How to get the current stack frame depth in Rust?

Question

How do I determine the current stack frame depth?

fn print_depths() {
    println!("stack frame depth {}", stack_frame_depth());
    fn print_depth2() {
        println!("stack frame depth {}", stack_frame_depth());
    }
    print_depth2();
}

pub fn main() {
    print_depths();
}

would print

stack frame depth 1
stack frame depth 2

I know main has callers so the particular numbers might be different.

I have tried stacker::remaining_stack. However, that prints a count of bytes remaining in the stack. Since the arguments passed to a function affect the stack byte "height" then it is not possible to derive a simple function call "height". I want a count of the current function call height.

Answer 1

If, having noted all the caveats in Peter Hall's answer, it is still desirable to obtain the actual stack depth, consider backtrace::Backtrace:

#[inline]
fn stack_frame_depth() -> usize {
    Backtrace::new_unresolved().frames().len()
}

See it on the playground.

If you want to avoid the allocation involved in instantiating a Backtrace, consider backtrace::trace instead:

#[inline]
fn stack_frame_depth() -> usize {
    let mut depth = 0;
    backtrace::trace(|_| {
        depth += 1;
        true
    });
    depth
}

Both of the above approaches require std for thread-safety, however. If your crate is no_std and/or you are ensuring synchronization some other way, there's backtrace::trace_unsynchronized.