`#[track_caller]` cannot be used in traits yet. This is due to limitations in
the compiler which are likely to be temporary. See [RFC 2091] for details on
this and other restrictions.
Erroneous example with a trait method implementation:
```compile_fail,E0738
#![feature(track_caller)]
trait Foo {
fn bar(&self);
}
impl Foo for u64 {
#[track_caller]
fn bar(&self) {}
}
```
Erroneous example with a blanket trait method implementation:
```compile_fail,E0738
#![feature(track_caller)]
trait Foo {
#[track_caller]
fn bar(&self) {}
fn baz(&self);
}
```
Erroneous example with a trait method declaration:
```compile_fail,E0738
#![feature(track_caller)]
trait Foo {
fn bar(&self) {}
#[track_caller]
fn baz(&self);
}
```
Note that while the compiler may be able to support the attribute in traits in
the future, [RFC 2091] prohibits their implementation without a follow-up RFC.
[RFC 2091]: https://github.com/rust-lang/rfcs/blob/master/text/2091-inline-semantic.md