Bindings to std::function produce poor error messages

[mukunth1987]

I am trying to call c++ function which takes std::function as argument. But std::function is being interpreted as std::array

Below is my code.

test.h

#include "cxx.h"
#include <functional> 

class A {
  public:
     A() {}
     using RespHandler = std::function<void(int val)>;
     void sendRequest(RespHandler handler) {
          // handler(100);
     }
}

main.rs

use autocxx::prelude::*; 

include_cpp! {
    #include "test.h"
    safety!(unsafe)
    generate!("A")
} 

fn main() {
}

Cargo build error:

gen0.cxx: error: cannot convert 'void (A::*) (A::RespHandler)' {aka 'void (A::*) (std::function<void(int)>)'} to 'void (A::*) (std::array<long unsigned int, 4>)' in initialization

Specifications

autocxx = "0.25.0"
cxx = "1.0.94"

Could you please help if i miss something ?

[adetaylor]

Thanks - this is, I think, likely to be a limitation for a long time (I believe bindgen doesn't give us the right information, and even if it did, cxx does not yet support std::function. However these diagnostics are not OK, and I regard that as a bug.

[adetaylor]

FWIW when testing this by adding your code into the demo, I get something different. The build process says:

  Error:   × cxx couldn't handle our generated bindings - could be a bug in autocxx:
    │ unsupported type

This is because we are including this in the #[cxx::bridge] mod:

pub fn sendRequest(self: Pin<&mut A>, handler: [root::u128; 3usize]);

Solutions to improve this, then, would be one or several of the following:

• In bindgen, output something more useful than an array when it encounters such a type.
• In autocxx, during the function analysis phase, if we find a function has an array argument, then reject that function with a marginally more useful message. ("Arrays are not yet supported by cxx. Sometimes bindgen can generate arrays if it's not sure how to interpret a type, so the problem might be some other type not yet supported by bindgen.")
• Either way, include span information from bindgen so that we can point to a more useful location in our error messages