I think the compilers would be allowed to just make your default warning changes as non-fatal diagnostics aren't a conformance matter. So you probably need to l

I think the compilers would be allowed to just make your default warning changes as non-fatal diagnostics aren't a conformance matter. So you probably need to lobby GCC, Clang and MSVC. Herb's discussion of "unsafe" for Cpp2 is... misleading. Rust's unsafe does not turn off checking. If you take some safe Rust which compiles (even if it panics) and you just wrap that in a block with the unsafe keyword, all you get for your trouble is a new diagnostic (by default a warning) saying not to do that because it's futile to use an unsafe block here. No checks are switched off, no "performance" shortcuts are added, if it would panic before it still does now - it's just the same code with a frivolous "unsafe" sign on it.