test: tuple variants reject extra elements from text and every Value

Author: claude

src/tests/serde.rs

@@ -1371,3 +1371,36 @@ fn fixed_length_sequences_reject_extra_elements() {
     let mut d = b"[1]".to_vec();
     assert!(from_slice::<(u8, u8)>(&mut d).is_err());
 }
+
+#[test]
+fn tuple_variants_reject_extra_elements() {
+    // A tuple variant's array is a fixed-length sequence too, from text and from every Value.
+    use crate::serde::{
+        from_borrowed_value, from_owned_value, from_refborrowed_value, from_refowned_value,
+    };
+    #[derive(Deserialize, Debug, PartialEq)]
+    enum Enm {
+        Var(u8, u8),
+    }
+    let mut d = br#"{"Var":[1,2,3]}"#.to_vec();
+    assert!(from_slice::<Enm>(&mut d).is_err());
+    let mut d = br#"[{"Var":[1,2,3]},{"Var":[4,5]}]"#.to_vec();
+    assert!(from_slice::<Vec<Enm>>(&mut d).is_err());
+
+    let mut d = br#"{"Var":[1,2,3]}"#.to_vec();
+    let o = to_owned_value(&mut d).expect("valid");
+    let mut d2 = br#"{"Var":[1,2,3]}"#.to_vec();
+    let b = to_borrowed_value(&mut d2).expect("valid");
+    assert!(from_owned_value::<Enm>(o.clone()).is_err());
+    assert!(from_refowned_value::<Enm>(&o).is_err());
+    assert!(from_borrowed_value::<Enm>(b.clone()).is_err());
+    assert!(from_refborrowed_value::<Enm>(&b).is_err());
+
+    // exact length is unchanged
+    let mut d = br#"{"Var":[1,2]}"#.to_vec();
+    assert_eq!(from_slice::<Enm>(&mut d).ok(), Some(Enm::Var(1, 2)));
+    let mut d = br#"{"Var":[1,2]}"#.to_vec();
+    let o = to_owned_value(&mut d).expect("valid");
+    assert_eq!(from_refowned_value::<Enm>(&o).ok(), Some(Enm::Var(1, 2)));
+    assert_eq!(from_owned_value::<Enm>(o).ok(), Some(Enm::Var(1, 2)));
+}