clippy::to_string_trait_impl: direct implementation of `ToString`

What you see

warning: direct implementation of `ToString`
  --> main.rs:8:1
   |
 8 | / impl ToString for Point {
 9 | |   fn to_string(&self) -> String {
10 | |     format!("({}, {})", self.x, self.y)
11 | |   }
12 | | }
   | |_^
   |
   = help: prefer implementing `Display` instead
   = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#to_string_trait_impl
   = note: `#[warn(clippy::to_string_trait_impl)]` on by default

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

This trait is automatically implemented for any type which implements the Display trait. As such, ToString shouldn’t be implemented directly: Display should be implemented instead, and you get the ToString implementation for free.

Code that works but is not idiomatic Rust. Warns by default.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

struct Point {
  x: usize,
  y: usize,
}

impl ToString for Point {
  fn to_string(&self) -> String {
    format!("({}, {})", self.x, self.y)
  }
}

Write this instead

struct Point {
  x: usize,
  y: usize,
}

impl std::fmt::Display for Point {
  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    write!(f, "({}, {})", self.x, self.y)
  }
}

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

#[allow(clippy::to_string_trait_impl)]
fn my_function() { /* ... */ }

[lints.clippy]
to_string_trait_impl = "allow"

cargo clippy -- -A clippy::to-string-trait-impl

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.