feat: find free port if port is not specified

Author: ylemkimon

lib/Server.js

@@ -30,6 +30,7 @@ const getCompilerConfigArray = require('./utils/getCompilerConfigArray');
 const getStatsOption = require('./utils/getStatsOption');
 const getColorsOption = require('./utils/getColorsOption');
 const setupExitSignals = require('./utils/setupExitSignals');
+const findPort = require('./utils/findPort');
 const schema = require('./options.json');
 
 if (!process.env.WEBPACK_DEV_SERVER) {
@@ -598,26 +599,44 @@ class Server {
 
   listen(port, hostname, fn) {
     this.hostname = hostname;
+    if (typeof port !== 'undefined' && port !== this.options.port) {
+      this.logger.warn(
+        'The port specified in options and the port passed as an argument is different.'
+      );
+    }
 
-    return this.listeningApp.listen(port, hostname, (err) => {
-      if (this.options.hot || this.options.liveReload) {
-        this.createSocketServer();
-      }
+    return (
+      findPort(port || this.options.port)
+        // eslint-disable-next-line no-shadow
+        .then((port) => {
+          this.port = port;
 
-      if (this.options.bonjour) {
-        runBonjour(this.options);
-      }
+          return this.listeningApp.listen(port, hostname, (err) => {
+            if (this.options.hot || this.options.liveReload) {
+              this.createSocketServer();
+            }
 
-      this.showStatus();
+            if (this.options.bonjour) {
+              runBonjour(this.options);
+            }
 
-      if (fn) {
-        fn.call(this.listeningApp, err);
-      }
+            this.showStatus();
 
-      if (typeof this.options.onListening === 'function') {
-        this.options.onListening(this);
-      }
-    });
+            if (fn) {
+              fn.call(this.listeningApp, err);
+            }
+
+            if (typeof this.options.onListening === 'function') {
+              this.options.onListening(this);
+            }
+          });
+        })
+        .catch((err) => {
+          if (fn) {
+            fn.call(this.listeningApp, err);
+          }
+        })
+    );
   }
 
   close(cb) {