Code compiles on playground but fails when passed via stdin to rustc

The relevant edition change for that error is 2021's IntoIterator for arrays.

Calls to IntoIterator::into_iter are hidden in Rust 2015 and Rust 2018 when using method call syntax (i.e., array.into_iter()). So, array.into_iter() still resolves to (&array).into_iter() as it has before.