Duplicates in sets is now an Error.

Clojure's behavior:
(clojure.edn/read-string "#{1 2 2 3}")
java.lang.IllegalArgumentException: Duplicate key: 2 [at <repl>:1:1]

src/deserialize/parse.rs

@@ -262,9 +262,14 @@ fn parse_set(walker: &mut Walker<'_>) -> Result<Edn, Error> {
             }
             Some(_) => {
                 let next = parse_internal(walker)?;
-                if next != Edn::Empty {
-                    set.insert(next);
-                }
+                if next != Edn::Empty && !set.insert(next) {
+                    return Err(Error {
+                        code: Code::SetDuplicateKey,
+                        line: Some(walker.line),
+                        column: Some(walker.column),
+                        ptr: Some(walker.ptr),
+                    });
+                };
             }
             _ => {
                 return Err(Error {

src/edn/error.rs

@@ -20,6 +20,7 @@ pub enum Code {
 
     /// Parse errors
     HashMapDuplicateKey,
+    SetDuplicateKey,
     InvalidChar,
     InvalidEscape,
     InvalidKeyword,

tests/error_messages.rs

@@ -94,4 +94,21 @@ world!"#
         let small = edn_rs::from_edn::<u8>(&Edn::UInt(9876123));
         assert_eq!(format!("{small:?}"), "Err(EdnError { code: TryFromInt(TryFromIntError(())), line: None, column: None, ptr: None })");
     }
+
+    #[test]
+    #[cfg(feature = "sets")]
+    fn duplicate_in_set() {
+        assert_eq!(
+            err_as_string("#{1 42 42 3}"),
+            "EdnError { code: SetDuplicateKey, line: Some(1), column: Some(10), ptr: Some(9) }"
+        );
+    }
+
+    #[test]
+    fn duplicate_in_map() {
+        assert_eq!(
+            err_as_string("{:foo 42 :bar 43 :foo \"cat\"}"),
+            "EdnError { code: HashMapDuplicateKey, line: Some(1), column: Some(28), ptr: Some(27) }"
+        );
+    }
 }