I realize that this should be an error rather than a warning. But one of the policies of Rust since 1.0 is to not break existing code, so any mechanism that det

I realize that this should be an error rather than a warning. But one of the policies of Rust since 1.0 is to not break existing code, so any mechanism that detects error that were not previously detected must make it a warning, rather than an error, otherwise some existing applications and libraries would stop compiling overnight. I generally find this a sane policy, but YMMV.