The following code is legal:

fn get_mut_ref<'a>() -> &'a mut [u8] { &mut [] }

However, if we instead use (), it's no longer legal:

fn get_mut_ref<'a>() -> &'a mut () { &mut () }

We get this error:

error[E0515]: cannot return reference to temporary value --> src/lib.rs:2:5 | 2 | &mut () | ^^^^^-- | | | | | temporary value created here | returns a reference to data owned by the current function 

Is there a reason that the former is legal while the latter is not? I would expect the latter to be legal - in the general case, it'd be great if it were legal for any ZST, although I'm sure that's more complicated (especially in a generic context).

On Fuchsia, we're currently using this hack to work around this limitation.