RS.CLIPPY.RECURSIVE_FORMAT_IMPL

Format trait method called while implementing the same Format trait

This checker is a Clippy lint created by The Rust Project Contributors. The documentation shown here is a copy of the original documentation for: recursive_format_impl. Copyright ©2025 The Rust Team. All rights reserved.

What it does

Checks for format trait implementations (e.g. Display) with a recursive call to itself which uses self as a parameter. This is typically done indirectly with the write! macro or with to_string().

Why is this bad?

This will lead to infinite recursion and a stack overflow.

Example

use std::fmt;

struct Structure(i32);
impl fmt::Display for Structure {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.to_string())
    }
}

Use instead:

use std::fmt;

struct Structure(i32);
impl fmt::Display for Structure {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.0)
    }
}

Past names

to_string_in_display