> The argument for using Rust instead of a memory safe implementation of C is all about performance. And that’s not a bad argument! But we should be honest about it.
This is half of it; the other half is that there's more to writing correct code than just memory safety.
Rust was not initially designed as a memory-safe "C alternative" -- it started as a higher level language with green threading and garbage collection. Borrow checking, affine types, and all that were introduced not to "solve" memory safety, but to reduce logic bugs in complex, highly concurrent code by enabling programmers to statically check application invariants using the type system. Once it became apparent that this system was powerful enough to express the semantics of full memory safety without garbage collection, GC was removed from the core of the language, and Rust became what it looks like now.
The point is, I think focusing on "memory safety" seriously undersells Rust. Rust is aimed at giving you tools to statically verify arbitrary correctness properties of your program; and memory safety is just one example of how the standard library uses the available tooling to prove one particularly useful property. But Rust's "safety" protects you from any logic bug that you define to be a safety issue.
Additionally, this means that you're not restricted to one particular runtime or environment's ideas of memory safety -- you can write or bring in unsafe code to define your own requirements. This is very important to me -- I work on low-level driver and RTOS code for microcontrollers, and am commonly doing very unsafe things with task switching, interrupts, DMA, memory layout and pointer casting tricks, inline assembly, hardware MMIO, power management, etc. Rust fits fantastically in this niche, because I can use the type system to write out all the preconditions that external users must uphold when interacting with my driver code.
I think Fil-C is an excellent project, and is far more practical and realistic than TRACTOR for the problem of securing legacy code. But I also see it as largely orthogonal to Rust -- I can't see many situations where someone would choose Fil-C for greenfield code over something like Java or Go. Rust has safety, performance, and interop advantages over GC'd languages; and safety advantages over other C-like languages; so it's a great choice for new projects, but it's not gonna help you with all your old code like Fil-C will.
> It’s also annoying that this DARPA page mentions some kind of consensus. There’s no consensus on Rust being the safe bet.
The "consensus" the article talks about is not Rust, it's that "relying on bug-finding tools is not enough." Swift, C++-with-[the right]-changes, and Fil-C all would fall within that consensus (of needing some sort of guaranteed safety); only Zig is something of an exception in your list.