ESP8266 fatal error: gdb_hooks.h: No such file or directory [solved]
Version 2.4.2 of the ESP8266 board definitions changed quite a lot of stuff that MySensors was using, so the current development version of MySensors (and most likely MySensors 2.3.1 when released) has been updated to accommodate those changes.
This means that MySensors dev/2.3.1+ only works with ESP8266 board definitions 2.4.2 and newer. If you use older versions, you'll get the following error:
In file included from ...\Arduino\libraries\MySensors/MySensors.h:420:0, from ...\Arduino\libraries\MySensors\examples\GatewayESP8266MQTTClient\GatewayESP8266MQTTClient.ino:114: ...\Arduino\libraries\MySensors/hal/architecture/ESP8266/MyMainESP8266.cpp:33:23: fatal error: gdb_hooks.h: No such file or directory #include "gdb_hooks.h" ^ compilation terminated. Using library ESP8266WiFi at version 1.0 in folder: ...\Arduino15\packages\esp8266\hardware\esp8266\2.4.1\libraries\ESP8266WiFi Using library MySensors at version 2.3.1-alpha in folder: ...\Arduino\libraries\MySensors Using library EEPROM at version 1.0 in folder: ...\Arduino15\packages\esp8266\hardware\esp8266\2.4.1\libraries\EEPROM Using library SPI at version 1.0 in folder: ...\Arduino15\packages\esp8266\hardware\esp8266\2.4.1\libraries\SPI exit status 1 Error compiling for board WeMos D1 R2 & mini.
The solution is to upgrade the ESP8266 board definitions using the Arduino IDE Boards Manager (Tools->Board->Boards manager) to version 2.4.2 or later.