From 5c82736c7a86262ff5edccab1421976123293bdc Mon Sep 17 00:00:00 2001
From: Miles Johnson <mileswjohnson@gmail.com>
Date: Wed, 4 Oct 2023 16:35:44 -0700
Subject: [PATCH] Add cycle stuff.

---
 nextgen/action-graph/src/action_graph.rs      | 31 +++++++------------
 .../action-graph/tests/action_graph_test.rs   | 25 +++++++++++++++
 nextgen/project-graph/src/project_graph.rs    |  9 ++++++
 3 files changed, 45 insertions(+), 20 deletions(-)

diff --git a/nextgen/action-graph/src/action_graph.rs b/nextgen/action-graph/src/action_graph.rs
index 9fc70e3a77c..7cb832ab873 100644
--- a/nextgen/action-graph/src/action_graph.rs
+++ b/nextgen/action-graph/src/action_graph.rs
@@ -30,7 +30,7 @@ impl ActionGraph {
     }
 
     pub fn reset_iterator(&mut self) -> miette::Result<()> {
-        // self.detect_cycle()?;
+        self.detect_cycle()?;
 
         self.queue.clear();
         self.visited.clear();
@@ -104,27 +104,18 @@ impl ActionGraph {
     }
 
     fn detect_cycle(&self) -> miette::Result<()> {
-        if self.is_empty() || self.get_node_count() == 1 {
-            return Ok(());
+        if self.get_node_count() > 1 {
+            if let Err(cycle) = petgraph::algo::toposort(&self.graph, None) {
+                return Err(ActionGraphError::CycleDetected(
+                    self.get_node_from_index(&cycle.node_id())
+                        .map(|n| n.label())
+                        .unwrap_or_else(|| "(unknown)".into()),
+                )
+                .into());
+            }
         }
 
-        let scc = petgraph::algo::kosaraju_scc(&self.graph);
-
-        // TODO
-        dbg!(&scc);
-
-        // The cycle is always the last sequence in the list
-        let Some(cycle) = scc.last() else {
-            return Err(ActionGraphError::CycleDetected("(unknown)".into()).into());
-        };
-
-        let path = cycle
-            .iter()
-            .filter_map(|i| self.get_node_from_index(i).map(|n| n.label()))
-            .collect::<Vec<String>>()
-            .join(" → ");
-
-        Err(ActionGraphError::CycleDetected(path).into())
+        Ok(())
     }
 }
 
diff --git a/nextgen/action-graph/tests/action_graph_test.rs b/nextgen/action-graph/tests/action_graph_test.rs
index 987bc415fd0..de9a843f356 100644
--- a/nextgen/action-graph/tests/action_graph_test.rs
+++ b/nextgen/action-graph/tests/action_graph_test.rs
@@ -174,6 +174,31 @@ fn topo(mut graph: ActionGraph) -> Vec<ActionNode> {
 mod action_graph {
     use super::*;
 
+    // #[test]
+    // fn errors_on_cycle() {
+    //     let mut graph = ProjectGraphType::new();
+    //     let a = graph.add_node(create_project("a"));
+    //     let b = graph.add_node(create_project("b"));
+    //     graph.add_edge(a, b, DependencyScope::Build);
+    //     graph.add_edge(b, a, DependencyScope::Build);
+
+    //     let pg = ProjectGraph::new(
+    //         graph,
+    //         FxHashMap::from_iter([
+    //             ("a".into(), ProjectNode::new(0)),
+    //             ("b".into(), ProjectNode::new(1)),
+    //         ]),
+    //         &PathBuf::from("."),
+    //     );
+
+    //     let mut builder = ActionGraphBuilder::new(&pg).unwrap();
+
+    //     builder.sync_project(&pg.get("a").unwrap()).unwrap();
+    //     builder.sync_project(&pg.get("b").unwrap()).unwrap();
+
+    //     builder.build().unwrap().reset_iterator().unwrap();
+    // }
+
     mod install_deps {
         use super::*;
 
diff --git a/nextgen/project-graph/src/project_graph.rs b/nextgen/project-graph/src/project_graph.rs
index 012de71483a..38b15e90294 100644
--- a/nextgen/project-graph/src/project_graph.rs
+++ b/nextgen/project-graph/src/project_graph.rs
@@ -34,6 +34,15 @@ pub struct ProjectNode {
     pub source: WorkspaceRelativePathBuf,
 }
 
+impl ProjectNode {
+    pub fn new(index: usize) -> Self {
+        ProjectNode {
+            index: NodeIndex::new(index),
+            ..ProjectNode::default()
+        }
+    }
+}
+
 #[derive(Default)]
 pub struct ProjectGraph {
     pub check_boundaries: bool,