Arbitrary is not implemented for HashMap (quickcheck)

[realcr]

Hi, thank you for your work on im-rs!

I am trying to compile the following code:

    use im::hashset::HashSet as ImHashSet;

    #[derive(Arbitrary, Clone)]
    struct ExampleHashSet {
        my_set: ImHashSet<u32>,
    }

    use im::hashmap::HashMap as ImHashMap;

    #[derive(Arbitrary, Clone)]
    struct ExampleHashMap {
        my_map: ImHashMap<u32, u64>,
    }

The first part (ExampleHashSet) compiles, but the second one (ExampleHashMap) does not. The second example fails with the following compilation error:

$ cargo test -p offst-proto
   Compiling offst-proto v0.1.0 (...)
error[E0277]: the trait bound `im::hash::map::HashMap<u32, u64>: quickcheck::arbitrary::Arbitrary` is not satisfied
   --> components/proto/src/funder/messages.rs:858:14
    |
858 |     #[derive(Arbitrary, Clone)]
    |              ^^^^^^^^^ the trait `quickcheck::arbitrary::Arbitrary` is not implemented for `im::hash::map::HashMap<u32, u64>`
    |
    = note: required by `quickcheck::arbitrary::Arbitrary::arbitrary`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
error: could not compile `offst-proto`.
warning: build failed, waiting for other jobs to finish...
error: build failed

This is the relevant line I have in my Cargo.toml:

im = {version = "14.1.0", features = ["serde", "quickcheck"]}

I am on the stable channel, this is the version of my rustc:

rustc 1.40.0 (73528e339 2019-12-16)

Guess for solution

I have seen this chunk of code at src/hash/map.rs:

#[cfg(all(feature = "arc", any(test, feature = "quickcheck")))]
impl<K: Hash + Eq + Arbitrary + Sync, V: Arbitrary + Sync> Arbitrary for HashMap<K, V> {
    fn arbitrary<G: Gen>(g: &mut G) -> Self {
        HashMap::from(Vec::<(K, V)>::arbitrary(g))
    }
}

It has the "feature = "arc". I am not sure what this feature is, and how to opt into it.
I did notice that it does not exist at src/hash/set.rs:

#[cfg(all(threadsafe, feature = "quickcheck"))]
impl<A, S> Arbitrary for HashSet<A, S>
where
    A: Hash + Eq + Arbitrary + Sync,
    S: BuildHasher + Default + Send + Sync + 'static,
{
    fn arbitrary<G: Gen>(g: &mut G) -> Self {
        HashSet::from_iter(Vec::<A>::arbitrary(g))
    }
}

[bodil]

Oops, yes, it looks like HashMap's Arbitrary implementation wasn't updates along with the rest of them when I got rid of the feature flags. Will fix.