Add `cast_known_wrap` for known bad casts in const contexts (`cast_possible_wrap`)

What it does

Casting between signed and unsigned constants is somewhat common, especially when working with C FFI (bindgen typically generates unsigned consts, C functions typically use signed ints).

This lint would check for as casts in const contexts and flag any where the RHS does not have the same value as the LHS.

Lint Name

cast_known_wrap

Category

pedantic

Advantage

Catch cases where a C #define doesn't fit into the expected value

Drawbacks

Noise when the cast is intended to just reinterpret the bit value

Example

#![warn(clippy::pedantic)]
#![warn(clippy::nursery)]

// OK conversion
const A: u32 = 1;
const B: i32 = A as i32;

// Failed conversion
const X: u32 = u32::MAX;
const Y: i32 = X as i32;
// const Z: i32 = X.try_into().unwrap(); // not possible in const


fn main() {
    println!("{A} {B}");
    println!("{X} {Y}");
}

Could be written as:

(no alternative - just a warning)

The issue names the existing cast_possible_wrap lint as the related entry point; start by locating it and reviewing how Clippy handles casts and const contexts. The issue provides no file or test path, so completion means defining and validating cast_known_wrap for const casts whose value changes, while avoiding warnings for equal-value conversions.