Error compiling for board...

I've had this problem more than once. Now I'm really disturbed, because I should finish my project in no time. I have a project where a maple (or stm32f103c) is connected to an esp8266 and the program has been working well, but now I need to update some features. Since my last update I've been working with other boards (ie. esp32), which I install googleing something like "esp32 index json" and then editing file preferences with a corresponding web address.

But I found out that after installing esp32 I can not find maple and esp8266 in the boards manager menu so I have to install them again. But the compiler doesn't want to compile it any more. I have tried previous versions of board packages, but getting always the same compiler error. I would not want to install the IDE again (that is how I got over the problem last time)

So am I installing/updating board packages somehow wrong? Why do boards disappear from the Tools menu? My code has not changed.

(deleted)

Well search "stm32 index json" gives me multiple results, but I remember choosing this line (because it has a man's name)

http://dan.drown.org/stm32duino/package_STM32duino_index.json

Ok, I did not have to install the Arduino IDE again - this is what worked for me. I chose Tools | Boards manager and searched for stm32. Now I chose the previous installation and removed it. Then I closed the programming environment and restarted it. I still had the same index.json in my preferences and reinstalled the same package. And everything was fine. So something must have happened during the previous installation of stm32 boards. I'm OK with the situation now.

Even after installing a package, you need to leave its Boards Manager URL in File > Preferences > Additional Boards Manager URLs. There is an icon on the right side of that field that makes it easy to add multiple URLs. If you remove the URLs then the boards will no longer show up in the Tools > Board menu after you open Boards Manager.

pert: Even after installing a package, you need to leave its Boards Manager URL in File > Preferences > Additional Boards Manager URLs. There is an icon on the right side of that field that makes it easy to add multiple URLs. If you remove the URLs then the boards will no longer show up in the Tools > Board menu after you open Boards Manager.

OK - small icon - big difference. Thanks!