Rust Transmute without Unsafe!

This crate allows you to convert any type to any other type without the use of unsafe (thanks to the genius idea presented here: https://github.com/rust-lang/rust/issues/57893#issuecomment-500250283. Update: for compatibility with the next-generation trait solver, this library now makes use of this issue instead: https://github.com/rust-lang/rust/issues/133361).

It provides one function, implemented entirely in Safe Rust:

fn transmute<T, U>(x: T) -> U

Usable in projects that require dependencies to use #![forbid(unsafe_code)].

Never fight the borrow checker again!

All versions of Rust since 1.0 are supported.

Examples:

Sometimes you want to dereference a null pointer. This crate allows you to do so without any unsafe code.

let p = core::ptr::null_mut();
let x = transmute::<*mut i64, &'static i64>(p);
println!("{}", x); // BOOM

---

Sometimes you want to grow an array, but don't want to allocate more space. Thanks to modern technology, this is now possible to do safely™. Just steal the nearby memory with transmute.

let p = [0];
let mut x = transmute::<[u64; 1], [u64; 100]>(p);
// this slice now has 100 elements: yay so much space for our bytes
assert!(x.len() == 100);
x[50] = 42;

⚠️⚠️⚠️ WARNING ⚠️⚠️⚠️

THIS CRATE IS NOT SAFE.

This crate abuses a bug in the Rust compiler (https://github.com/rust-lang/rust/issues/57893) to circumvent the Rust type system.

Please do not actually use this.

Moral of the story: you cannot rely solely on Rust for supply chain security or isolation against an adversary. If you need adversarially-secure isolation, you should use sandboxing tools such as LFI or WebAssembly, or use hardware-based isolation via multiple processes or virtualization.