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

Question

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
```