That won't necessarily be enough to save you either because the existing warnings can still change. Here's some Rust code use foo; fn my_function() {

That won't necessarily be enough to save you either because the existing warnings can still change. Here's some Rust code use foo; fn my_function() { use foo; foo::other_function() } This used to not trigger a warning. In rustc 1.35, the existing warning unused_imports became smarter and could now detect the redundant import of foo. This resulted in several crates that had made unused item warnings into errors having the exact problem you said. I think -Werror is a bad idea in general.