Fix Default for UnorderedSet

Summary: `UnorderedSet<T>` should implement `Default` even if `T` does not.

Reviewed By: JakobDegen

Differential Revision: D52788856

fbshipit-source-id: 10e9bc554696369e6ff63b4f73ea173421c6893e

starlark_map/src/unordered_set.rs

@@ -25,11 +25,18 @@ use crate::unordered_map::UnorderedMap;
 use crate::Equivalent;
 
 /// `HashSet` that does not expose insertion order.
-#[derive(Clone, Allocative, Debug, Default)]
+#[derive(Clone, Allocative, Debug)]
 pub struct UnorderedSet<T> {
     map: UnorderedMap<T, ()>,
 }
 
+impl<T> Default for UnorderedSet<T> {
+    #[inline]
+    fn default() -> UnorderedSet<T> {
+        UnorderedSet::new()
+    }
+}
+
 impl<T> UnorderedSet<T> {
     /// Create a new empty set.
     #[inline]