This mistake also requires that the assignment operator has a result (and further, that the result can be silently coerced into a boolean for whatever reason)

In both Rust and Swift, this mistake doesn't compile, their assignment operators don't have a result and so it can't very well be true (or false) ‡

‡ Technically the result of Rust's assignment operators is the empty tuple, which is the closest to "doesn't have a result" in the type system. I don't know about Swift.