How to disable unused code warnings in Rust?
WarningsCompiler WarningsRustDead CodeWarnings Problem Overview
struct SemanticDirection;
fn main() {}
warning: struct is never used: `SemanticDirection`
--> src/main.rs:1:1
|
1 | struct SemanticDirection;
| ^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: #[warn(dead_code)] on by default
I will turn these warnings back on for anything serious, but I am just tinkering with the language and this is driving me bats.
I tried adding #[allow(dead_code)]
to my code, but that did not work.
Warnings Solutions
Solution 1 - Warnings
You can either:
-
Add an
allow
attribute on a struct, module, function, etc.:#[allow(dead_code)] struct SemanticDirection;
-
Add a crate-level
allow
attribute; notice the!
:#![allow(dead_code)]
-
Pass it to
rustc
:rustc -A dead_code main.rs
-
Pass it using
cargo
via theRUSTFLAGS
environment variable:RUSTFLAGS="$RUSTFLAGS -A dead_code" cargo build
Solution 2 - Warnings
Another way to disable this warning is to prefix the identifier by _
:
struct _UnusedStruct {
_unused_field: i32,
}
fn main() {
let _unused_variable = 10;
}
This can be useful, for instance, with an SDL window:
let _window = video_subsystem.window("Rust SDL2 demo", 800, 600);
Prefixing with an underscore is different from using a lone underscore as the name. Doing the following will immediately destroy the window, which is unlikely to be the intended behavior.
let _ = video_subsystem.window("Rust SDL2 demo", 800, 600);
Solution 3 - Warnings
Making the code public also stops the warnings; you'll need to make the enclosing mod
's public too.
This makes sense when you're writing a library: your code is "unused" internally because it's intended to be used by client code.
Solution 4 - Warnings
Put these two lines on the top of the file.
#![allow(dead_code)]
#![allow(unused_variables)]
Solution 5 - Warnings
also as an addition: rust provides four levels of lints (allow, warn, deny, forbid).
https://doc.rust-lang.org/rustc/lints/levels.html#lint-levels
Solution 6 - Warnings
You can always disable unused variables/functions by adding an (_) to the variable name, like so:
let _variable = vec![0; 10];
Solution 7 - Warnings
For unused functions, you should make the function public, but watch out. If the struct isn't public, then you'll still get the error as in here:
//this should be public also
struct A{
A{}
}
impl A {
pub fn new() -> A {
}
}
Or if you don't want it to be public, you should put #[allow(unused)]
Solution 8 - Warnings
using features
#[cfg(feature = "dead_code")]
note: "dead_code"
can be replaced by any word.