If you think you found a bug: you just open it. Reviewers / authors / community determine whether its a bug in the compiler or in the spec or both, or not. -

If you think you found a bug: you just open it. Reviewers / authors / community determine whether its a bug in the compiler or in the spec or both, or not. - How do you know that's something is a compiler bug? Compiler writers typically know. - How do you know that's something is a spec bug? All Rust spec changes go through the RFC process. If the proposal doesn't mention the issue, then its probably a bug. There are also many people maintaining the Rust spec. These people usually know. If nobody knows, you submit an RFC, explaining why you think is a bug. The community can then reading, and the appropriate teams can decide, and if it is merged, then it is a bug. The fix lands at some point, and the fixed Language / standard library / implementation becomes Rust 1.X.Y. Done. --- This is much simpler than in C++, where if you think you found a bug... you could open it in clang or gcc, but if its a spec bug, then that's the wrong place, and it might get closed with "not a bug". Ok so you need to open it in the spec, which you can do, but without you being an ISO member (and paying) there is little on your hand to push this forward.... Anyways supposed this is fixed in the spec, you then re-open it in the implementation you cared about. This might be fixed, or not. Probably not, because it would make this implementation incompatible with another existing one (e.g. clang incompatible with GCC), and that other one could say "fixing this breaks too much code, we won't fix it", so.... now you need to coordinate a bugfix deployment across multiple implementations. Even if you manage that, most fixes get backported, so that means these things introduce breaking changes in, e.g., old C++ standard versions, breaking old code that assumed those to be "stable", etc. And how these fixes are backported differs from compiler to compiler, so now you get a new set of incompatibilities. Some compilers like clang, have flags to configure which fixes get applied and which aren't (e.g. -fabi-compat=...) so that the user can choose which versions with which specification patches of which other compilers the generated code should be compatible with. How many bugs does the C++ spec have? Thousands: http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html What happens if you screw your C++ compatibility settings when mixing code from different toolchains (e.g. a library compiled with clang on linux with a binary compiled with gcc or viceveersa) ? Undefined behavior.