');
+
+  // This should not throw any error.
+  (async () => {
+    setServers([ '127.0.0.1' ]);
+  })();
+
+  [
+    [null],
+    [undefined],
+    [Number(addresses.DNS4_SERVER)],
+    [
+      {
+        address: addresses.DNS4_SERVER
+      }
+    ]
+  ].forEach((val) => {
+    const errObj = {
+      code: 'ERR_INVALID_ARG_TYPE',
+      name: 'TypeError',
+      message: 'The "servers[0]" argument must be of type string.' +
+              common.invalidArgTypeHelper(val[0])
+    };
+    assert.throws(() => {
+      setServers(val);
+    }, errObj);
+  });
+}