caliperreader: handle root nodes in _create_parent (#68)

When creating parent nodes, we need to handle the case that the parent might be
a root node. Previously, the recursive _create_parent calls were being made on
root nodes, and we incorrectly tried to index into the grandparent callpath
tuple, even though it was empty. This ends the recursion if we encounter an
empty callpath tuple.

hatchet/readers/caliper_native_reader.py

@@ -114,6 +114,8 @@ def read_metrics(self, ctx="path"):
         return df_metrics
 
     def create_graph(self, ctx="path"):
+        list_roots = []
+
         def _create_parent(child_node, parent_callpath):
             """We may encounter a parent node in the callpath before we see it
             as a child node. In this case, we need to create a hatchet node for
@@ -131,27 +133,46 @@ def _create_parent(child_node, parent_callpath):
                 return
             else:
                 # else create the parent and add parent/child
-                grandparent_callpath = parent_callpath[:-1]
-                parent_name = parent_callpath[-1]
-
-                parent_node = Node(
-                    Frame({"type": "function", "name": parent_name}), None
-                )
-
-                self.callpath_to_node[parent_callpath] = parent_node
-                self.callpath_to_idx[parent_callpath] = self.global_nid
 
-                node_dict = dict(
-                    {"name": parent_name, "node": parent_node, "nid": self.global_nid},
-                )
-                self.idx_to_node[self.global_nid] = node_dict
-                self.global_nid += 1
+                # if root node, end recursive call to create parent nodes
+                if not parent_callpath:
+                    list_roots.append(child_node)
+
+                    node_dict = dict(
+                        {
+                            "name": child_node.frame["name"],
+                            "node": child_node,
+                            "nid": self.global_nid,
+                        }
+                    )
+
+                    self.idx_to_node[self.global_nid] = node_dict
+                    self.global_nid += 1
+                else:
+                    grandparent_callpath = parent_callpath[:-1]
+                    parent_name = parent_callpath[-1]
+
+                    parent_node = Node(
+                        Frame({"type": "function", "name": parent_name}), None
+                    )
+
+                    self.callpath_to_node[parent_callpath] = parent_node
+                    self.callpath_to_idx[parent_callpath] = self.global_nid
+
+                    node_dict = dict(
+                        {
+                            "name": parent_name,
+                            "node": parent_node,
+                            "nid": self.global_nid,
+                        },
+                    )
+                    self.idx_to_node[self.global_nid] = node_dict
+                    self.global_nid += 1
+
+                    parent_node.add_child(child_node)
+                    child_node.add_parent(parent_node)
+                    _create_parent(parent_node, grandparent_callpath)
 
-                parent_node.add_child(child_node)
-                child_node.add_parent(parent_node)
-                _create_parent(parent_node, grandparent_callpath)
-
-        list_roots = []
         parent_hnode = None
         records = self.filename_or_caliperreader.records