How do you disable dead code warnings at the crate level in Rust?

While tinkering in Rust, I repeatedly encountered a lot of dead code warnings that made it difficult to focus. I tried using the outer attribute #[allow(dead_code)], but it only silences one warning at a time.
struct SemanticDirection;

fn main() {}

warning: struct SemanticDirection is never constructed
--> src\main.rs:1:8
|
1 | struct SemanticDirection;
| ^^^^^^^^^^^^^^^^^
|
= note: #[warn(dead_code)] on by default


How do I disable these warnings at the crate level?

You can either:

-
Add an allow attribute on a struct, module, function, etc.:

#[allow(dead_code)]
struct SemanticDirection;

-
Add an allow as a crate-level attribute; notice the !:

#![allow(dead_code)]

-
Pass it to rustc:
rustc -A dead_code main.rs


-
Pass it using cargo via the RUSTFLAGS environment variable:
RUSTFLAGS="$RUSTFLAGS -A dead_code" cargo build


Stack Overflow Q#25877285, score: 908