This was one of the most redeeming things about Objective-C. It is a superset of C, and when I was working with it, I found myself writing the high-level stuff in ObjC, but with a lot of pure-C functions sprinkled in. It was really nice for working with C libraries like OpenGL, because you could find an example online and directly apply it without going through any kind of translation step. It was a really cool feature to have.

I share a similar experience with C++.

However that compatibility is also what makes Objective-C and C++ impossible to ever be fully safe, without breaking compatibility with the C subset.

Static analysis help, but only when all code is available.

It isn’t so black and white.

Nim, if you let it use C as a backend, will let you use C macros, despite being generally safe and not remotely a C superset.

Yes, the use of C macros (and any kind of ffi) is unsafe, that cannot be avoided. But it doesn’t need to be a c superset (and indeed, when you use JS as a backend, or the native LLVM backend, you get no access to C macros)

It's probably impossible in general, but you could probably deal with a bunch of common cases fairly easily (like constants)