clippy::disallowed_names: use of a disallowed/placeholder name `foo`

What you see

warning: use of a disallowed/placeholder name `foo`
 --> main.rs:3:5
  |
3 | let foo = 3.14;
  |     ^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#disallowed_names
  = note: `#[warn(clippy::disallowed_names)]` 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?

These names are usually placeholder names and should be avoided.

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

let foo = 3.14;

Turn it off, or on

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

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

[lints.clippy]
disallowed_names = "allow"

cargo clippy -- -A clippy::disallowed-names

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.

Settings in clippy.toml

• disallowed-names: The list of disallowed names to lint about. NB: bar is not here since it has legitimate uses. The value ".." can be used as part of the list to indicate that the configured values should be appended to the default configuration of Clippy. By default, any configuration will replace the default value.