Add regression test for issue 1969

test_suite/tests/test_gen.rs

@@ -7,6 +7,7 @@
 #![allow(
     unknown_lints,
     mixed_script_confusables,
+    clippy::ptr_arg,
     clippy::trivially_copy_pass_by_ref
 )]
 
@@ -735,6 +736,12 @@ fn test_gen() {
         #[serde(borrow = "'a")]
         f: mac!(Cow<'a, str>),
     }
+
+    #[derive(Serialize)]
+    struct Struct {
+        #[serde(serialize_with = "vec_first_element")]
+        vec: Vec<Self>,
+    }
 }
 
 //////////////////////////////////////////////////////////////////////////
@@ -808,3 +815,11 @@ where
 pub fn is_zero(n: &u8) -> bool {
     *n == 0
 }
+
+fn vec_first_element<T, S>(vec: &Vec<T>, serializer: S) -> StdResult<S::Ok, S::Error>
+where
+    T: Serialize,
+    S: Serializer,
+{
+    vec.first().serialize(serializer)
+}