Add bounds to type aliases (needed by rust-lang/rust#54033).

Author: eddyb

src/unify/backing_vec.rs

@@ -7,7 +7,8 @@ use std::marker::PhantomData;
 use super::{VarValue, UnifyKey, UnifyValue};
 
 #[allow(dead_code)] // rustc BUG
-type Key<S> = <S as UnificationStore>::Key;
+#[allow(type_alias_bounds)]
+type Key<S: UnificationStore> = <S as UnificationStore>::Key;
 
 /// Largely internal trait implemented by the unification table
 /// backing store types. The most common such type is `InPlace`,

src/unify/mod.rs

@@ -181,11 +181,13 @@ pub struct UnificationTable<S: UnificationStore> {
 }
 
 /// A unification table that uses an "in-place" vector.
-pub type InPlaceUnificationTable<K> = UnificationTable<InPlace<K>>;
+#[allow(type_alias_bounds)]
+pub type InPlaceUnificationTable<K: UnifyKey> = UnificationTable<InPlace<K>>;
 
 /// A unification table that uses a "persistent" vector.
 #[cfg(feature = "persistent")]
-pub type PersistentUnificationTable<K> = UnificationTable<Persistent<K>>;
+#[allow(type_alias_bounds)]
+pub type PersistentUnificationTable<K: UnifyKey> = UnificationTable<Persistent<K>>;
 
 /// At any time, users may snapshot a unification table.  The changes
 /// made during the snapshot may either be *committed* or *rolled back*.