Auto prototype generation with function as argument to class instantiation

[per1234]

Using Arduino IDE 1.6.7 2015/11/07 12:42 with Windows 7 64 bit

I apologize if my terminology is off on the issue title, this is what I'm referring to:

#include "CallbackBug.h"
Task t1(&t1Callback);
void t1Callback() {}
void setup() {}
void loop() {}

CallbackBug.h:

#include <Arduino.h>
class Task {
  public:
    Task(void (*aCallback)()) {};
};

Compiling gives the error:

CallbackBug:3: error: 't1Callback' was not declared in this scope
 Task t1(&t1Callback);

If I declare the function prototype for t1Callback() it compiles fine.
The code compiles fine with Arduino IDE 1.6.5r5
Example of a library where this breaks the examples: https://github.com/arkhipenko/TaskScheduler
Originally reported at: http://forum.arduino.cc/index.php?topic=357312.msg2468586#msg2468586

[matthijskooijman]

The prototype for the t1Callback function is generated after the t1 variable. It seems the idea is to generate the prototypes just before the first function declaration, so they come after any type definitions they need (see https://github.com/arduino/arduino-builder/blob/master/src/arduino.cc/builder/prototypes_adder.go#L61). It seems this approach backfires for this testcase, unfortunately. I'm not sure if we can fix this automatically, since properly generating prototypes would require dependency analysis between all the elements in the source file and some complicated algorithm to find the proper order for them. I suspect this will become a wontfix issue, but I'll leave that to @ffissore.

ctags output:

t1Callback      /tmp/build5221f5af9dbac9dab29dc89b936a83f8.tmp/preproc/ctags_target.cpp /^Task t1(&t1Callback);$/;"     kind:variable   line:3
t1Callback      /tmp/build5221f5af9dbac9dab29dc89b936a83f8.tmp/preproc/ctags_target.cpp /^void t1Callback() {}$/;"      kind:function   line:4  signature:()  returntype:void
setup   /tmp/build5221f5af9dbac9dab29dc89b936a83f8.tmp/preproc/ctags_target.cpp /^void setup() {}$/;"   kind:function   line:5  signature:()    returntype:voidloop    /tmp/build5221f5af9dbac9dab29dc89b936a83f8.tmp/preproc/ctags_target.cpp /^void loop() {}$/;"    kind:function   line:6  signature:()    returntype:void

Preprocessed file:

#include <Arduino.h>
#line 1
#line 1 "/tmp/arduino_5221f5af9dbac9dab29dc89b936a83f8/sketch_nov09a.ino"
#include "Test.h"
Task t1(&t1Callback);
void t1Callback();
void setup();
void loop();
#line 3
void t1Callback() {}
void setup() {}
void loop() {}

[ffissore]

Yes indeed that's the source of the problem. I'm working on it. I've chatted with @facchinm and he told me that I can look at ctags "code" section and if it contains a "&" + one of the collected function names I can consider that a function pointer and use that line instead of "setup" one

[per1234]

I suspect this will become a wontfix issue

I kind of thought that might be the case, the user will just have to declare the prototype but I decided I'd at least report it so that you can put it on the list.

if it contains a "&" + one of the collected function names

I probably don't understand correctly but just in case this is any help, here's another sketch that was reported as being broken by 1.6.6, in this case they didn't use & before the function argument:

#include <TimedAction.h>

TimedAction timedAction = TimedAction(1000, blink);

void setup(){
  timedAction.enable();
}

void loop(){
  timedAction.check();
}

void blink(){
  // do stuff
}

That is using http://playground.arduino.cc/Code/TimedAction
Reported at: http://forum.arduino.cc/index.php?topic=357312.msg2469047#msg2469047

[ffissore]

Thank you @per1234 indeed that one won't work with that hack

[ffissore]

First type of function used as callback now works. Fix available with hourly builds. Second type however will NOT work. The only way to make it work is understanding that "blink" is a function pointer, which means having an Abstract Syntax Tree and/or C++ parser, which we don't have

[per1234]

Using Arduino IDE 1.6.7 2015/11/10 12:55
The following sketch still doesn't compile:

#include "CallbackBug.h"
// This doesn't compile:
Task t1(1000, &t1Callback);

// These all compile:
//Task t1 = Task(1000, &t1Callback);
//const unsigned long interval = 1000;
//Task t1(interval, &t1Callback);
//Task t1((unsigned long)1000, &t1Callback);

void t1Callback() {}
void setup() {}
void loop() {}

CallbackBug.h

class Task {
  public:
    Task(unsigned long aInterval, void (*aCallback)()) {};
};

Error:

CallbackBug:3: error: 't1Callback' was not declared in this scope
 Task t1(1000, &t1Callback);
                ^

This causes example sketches in the TaskScheduler library to not compile.

[NicoHood]

I think you need to remove the &. Look at the attach pin interrupt examples. They also dont need that. If this doesnt work, the taskscheduler library is probably coded wrong (while the bug might still exist, but the & syntax is bad for beginners anyways).

[matthijskooijman]

@NicoHood, that's not the case, the problem here is wrong ordering of prototypes, not the code itself. For functions, foo and &foo both result in the address of the function.