support atoms with empty slot

src/atom/mod.rs

@@ -63,7 +63,7 @@ pub struct SlotName(#[get(method = "name")] String);
 
 #[derive(Clone, Debug, PartialEq, Eq, Get)]
 pub struct Slot {
-    slot: SlotName,
+    slot: Option<SlotName>,
     sub: Option<SlotName>,
     operator: Option<SlotOperator>,
 }

src/atom/parsers.rs

@@ -112,7 +112,7 @@ pub fn slotname<'a>() -> impl Parser<&'a str, Output = SlotName> {
 }
 
 pub fn slot<'a>() -> impl Parser<&'a str, Output = Slot> {
-    slotname()
+    opt(slotname())
         .and(opt(slotname().preceded_by(tag("/"))))
         .and(opt(slot_operator()))
         .map(|((slot, sub), operator)| Slot {
@@ -273,4 +273,11 @@ mod test {
 
         assert!(atom().check_finished(it).is_err())
     }
+
+    #[test]
+    fn test_empty_slot() {
+        let it = InputIter::new("foo/bar-1.0.0:=");
+
+        atom().check_finished(it).unwrap();
+    }
 }