add libmaple STM32F1 SoftwareSerial capable define

[GerogeFu]

If you add this , so i can add software serial for stm32f1 boards.

[teemuatlut]

Thanks!

[thinkyhead]

For some reason some of our STM32F1x platforms can find <SoftwareSerial.h> while others cannot. See recent comments on MarlinFirmware/Marlin#14832

[tpruvot]

Which pio/arduino lib are you using for the STM32 ?

[teemuatlut]

@thinkyhead Do you know how many of our build tools support __has_include?

[thinkyhead]

I have been told that we can use #ifdef __has_include to check for its existence, because it is a builtin of the preprocessor.

[thinkyhead]

Aha, actually this did work. Not sure if it works with defined(__has_include) on the same line as the test.

#ifdef __has_include
  #if __has_include(<Arduino.h>)
    #error "Arduino.h is seen by __has_include!"
  #else
    #error "Arduino.h is NOT seen by __has_include!"
  #error
#endif

[thinkyhead]

Nope. Don't do this:

#if defined(__has_include) && __has_include(<Arduino.h>)

[tpruvot]

its not that some find it.. its just all the F1 which doesnt find it.. Others does not include it at all. This release change is only for STM32F1 (ARDUINO_ARCH_STM32F1)

[teemuatlut]

b9b3796

[thinkyhead]

That patch will be helpful to future-proof the library. So basically, any platform that's using C++17 will be able to avoid the include automagically. But note that if the library isn't installed, there will be no #include error. But other undefined symbol errors will still pop up.

[teemuatlut]

Yea if the library isn't installed (maybe because the platform doesn't have it), then you can't use SW Serial. Makes sense to me but I need to think about whether or not I want to add a more verbose warning of some sort.
I think C++ had a deleted or deprecated features I could use if a user was trying to invoke a constructor the compiler doesn't have access to.

[thinkyhead]

I think C++ had a deleted or deprecated features I could use…

I've seen some tricks employed to add warnings to deprecated things and errors to obsolete things, but I've never seen official support in C++ yet. But I grabbed the new specification PDF so I'll see if it mentions it.

[thinkyhead]

Ah, yes. Here it is…

[[ deprecated ]] void hello() { printf("Hello"); }

[thinkyhead]

And we also have… [[ maybe_unused ]] which will allow us to get rid of UNUSED(thing) eventually.

[teemuatlut]

Also see https://en.cppreference.com/w/cpp/language/function#Deleted_functions

Any use of a deleted function is ill-formed (the program will not compile).

[GerogeFu]

@teemuatlut
I think we can change ARDUINO_ARCH_STM32F1 to ARDUINO_ARCH_STM32 to support all stm32 not only stm32f1. I am writing the lib to support it.
https://github.com/FYSETC/SoftwareSerialM
And maybe someday we can add it to Marlin.