feat: in MainPodBuilder track literal contains in dict_contains (#456)

The MainPodBuilder automatically adds contains statements for operations
that are created from entries.  But if the contains statement was
already added manually there will be duplicates.  We now track manually
added contains statements so that we don't generate duplicates when
adding statements from entries that use them.

src/frontend/mod.rs

@@ -131,7 +131,6 @@ pub struct MainPodBuilder {
     pub operations: Vec<Operation>,
     pub public_statements: Vec<Statement>,
     // Internal state
-    // TODO: track contains ops with literals added explicitly as well.
     dict_contains: Vec<(Value, Value)>, // (root, key)
 }
 
@@ -177,6 +176,19 @@ impl MainPodBuilder {
     pub fn insert(&mut self, public: bool, st_op: (Statement, Operation)) -> Result<()> {
         // TODO: Do error handling instead of panic
         let (st, op) = st_op;
+
+        // If we're adding a Contains statement with literal arguments (an Entry), track it in
+        // `dict_contains` to avoid adding it again via `Self::add_entries_contains`.
+        if let Statement::Contains(
+            ValueRef::Literal(dict),
+            ValueRef::Literal(key),
+            ValueRef::Literal(_),
+        ) = &st
+        {
+            let root_key = (dict.clone(), key.clone());
+            self.dict_contains.push(root_key);
+        }
+
         if public {
             self.public_statements.push(st.clone());
         }