Fuzz testing for SoAVec API

[Reinsdyret]

• feat(fuzz): implement SoAVec API fuzzer

Still needs to fuzz some structs with Drop implementation before review.

[aapoalas]

suggestion: You could maybe use something like black_box on the reference to ensure the compiler doesn't optimise this down to nothing. Also consider dereferencing the value here and putting that into black_box go confirm reading works. Do the same for mut side, but there if possible also write a value through the mut reference.

[Reinsdyret]

Ok! So I've just maybe cleaned up the code a little and added black boxes.
I haven't made any structs with references because i don't understand it really, arbitrary cannot generate structs with referred values. But I am reading on something with std::borrow::Cow? Would this be correct to use like

#[derive(Arbitrary, Debug)]
struct MyStruct<'a> {
    name: Cow<'a, str>,
}

And for the custom Drop implementation structs i don't think there is a way unless the whole struct is very simple as in a struct that only has Copy types. Is this what you wanted?

[aapoalas]

Ok! So I've just maybe cleaned up the code a little and added black boxes. I haven't made any structs with references because i don't understand it really, arbitrary cannot generate structs with referred values.

Hmm... I could imagine eg. creating some static array of values of type T, and then randomly generating an index into that array and borrowing that index from the array, and thus generate &T types. But that definitely seems like it needs something more than just Arbitrary.

And for the custom Drop implementation structs i don't think there is a way unless the whole struct is very simple as in a struct that only has Copy types. Is this what you wanted?

I was thinking of something like using Box::leak or Vec::into_raw_parts to get things that must be manually dropped, and storing them inside your own custom type. Then impl Drop on that struct to perform Box::from_raw / Vec::from_raw_parts to deallocate the data on drop (Vec is a better example here); finally manually impl SoAble on that type with MUST_DROP_AS_SELF.

So for the Vec part an example would be:

struct SoableVec<T> {
  ptr: *mut T,
  length: usize,
  capacity: usize,
}

You get those fields from Vec::<T>::into_raw_parts which is nightly only; so instead you have to use as_mut_ptr, len and capacity APIs to get the field values, then you std::mem::forget the Vec to stop it from dropping itself; this combines into effectively into_raw_parts. now impl Drop for SoableVec to perform from_raw_parts.

[aapoalas]

LGTM, nice work! <3