Feature: [Network] Ensure players fill in a name instead of defaulting to "Player"

src/lang/english.txt

@@ -2175,6 +2175,7 @@ STR_NETWORK_ERROR_SERVER_START                                  :{WHITE}Could no
 STR_NETWORK_ERROR_CLIENT_START                                  :{WHITE}Could not connect
 STR_NETWORK_ERROR_TIMEOUT                                       :{WHITE}Connection #{NUM} timed out
 STR_NETWORK_ERROR_SERVER_ERROR                                  :{WHITE}A protocol error was detected and the connection was closed
+STR_NETWORK_ERROR_BAD_PLAYER_NAME                               :{WHITE}Your player name has not been set. The name can be set at the top of the Multiplayer window
 STR_NETWORK_ERROR_WRONG_REVISION                                :{WHITE}The revision of this client does not match the server's revision
 STR_NETWORK_ERROR_WRONG_PASSWORD                                :{WHITE}Wrong password
 STR_NETWORK_ERROR_SERVER_FULL                                   :{WHITE}The server is full

src/network/network.cpp

@@ -692,6 +692,8 @@ void NetworkClientConnectGame(NetworkAddress address, CompanyID join_as, const c
 
 	if (address.GetPort() == 0) return;
 
+	if (!NetworkValidateClientName()) return;
+
 	strecpy(_settings_client.network.last_host, address.GetHostname(), lastof(_settings_client.network.last_host));
 	_settings_client.network.last_port = address.GetPort();
 	_network_join_as = join_as;

src/network/network_client.cpp

@@ -1264,6 +1264,42 @@ bool NetworkIsValidClientName(const char *client_name)
 	return true;
 }
 
+/**
+ * Trim the given client name in place, i.e. remove leading and trailing spaces.
+ * After the trim check whether the client name is valid. A client name is valid
+ * whenever the name is not empty and does not start with spaces. This check is
+ * done via \c NetworkIsValidClientName.
+ * When the client name is valid, this function returns true.
+ * When the client name is not valid a GUI error message is shown telling the
+ * user to set the client name and this function returns false.
+ *
+ * This function is not suitable for ensuring a valid client name at the server
+ * as the error message will then be shown to the host instead of the client.
+ * @param client_name The client name to validate. It will be trimmed of leading
+ *                    and trailing spaces.
+ * @return True iff the client name is valid.
+ */
+bool NetworkValidateClientName(char *client_name)
+{
+	StrTrimInPlace(client_name);
+	if (NetworkIsValidClientName(client_name)) return true;
+
+	ShowErrorMessage(STR_NETWORK_ERROR_BAD_PLAYER_NAME, INVALID_STRING_ID, WL_ERROR);
+	return false;
+}
+
+/**
+ * Convenience method for NetworkValidateClientName on _settings_client.network.client_name.
+ * It trims the client name and checks whether it is empty. When it is empty
+ * an error message is shown to the GUI user.
+ * See \c NetworkValidateClientName(char*) for details about the functionality.
+ * @return True iff the client name is valid.
+ */
+bool NetworkValidateClientName()
+{
+	return NetworkValidateClientName(_settings_client.network.client_name);
+}
+
 /**
  * Send the server our name.
  */

src/network/network_func.h

@@ -37,6 +37,8 @@ extern StringList _network_ban_list;
 
 byte NetworkSpectatorCount();
 bool NetworkIsValidClientName(const char *client_name);
+bool NetworkValidateClientName();
+bool NetworkValidateClientName(char *client_name);
 void NetworkUpdateClientName();
 bool NetworkCompanyHasClients(CompanyID company);
 const char *NetworkChangeCompanyPassword(CompanyID company_id, const char *password);

src/network/network_gui.cpp

@@ -808,11 +808,9 @@ public:
 			}
 
 			case WID_NG_CLIENT:
-				if (NetworkIsValidClientName(this->name_editbox.text.buf)) {
+				/* Validation of the name will happen once the user tries to join or start a game, as getting
+				 * error messages while typing (e.g. when you clear the name) defeats the purpose of the check. */
 				strecpy(_settings_client.network.client_name, this->name_editbox.text.buf, lastof(_settings_client.network.client_name));
-				} else {
-					strecpy(_settings_client.network.client_name, "Player", lastof(_settings_client.network.client_name));
-				}
 				break;
 		}
 	}
@@ -1245,6 +1243,8 @@ static WindowDesc _network_start_server_window_desc(
 
 static void ShowNetworkStartServerWindow()
 {
+	if (!NetworkValidateClientName()) return;
+
 	DeleteWindowById(WC_NETWORK_WINDOW, WN_NETWORK_WINDOW_GAME);
 	DeleteWindowById(WC_NETWORK_WINDOW, WN_NETWORK_WINDOW_LOBBY);
 
@@ -1537,6 +1537,8 @@ static WindowDesc _network_lobby_window_desc(
  */
 static void ShowNetworkLobbyWindow(NetworkGameList *ngl)
 {
+	if (!NetworkValidateClientName()) return;
+
 	DeleteWindowById(WC_NETWORK_WINDOW, WN_NETWORK_WINDOW_START);
 	DeleteWindowById(WC_NETWORK_WINDOW, WN_NETWORK_WINDOW_GAME);