row_labels.is_null() actually refers to a method checking for a null pointer (#710)

* `row_labels.is_null()` actually refers to a method checking for a null pointer.

* Add a regression test

* Implement `is_null` for RObject

Author: dfalbel

crates/ark/tests/data_explorer.rs

@@ -1877,6 +1877,12 @@ fn test_row_names_matrix() {
         }),
         format_options: default_format_options(),
     });
+    assert_match!(socket_rpc(&socket, DataExplorerBackendRequest::GetState),
+        DataExplorerBackendReply::GetStateReply(state) => {
+            assert_eq!(state.has_row_labels, true)
+        }
+    );
+
     assert_match!(socket_rpc(&socket, req),
         DataExplorerBackendReply::GetRowLabelsReply(row_labels) => {
             let labels = row_labels.row_labels;
@@ -1885,4 +1891,14 @@ fn test_row_names_matrix() {
             assert_eq!(labels[0][2], "Merc 240D");
         }
     );
+
+    // Convert mtcars to a matrix
+    let socket =
+        open_data_explorer_from_expression("matrix(0, ncol =10, nrow = 10)", Some("zero_matrix"))
+            .unwrap();
+    assert_match!(socket_rpc(&socket, DataExplorerBackendRequest::GetState),
+        DataExplorerBackendReply::GetStateReply(state) => {
+            assert_eq!(state.has_row_labels, false)
+        }
+    );
 }

crates/harp/src/object.rs

@@ -352,6 +352,10 @@ impl RObject {
         r_is_object(self.sexp)
     }
 
+    pub fn is_null(&self) -> bool {
+        r_is_null(self.sexp)
+    }
+
     pub fn size(&self) -> harp::Result<usize> {
         r_size(self.sexp)
     }
@@ -1154,6 +1158,7 @@ mod tests {
     use stdext::assert_match;
 
     use super::*;
+    use crate::parse_eval_global;
     use crate::r_char;
 
     #[test]
@@ -1729,4 +1734,15 @@ mod tests {
             assert_eq!(items_in, items_out);
         })
     }
+
+    #[test]
+    fn test_is_null() {
+        crate::r_task(|| {
+            let x = parse_eval_global("NULL").unwrap();
+            assert!(x.is_null());
+
+            let x = parse_eval_global("1").unwrap();
+            assert!(!x.is_null());
+        })
+    }
 }