Fix Arbitrary implementation on ArrayVec (#180)

- No longer needs to be guarded behind any feature.
- Can generate non full ArrayVecs.
- Implements size_hint.

src/arrayvec.rs

@@ -218,19 +218,29 @@ where
   }
 }
 
-#[cfg(all(feature = "arbitrary", feature = "nightly_const_generics"))]
-#[cfg_attr(
-  docs_rs,
-  doc(cfg(all(feature = "arbitrary", feature = "nightly_const_generics")))
-)]
-impl<'a, T, const N: usize> arbitrary::Arbitrary<'a> for ArrayVec<[T; N]>
+#[cfg(feature = "arbitrary")]
+#[cfg_attr(docs_rs, doc(cfg(feature = "arbitrary")))]
+impl<'a, A> arbitrary::Arbitrary<'a> for ArrayVec<A>
 where
-  T: arbitrary::Arbitrary<'a> + Default,
+  A: Array,
+  A::Item: arbitrary::Arbitrary<'a>,
 {
   fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
-    let v = <[T; N]>::arbitrary(u)?;
-    let av = ArrayVec::from(v);
-    Ok(av)
+    let max_len = A::CAPACITY.min(u16::MAX as usize) as u16;
+    let len = u.int_in_range::<u16>(0..=max_len)?;
+    let mut self_: Self = Default::default();
+    for _ in 0..len {
+      self_.push(u.arbitrary()?);
+    }
+    Ok(self_)
+  }
+
+  fn size_hint(depth: usize) -> (usize, Option<usize>) {
+    arbitrary::size_hint::recursion_guard(depth, |depth| {
+      let max_len = A::CAPACITY.min(u16::MAX as usize);
+      let inner = A::Item::size_hint(depth).1;
+      (0, inner.map(|inner| 2 + max_len * inner))
+    })
   }
 }