Clippy lints / Style
Clippy lint · Style · checked with Clippy 0.1.99
clippy::print_literal: literal with an empty format string
What it meansThis lint warns about the use of literals as print!/println! args. It is in the style group and warns by default.
What you see
warning: literal with an empty format string --> main.rs:3:16 | 3 | println!("{}", "foo"); | ^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#print_literal = note: `#[warn(clippy::print_literal)]` on by default help: try | 3 - println!("{}", "foo"); 3 + println!("foo"); |
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?
Using literals as println! args is inefficient (c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary (i.e., just put the literal in the format string)
Code that works but is not idiomatic Rust. Warns by default.
How to fix it
Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.
Flagged
println!("{}", "foo");
Write this instead
println!("foo");
Turn it off, or on
Allow it where it does not fit your code, as narrowly as you can:
On one item
#[allow(clippy::print_literal)]
fn my_function() { /* ... */ }Whole crate (Cargo.toml)
[lints.clippy]
print_literal = "allow"One run
cargo clippy -- -A clippy::print-literalThe [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.
Clippy's own documentation
What it does
This lint warns about the use of literals as print!/println! args.
Why is this bad?
Using literals as println! args is inefficient
(c.f., https://github.com/matthiaskrgr/rust-str-bench) and unnecessary
(i.e., just put the literal in the format string)
Example
println!("{}", "foo");
use the literal without formatting:
println!("foo");
From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.
Related lints
- needless_returnunneeded `return` statement
- new_without_defaultChecks for public types with a pub fn new() -> Self method and no implementation of Default
- len_zeroChecks for getting the length of something via .len() just to compare to zero, and suggests using .is_empty() where applicable
- option_map_or_noneChecks for usage of _.map_or(None, _)
- owned_cowneedlessly owned Cow type
- partialeq_to_nonebinary comparison to literal `Option::None`
- print_with_newlineThis lint warns when you use print!() with a format string that ends in a newline
- println_empty_stringempty string literal in `println!`
- ptr_argThis lint checks for function arguments of type &String, &Vec, &PathBuf, and Cow<_>
All 847 Clippy lints · Rust compiler errors · Cargo.toml checker
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