[Rust] impl Follow for bool is unsound

[nagisa]

The implementation impl Follow for bool is defined here and ends up calling read_scalar_at::<bool>(...). read_scalar_at (defined here) is for all intents and purposes a transmute and therefore given a byte that is not exactly 0 or 1 will produce a value of bool that has an invalid underlying bit pattern. That is UB in Rust. Invoking it is as easy as

bool::follow(b"\x42", 0)

or something along the lines.

[aardappel]

Might be as simple as adding != 0 after the read_scalar_at call, and change its type to u8 or whatever?

@rw

[nagisa]

Yes.

[rw]

@nagisa Nice catch! Want to try fixing that with a PR? You'd remove the line

impl_follow_for_endian_scalar!(bool);

and implement a new follow function for bool.

[nagisa]

I would if SLA was not required – not really interested in dealing with the legalese.