Allow borrow for field identifiers

test_suite/tests/test_borrow.rs

@@ -90,6 +90,37 @@ fn test_struct() {
     );
 }
 
+#[test]
+fn test_field_identifier() {
+    #[derive(Deserialize, Debug, PartialEq)]
+    #[serde(field_identifier)]
+    enum FieldStr<'a> {
+        #[serde(borrow)]
+        Str(&'a str),
+    }
+
+    assert_de_tokens(
+        &FieldStr::Str("value"),
+        &[
+            Token::BorrowedStr("value"),
+        ],
+    );
+
+    #[derive(Deserialize, Debug, PartialEq)]
+    #[serde(field_identifier)]
+    enum FieldBytes<'a> {
+        #[serde(borrow)]
+        Bytes(&'a [u8]),
+    }
+
+    assert_de_tokens(
+        &FieldBytes::Bytes(b"value"),
+        &[
+            Token::BorrowedBytes(b"value"),
+        ],
+    );
+}
+
 #[test]
 fn test_cow() {
     #[derive(Deserialize)]