This is cool and will likely enable some cool tooling.
I don't think a borrow checker is likely to be in that tooling. Borrow checking requires shaping the code, and all the dependencies, into easily analyzable (and at least in rust's version annotated) patterns. You can't borrow check arbitrary code not designed for it without false positives.
That's not sufficient - consider the following pseudocode
x = malloc();
if (opaque_cond()) free(x);
if (other_opaque_cond()) use(x);
Conditions can be opaque and non-analyzable due to rices theorem - in any turing complete language. This code is correct (or at least not memory unsound) if opaque_cond and other_opaque_cond are never both true. Otherwise it isn't.
And functionally compiler analyses of whether conditions hold have to be trivial because using some form of theorem prover to decide of code is correct or not leads to code that is brittle against compiler version changes, and slow compile times. Thus opaque_cond could be as simple as `len == 0` and `other_opaque_cond` could be `len > 0` and it's unlikely you'd want the compiler to realize those are mutually exclusive (at the stage where it accepts programs, obviously during optimization it is very likely to take advantage of this).
Rust solves this by simply rejecting the pattern. Very roughly forcing you to write if opaque_cond() { free(x) } else if other_opaque_cond() { use_x } (or something else where the program structure and not just the logic in the conditions guarantees correctness). Zig simply allows it and leaves it up to the programmer not to make a mistake.
And as onlyrealcuzzo suggests aliases are where this type of analysis (accepting enough programs to be useful but still imposing enough structure you can prove correctness) is really tricky.
It's possible to detect and ban the version of the problematic pattern that I made as short and simple as possible to illustrate the point, sure.
I'm general though, I don't believe it is practical to do so. Not without every library being designed with the checker in mind and annotated to more precisely describe their APIs. Which is why I'm not surprised to see the limitations.md that seems to exclude all the hard cases (aliasing, pointers used as first class values, cross function analysis): https://github.com/ityonemo/clr/blob/main/LIMITATIONS.md#mem...
Obviously if you rewrite the zig world to obey rust like rules and include rust like annotations you can implement a rust like borrow checker, but I don't think that it would still be meaningfully zig. It might be an interesting language worth exploring.
i dont understand the downvotes here. the point of any safety checker is to flag and ban potentially unsafe code, and force the author to rewrite with existing language patterns that guarantee the desired safety parameters.
in this case, zig has a first class nullable syntax that the checker can use ti guarantee correctness for, so a checker can deterministically sidestep this turing completeness issue, by squeezing indeterminate code into the knowably safer language idiom.
1. rust didnt invent affine ownership. 2. It's possible to bolt on to other languages (see ada). zig in particular is easy (disclaimer: i think, i haven't implemented it yet)
> zig in particular is easy (disclaimer: i think, i haven't implemented it yet)
I guess it's "easy" compared to other languages - but if you think it's "easy", we have different definitions of "easy".
You could implement it, but it would look like efforts in Rust to get SPARK-like safety, and SPARK itself. It will essentially be a different language.
You will not be able to work seamlessly with any regular Zig code. That may or may not be a problem if you're willing to assume you can just use it all unsafely and it works enough that things are fine.
That's somewhat analogous to unsafe Rust. The difference with unsafe Rust is... That's a very small fraction of what you're using, not the vast majority of what you use.
When you use a Rust crate - you generally do not expect that it could have infinite race conditions. It may have some unsafe code, but that should be the exception, not the norm.
By all means, please build it. I'd consider using it [=
intermediate representation. attempting to analyze zig code directly would be too hard (especially with comptime). on the way to the compiler backend, the compiler builds a simplified representation that only has "actually existing functions" and is very straightforward, e.g.
function 10112:
0: argument 0
1: argument 1
2: argument 2
3: add 0, 1
4: store 2
5: call function 1342, (2, 4)
6: return 5
you can see how building a data dependency graph from this would be easy.