`#[track_caller]` in miniextendr

The #[miniextendr] macro automatically adds #[track_caller] to Rust functions for better panic location reporting.

🔗What it does

When a panic occurs (e.g., from .unwrap(), .expect(), or assert!()), Rust reports the source location. With #[track_caller], the location propagates through the call chain, showing where the panicking function was called from rather than where the panic originated.

🔗Example

#[miniextendr]
pub fn process_data(x: i32) {
    let result: Option<i32> = None;
    result.unwrap();  // panics here
}

Without #[track_caller]: Panic reports the location inside Option::unwrap() in the standard library.

With #[track_caller] (automatic): Panic reports lib.rs:4 - the line where .unwrap() was called in your code.

🔗When it helps

The automatic #[track_caller] is most useful for panics from:

• .unwrap() and .expect() on Option and Result
• assert!(), assert_eq!(), assert_ne!()
• Any function that uses std::panic::Location::caller()

🔗When it doesn’t help

#[track_caller] does NOT affect:

• Direct panic!() calls - these always report their own location
• Argument conversion errors in the generated wrapper - these report the #[miniextendr] line
• extern "C-unwind" functions - these don’t support #[track_caller]

🔗Propagation through call chains

For #[track_caller] to propagate through multiple function calls, ALL functions in the chain need the attribute:

#[track_caller]
fn helper() {
    let x: Option<i32> = None;
    x.unwrap();
}

#[miniextendr]  // automatically adds #[track_caller]
pub fn my_function() {
    helper();  // panic location will be here if helper has #[track_caller]
}

Without #[track_caller] on helper(), the panic location shows inside helper() where unwrap() was called.

🔗Skipped cases

The macro does NOT add #[track_caller] when:

1. The function already has #[track_caller]
2. The function has an explicit ABI (e.g., extern "C-unwind")