Better error message for boards without bootloader

[cmaglie]

Before:

$ arduino-cli upload -b arduino:avr:gemma -p /dev/ttyACM0
avrdude: invalid baud rate specified '{upload.speed}'
Error during Upload: uploading error: uploading error: exit status 1
$

After:

$ arduino-cli upload -b arduino:avr:gemma -p /dev/ttyACM0
Error during Upload: a programmer is required to upload for this board
$

[matthijskooijman]

Is this really the right place and right check for this? Looking at boards.txt, it would make more sense to check for the presence of upload.tool, which I think is used to lookup additional properties from platform.txt during upload. If that entry would be missing, that would be a clearer sign that regular upload is not supported.

One caveat is that currently e.g. the gemma does have a upload.tool specified, presumably since without it some other bit breaks (or used to break, maybe), so this would require changes in the platforms as well.

I haven't tested any of this, just commenting based on a quick review...

[cmaglie]

One caveat is that currently e.g. the gemma does have a upload.tool specified, presumably since without it some other bit breaks (or used to break, maybe), so this would require changes in the platforms as well.

Not only the gemma but a lot of other platforms like attiny, xmega, etc... They use this trick to force the Arduino IDE to perform an "upload-with-programmer" even if the user clicks on "upload".

The relevant part of the Arduino IDE is this: https://github.com/arduino/Arduino/blob/b3d609f4de066289088739747a743076cf4ea023/arduino-core/src/cc/arduino/packages/uploaders/SerialUploader.java#L87-L91

It's also specified in https://arduino.github.io/arduino-cli/dev/platform-specification/#upload-using-programmer-by-default

I'm going to merge it, but I'm happy to discuss a way to improve it if you have any idea.