[Pre-RFC] Implicit number type widening

[scottmcm]

@Tom-Phinney

What your example really demonstrates is the danger of Rust’s as operator, which can silently truncate even when that is not the intent.

I completely agree. It's often the easiest thing to reach for, and thus it often gets used even when there are other options that might be better (and clippy will suggest) -- so we need either to add ways that are more-ergonomic than as or discourage/deprecate as.