Technically Rust could hint at the semantics, based on whether `set_href` returned `()` or `!`. However the “erroneous” usage would not be surfaced in the case

Technically Rust could hint at the semantics, based on whether `set_href` returned `()` or `!`. However the “erroneous” usage would not be surfaced in the case of a conditional redirect indeed (for a non-conditional one you may notice that the following code is not dead).