WiFi config(): warning for legacy idioms (esp8266#9050)

cores/esp8266/LwipIntfDev.h

@@ -69,7 +69,10 @@ class LwipIntfDev: public LwipIntf, public RawDev
                    const IPAddress& arg3 = IPADDR_NONE, const IPAddress& dns2 = IPADDR_NONE);
 
     // two and one parameter version. 2nd parameter is DNS like in Arduino. IPv4 only
-    boolean config(IPAddress local_ip, IPAddress dns = INADDR_ANY);
+    [[deprecated("It is discouraged to use this 1 or 2 parameters network configuration legacy "
+                 "function config(ip[,dns]) as chosen defaults may not match the local network "
+                 "configuration")]] boolean
+    config(IPAddress local_ip, IPAddress dns = INADDR_ANY);
 
     // default mac-address is inferred from esp8266's STA interface
     boolean begin(const uint8_t* macAddress = nullptr, const uint16_t mtu = DEFAULT_MTU);

doc/esp8266wifi/station-class.rst

@@ -99,11 +99,11 @@ config
 
 Disable `DHCP <https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol>`__ client (Dynamic Host Configuration Protocol) and set the IP configuration of station interface to user defined arbitrary values. The interface will be a static IP configuration instead of values provided by DHCP.
 
-Note that to reenable DHCP, all three parameters as 0.0.0.0 (local_ip, gateway and subnet as ``INADDR_ANY``) must be passed back to config() and re-connecting is needed.
+Note that to reenable DHCP, all three parameters (local_ip, gateway and subnet) as IPv4 ``0U`` (= 0.0.0.0) must be passed back to config() and re-connecting is needed.
 
 .. code:: cpp
 
-    WiFi.config(local_ip, gateway, subnet)
+    WiFi.config(local_ip, gateway, subnet)             (for Arduino API portability, discouraged as chosen defaults may not match the local network configuration)
     WiFi.config(local_ip, gateway, subnet, dns1)
     WiFi.config(local_ip, gateway, subnet, dns1, dns2)
 
@@ -122,16 +122,18 @@ The following IP configuration may be provided:
    (like e.g. *www.google.co.uk*) and translate them for us to IP
    addresses
 
-For Arduino networking API compatibilty the ESP8266WiFi library supports for IPv4 additional versions of the ``config`` function.
+For Arduino networking API compatibility, the ESP8266WiFi library supports IPv4-only additional versions of the ``config`` function:
 
 .. code:: cpp
 
-    WiFi.config(local_ip)
-    WiFi.config(local_ip, dns)
-    WiFi.config(local_ip, dns, gateway)
+    WiFi.config(local_ip)                        (for Arduino API portability, discouraged as chosen defaults may not match the local network configuration)
+    WiFi.config(local_ip, dns)                   (for Arduino API portability, discouraged as chosen defaults may not match the local network configuration)
+    WiFi.config(local_ip, dns, gateway)          (for Arduino API portability, discouraged as chosen defaults may not match the local network configuration)
     WiFi.config(local_ip, dns, gateway, subnet)
 
-Versions where some of ``dns``, ``gateway`` and ``subnet`` parameters are not specified use a default value. Default ``subnet`` is 255.255.255.0. Default ``gateway`` and ``dns`` are derived from ``local_ip`` by changing the last number to 1. To return to DHCP you can use ``WiFi.config(INADDR_NONE);``.
+Versions where some of ``dns``, ``gateway`` and ``subnet`` parameters are not specified use a default value. Default ``subnet`` is 255.255.255.0. Default ``gateway`` and ``dns`` are derived from ``local_ip`` by changing the last number to 1. It is discouraged to use these default values as they may not apply to every network configuration.
+
+Reminder : To reenable DHCP you can use ``WiFi.config(0U, 0U, 0U);``.
 
 **Warning: The default values for dns, gateway and subnet may not match your router's settings.** Also please note, that ``config(local_ip, gateway)`` is not supported and ``WiFi.config(local_ip, gateway, subnet)`` doesn't set the DNS server IP.
 

libraries/ESP8266WiFi/src/ESP8266WiFiSTA.h

@@ -49,6 +49,7 @@ class ESP8266WiFiSTAClass: public LwipIntf {
 
         // two and one parameter version. 2nd parameter is DNS like in Arduino
         // IPv4 only
+        [[deprecated("It is discouraged to use this 1 or 2 parameters network configuration legacy function config(ip[,dns]) as chosen defaults may not match the local network configuration")]]
         bool config(IPAddress local_ip, IPAddress dns = INADDR_ANY);
 
         bool setDNS(IPAddress dns1, IPAddress dns2 = INADDR_ANY);