The reason the error is perhaps more unclear than it could be is because they assume you have read the Rust book or understand how blocks are expressions themselves.

I’m not so sure that this is the issue. I understood that blocks are expressions. The issue was that I didn’t know that type inference doesn’t apply to function returns (generally). That such is not true is easy to guess, but I’d presumed as much because the task of inferring seemed no more difficult than local variable type inference.

And so given that it’s such a simple and essential requirement, I’m not sure it wouldn’t be simpler and better to have a compiler error that simply states that an explicit return type is required.

Seeing instead that the return type was understood to be the unit type is also confusing as the function block clearly had a return value (here, AFAIU, explicit/implicit return makes no difference). So instead of wondering about the need for an explicit return type I immediately wondered about what type the function was actually returning (ie, had I accidentally created ()).

Of course I didn’t know about the unit type etc. But even so, as a compiler error, it’s represented in pieces rather than cutting to the core requirement of an explicit return type. Perhaps a reminder better left to a linter. I’d guess clippy warns you about this, but I thought I’d just rely on the compiler for as long as I can.