Fix Arrays with leading nulls

pgrx-tests/src/tests/array_tests.rs

@@ -482,4 +482,52 @@ mod tests {
         }
         Ok(())
     }
+
+    #[pg_test]
+    fn test_text_array_as_vec_string() -> Result<(), Box<dyn std::error::Error>> {
+        let a = Spi::get_one::<Array<String>>(
+            "SELECT ARRAY[NULL, NULL, NULL, NULL, 'the fifth element']::text[]",
+        )?
+        .expect("spi result was NULL")
+        .into_iter()
+        .collect::<Vec<_>>();
+        assert_eq!(a, vec![None, None, None, None, Some(String::from("the fifth element"))]);
+        Ok(())
+    }
+
+    #[pg_test]
+    fn test_text_array_iter() -> Result<(), Box<dyn std::error::Error>> {
+        let a = Spi::get_one::<Array<String>>(
+            "SELECT ARRAY[NULL, NULL, NULL, NULL, 'the fifth element']::text[]",
+        )?
+        .expect("spi result was NULL");
+
+        let mut iter = a.iter();
+
+        assert_eq!(iter.next(), Some(None));
+        assert_eq!(iter.next(), Some(None));
+        assert_eq!(iter.next(), Some(None));
+        assert_eq!(iter.next(), Some(None));
+        assert_eq!(iter.next(), Some(Some(String::from("the fifth element"))));
+        assert_eq!(iter.next(), None);
+
+        Ok(())
+    }
+
+    #[pg_test]
+    fn test_text_array_via_getter() -> Result<(), Box<dyn std::error::Error>> {
+        let a = Spi::get_one::<Array<String>>(
+            "SELECT ARRAY[NULL, NULL, NULL, NULL, 'the fifth element']::text[]",
+        )?
+        .expect("spi result was NULL");
+
+        assert_eq!(a.get(0), Some(None));
+        assert_eq!(a.get(1), Some(None));
+        assert_eq!(a.get(2), Some(None));
+        assert_eq!(a.get(3), Some(None));
+        assert_eq!(a.get(4), Some(Some(String::from("the fifth element"))));
+        assert_eq!(a.get(5), None);
+
+        Ok(())
+    }
 }

pgrx/src/datum/array.rs

@@ -626,9 +626,13 @@ impl<'a, T: FromDatum> Iterator for ArrayIterator<'a, T> {
     fn next(&mut self) -> Option<Self::Item> {
         let Self { array, curr, ptr } = self;
         let Some(is_null) = array.null_slice.get(*curr) else { return None };
-        let element = unsafe { array.bring_it_back_now(*ptr, is_null) };
         *curr += 1;
-        if let Some(false) = array.null_slice.get(*curr) {
+
+        let element = unsafe { array.bring_it_back_now(*ptr, is_null) };
+        if !is_null {
+            // SAFETY: This has to not move for nulls, as they occupy 0 data bytes,
+            // and it has to move only after unpacking a non-null varlena element,
+            // as the iterator starts by pointing to the first non-null element!
             *ptr = unsafe { array.one_hop_this_time(*ptr) };
         }
         Some(element)
@@ -679,9 +683,13 @@ impl<'a, T: FromDatum> Iterator for ArrayIntoIterator<'a, T> {
     fn next(&mut self) -> Option<Self::Item> {
         let Self { array, curr, ptr } = self;
         let Some(is_null) = array.null_slice.get(*curr) else { return None };
-        let element = unsafe { array.bring_it_back_now(*ptr, is_null) };
         *curr += 1;
-        if let Some(false) = array.null_slice.get(*curr) {
+
+        let element = unsafe { array.bring_it_back_now(*ptr, is_null) };
+        if !is_null {
+            // SAFETY: This has to not move for nulls, as they occupy 0 data bytes,
+            // and it has to move only after unpacking a non-null varlena element,
+            // as the iterator starts by pointing to the first non-null element!
             *ptr = unsafe { array.one_hop_this_time(*ptr) };
         }
         Some(element)