What it does

Aim would be to warn when intended Deref is not triggered correctly.

E.g. for https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=c78429c73f85949bd3799a9fdcaa4d74

use std::ops::Deref; struct TestType; impl Deref for TestType { type Target = str; fn deref(&self) -> &Self::Target { "test" } } impl std::fmt::Display for TestType { fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result { write!(f, "{}", &**self) } } fn main() { let test = TestType {}; println!("Hello, world!, {}", test); }

If we write:

 write!(f, "{}", &self)

or

 write!(f, "{}", &*self)

Then the Deref to str is not triggered and we got a stack overflow due to recursively calling Display::fmt

At the moment there are no clippy or rustc warnings or errors, and we just get a stack overflow.

Categories (optional)

• Kind: clippy::suspicious

What is the advantage of the recommended code over the original code

The recommended code correctly triggers the Deref and avoids the stack overflow.