Unexpected compiler error when mistakenly pass a macro instead of function pointer

[hucancode]

I am writing some code and get the error

⚠️ The compiler encountered an unexpected error: "Should be unreachable".

- Function: sema_trace_decl_liveness(...)
- Source file: /build/5wc7gif967l539vxk1vly1prqrcfc0q3-source/src/compiler/sema_liveness.c:625

🙏 Please consider taking the time to file an issue on GitHub, so that we can get it fixed:

https://github.com/c3lang/c3c/issues/new so that we can get it fixed.

Minimum reproducable example would be as follow

import std::io;

struct Container {
  int[] items;
}

macro int Container.get(&this, usz i) @operator([]) {
  return this.items[i];
}

alias ProcGetItem = fn int(usz);
fn void process(int input, ProcGetItem getter) {
  io::printfn("%d", getter(1) + getter(2) + input);
}

fn void main() {
  Container c = {
    .items = { 2, 3, 4, 5 }
  };
  // &c.get is not an fn, this should produce compile error
  process(10, &c.get);
}

And also, unrelated to the error above but I want to ask the correct way to write this. I have a function that take a getter as parameter, I also have a container providing get operator. How to connect these two without the function depending on the container implementation?

[lerno]

This should be fixed now. For the problem you had, how would you write it in C?

[hucancode]

I can't find an equivalent in C, here is the C++ version of my intention. container.cpp only care about managing it's data. process.cpp only care about the business, they allow caller to pass an adder and it will call that while doing business.

// container.cpp
#include <vector>

struct Container {
    std::vector<int> items;
};

void container_add(Container* c, int value) {
    c->items.push_back(value);
}


// process.cpp
#include <iostream>

template<typename Adder>
void process(Adder adder, int a) {
    adder(a);
    std::cout << a <<" was just added to some container and I don't care about its implementation" << std::endl;
    // continue to the main business
}

// main.cpp
#include <functional>

int main() {
    Container my_container;
    auto adder = [&my_container](int value) {
        container_add(&my_container, value);
    };
    process(adder, 1);
    process(adder, 2);
    for (int item : my_container.items) {
        std::cout << item << " ";
    }
    return 0;
}