When Rust calls into C code it completely loses almost all of its safety guarantees. Having a codebase which is half C and half Rust sounds worse to read and reason about than all either.
Additionally, most Windows code is C++ with Windows specific language extensions (COM, Structured Exception Handling, and others).
I think most C++ code should be rewritten in Rust library by library, but most software is not properly constructed as a series of libraries. And asking a business to rewrite working code in a brand new language instead of fixing a buffer overflow is a difficult ask.
> When Rust calls into C code it completely loses almost all of its safety guarantees.
Not really, it means that if there is a memory safety bug it must be either in an unsafe block or foreign C code (which also must be called in an unsafe block). While technically any C code could completely invalidate Rust's memory model, in practice that is almost always a C bug which you can debug more easily if much less of your codebase is in C (or equivalently, unsafe Rust).
> Having a codebase which is half C and half Rust sounds worse to read and reason about than all either.
I think that really depends how it's structured. You would probably want to avoid something like Rust calling C calling Rust calling C (calling Rust calling ... etc), but if the codebase is already separated into modules or even separate libraries you could rewrite a library or module while maintaining the same C API (and that Rust or C module can be read independently from the rest of the codebase).
COM is not windows specific, and it doesn’t require any language extensions. You can implement and consume these objects with GCC on ARM Linux just fine: https://github.com/Const-me/ComLightInterop
Additionally, most Windows code is C++ with Windows specific language extensions (COM, Structured Exception Handling, and others).
I think most C++ code should be rewritten in Rust library by library, but most software is not properly constructed as a series of libraries. And asking a business to rewrite working code in a brand new language instead of fixing a buffer overflow is a difficult ask.