Suggest use of track_caller on assert-like functions

What it does

Suggest taking advantage of the #[track_caller] feature.

It's a less-known feature of Rust, but quite useful on assert-like functions which want to point out that their caller supplied invalid input. The attribute makes panics point to function's caller, e.g. a unit test, rather than internals of the helper function.

The attribute could be suggested on functions which contain panicking code (panic!, assert!) and are named assert_*. I'm not sure about the function name heuristic. Maybe it could be suggested on any "simple" panicking function, or functions called from any #[test], etc.

Categories (optional)

• Kind: pedantic, maybe style

Drawbacks

It's difficult to know for certain which functions are appropriate for use with #[track_caller].

Example

fn assert_not_zero(n: u32) {
    assert!(n != 0);
}

Could be written as:

#[track_caller]
fn assert_not_zero(n: u32) {
    assert!(n != 0);
}

Start by reviewing the proposed #[track_caller] use on assert_* functions and the alternatives involving panic!, assert!, or functions called from #[test]. Define a defensible scope and heuristic, then verify that the resulting lint correctly identifies suitable functions without flagging inappropriate cases.