Fix crate collections for no-std

Add missing type alias for `HashSet`, and better
separation of cfg feature attributes.

Author: ValuedMammal

src/lib.rs

@@ -35,14 +35,17 @@ pub use selection::*;
 pub use selector::*;
 pub use signer::*;
 
+#[cfg(feature = "std")]
 pub(crate) mod collections {
     #![allow(unused)]
-
-    #[cfg(feature = "std")]
     pub use std::collections::*;
+}
 
-    #[cfg(not(feature = "std"))]
+#[cfg(not(feature = "std"))]
+pub(crate) mod collections {
+    #![allow(unused)]
     pub type HashMap<K, V> = alloc::collections::BTreeMap<K, V>;
+    pub type HashSet<T> = alloc::collections::BTreeSet<T>;
     pub use alloc::collections::*;
 }