3.0.0 migration docs inaccuracy

[rachel-bousfield]

Right here in the 2.3 to 3.0.0 migration docs we have the following excerpt

pub struct MyEnv {
    pub memory: Option<Memory>,
    pub alloc_guest_memory: Option<TypedFunction<i32, i32>>,
    pub multiply_by: u32,
}

let env = FunctionEnv::new(&mut store, MyEnv {
  memory: None,
  alloc_guest_memory: None,
  multiply_by: 10,
});

let instance = Instance::new(&module, &imports);
let mut env_mut = env.as_mut(&mut store);
env_mut.memory = Some(instance.exports.get_memory("memory"));
env_mut.alloc_guest_memory = Some(instance.exports.get_typed_function("__alloc"));

Observe that Instance::new, however, requires a &mut store as the first argument.
Unfortunately doing so now means two mutable references to store are alive at the same time, so the example will have to be reworked beyond the straightforward

let instance = Instance::new(&mut store, &module, &imports);

[syrusakbary]

That's a great catch. We need to fix this

[w-flo]

Also, this sets the memory: Option<Memory> field in the MyEnv struct to Some(instance.exports.get_memory("memory")), which is a Result<>, so something like unwrap is needed. Even after the unwrap, it's &Memory instead of Memory so that won't work.

I came to this bug report to find out how to access linear memory in a host function, and it looks like I need a different approach. :-)

Edit: My comment is actually bug #3399 , so the fix is easy: clone the Memory from its reference.

[ptitSeb]

Fixed in 3.2.1.