Add helper function for traversal direction

src/dag_algo/mod.rs

@@ -34,6 +34,18 @@ use petgraph::graph::NodeIndex;
 use petgraph::prelude::*;
 use petgraph::visit::NodeCount;
 
+/// Return a pair of [`petgraph::Direction`] values corresponding to the "forwards" and "backwards"
+/// direction of graph traversal, based on whether the graph is being traved forwards (following
+/// the edges) or backward (reversing along edges).  The order of returns is (forwards, backwards).
+#[inline(always)]
+pub fn traversal_directions(reverse: bool) -> (petgraph::Direction, petgraph::Direction) {
+    if reverse {
+        (petgraph::Direction::Outgoing, petgraph::Direction::Incoming)
+    } else {
+        (petgraph::Direction::Incoming, petgraph::Direction::Outgoing)
+    }
+}
+
 /// Find the longest path in a DAG
 ///
 /// :param PyDiGraph graph: The graph to find the longest path on. The input
@@ -374,11 +386,7 @@ pub fn lexicographical_topological_sort(
     };
     // HashMap of node_index indegree
     let node_count = dag.node_count();
-    let (in_dir, out_dir) = if reverse {
-        (petgraph::Direction::Outgoing, petgraph::Direction::Incoming)
-    } else {
-        (petgraph::Direction::Incoming, petgraph::Direction::Outgoing)
-    };
+    let (in_dir, out_dir) = traversal_directions(reverse);
     let mut in_degree_map: HashMap<NodeIndex, usize> = HashMap::with_capacity(node_count);
     for node in dag.graph.node_indices() {
         in_degree_map.insert(node, dag.graph.edges_directed(node, in_dir).count());

src/toposort.rs

@@ -22,7 +22,7 @@ use pyo3::Python;
 use petgraph::stable_graph::NodeIndex;
 use petgraph::visit::IntoNodeIdentifiers;
 
-use crate::dag_algo::is_directed_acyclic_graph;
+use crate::dag_algo::{is_directed_acyclic_graph, traversal_directions};
 use crate::DAGHasCycle;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -88,12 +88,7 @@ impl TopologicalSorter {
             }
         }
 
-        let in_dir = if reverse {
-            petgraph::Direction::Outgoing
-        } else {
-            petgraph::Direction::Incoming
-        };
-
+        let (in_dir, _) = traversal_directions(reverse);
         let ready_nodes = {
             let dag = &dag.borrow(py);
 
@@ -156,11 +151,7 @@ impl TopologicalSorter {
     ///     by "get_ready".
     fn done(&mut self, py: Python, nodes: Vec<usize>) -> PyResult<()> {
         let dag = &self.dag.borrow(py);
-        let (in_dir, out_dir) = if self.reverse {
-            (petgraph::Direction::Outgoing, petgraph::Direction::Incoming)
-        } else {
-            (petgraph::Direction::Incoming, petgraph::Direction::Outgoing)
-        };
+        let (in_dir, out_dir) = traversal_directions(self.reverse);
         for node in nodes {
             let node = NodeIndex::new(node);
             match self.node2state.get_mut(&node) {