962e21cf15
Add unit-hash lint
changelog: [`unit_hash`] Add lint for hashing unit values
This will lint for situations where the end user is attempting to hash a unit value (`()`), as the implementation in `std` simply [does nothing][impl]. Closes #7159 .
Example:
```rust
().hash(&mut state);
// Should (probably) be replaced with:
0_u8.hash(&mut state);
```
[impl]: a5f164faad/library/core/src/hash/mod.rs (L656)