new lint: `unnecessary_faillible_conversion`

[sosthene-nitrokey]

What it does

This lint would warn against using try_into from the TryInto or TryFrom trait when there is an available Into or From implementation.

Advantage

Remove the need for handling an error case that can never happen (if there is a From impl, the Error case of the TryFrom impl is Infallible.

Drawbacks

No response

Example

let a: u32 = 32;
let b: Result<u64, Infaillible> = a.try_into();

Could be written as:

let a: u32 = 32;
let b: u64 = a.into();

[y21]

@rustbot claim