From a79e365e5782f9b41e0d5f701cce9196a74afda5 Mon Sep 17 00:00:00 2001
From: J2ObjC Team <j2objc-copybara@google.com>
Date: Fri, 14 Aug 2026 17:11:47 -0700
Subject: [PATCH] Fix infinite loops in cycle finder.

This change fixes several infinite loop conditions in cycle finder:
1. Adds loop detection in GraphBuilder.addSuperclassEdges to prevent infinite loops when type hierarchies have cycles.
2. Fixes ReferenceGraph.findShortestCycle to terminate if there are no more nodes to visit, returning an empty list.
3. Fixes CycleFinder.handleStronglyConnectedComponent to skip cycle extraction and remove the root from unused types if findShortestCycle returns an empty list.

PiperOrigin-RevId: 964969489
---
 .../java/com/google/devtools/cyclefinder/CycleFinder.java     | 4 ++++
 .../java/com/google/devtools/cyclefinder/GraphBuilder.java    | 3 ++-
 .../java/com/google/devtools/cyclefinder/ReferenceGraph.java  | 3 +++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/cycle_finder/src/main/java/com/google/devtools/cyclefinder/CycleFinder.java b/cycle_finder/src/main/java/com/google/devtools/cyclefinder/CycleFinder.java
index ca8c5e7018..efda08cfd1 100644
--- a/cycle_finder/src/main/java/com/google/devtools/cyclefinder/CycleFinder.java
+++ b/cycle_finder/src/main/java/com/google/devtools/cyclefinder/CycleFinder.java
@@ -220,6 +220,10 @@ private void handleStronglyConnectedComponent(ReferenceGraph subgraph) {
       TypeNode root = Iterables.getFirst(unusedTypes, null);
       assert root != null;
       List<Edge> cycle = subgraph.findShortestCycle(root);
+      if (cycle.isEmpty()) {
+        unusedTypes.remove(root);
+        continue;
+      }
       if (shouldAddCycle(cycle)) {
         cycles.add(cycle);
       }
diff --git a/cycle_finder/src/main/java/com/google/devtools/cyclefinder/GraphBuilder.java b/cycle_finder/src/main/java/com/google/devtools/cyclefinder/GraphBuilder.java
index f6c15d62b1..673a2ec297 100644
--- a/cycle_finder/src/main/java/com/google/devtools/cyclefinder/GraphBuilder.java
+++ b/cycle_finder/src/main/java/com/google/devtools/cyclefinder/GraphBuilder.java
@@ -135,8 +135,9 @@ private void addSubtypeEdges() {
 
   private void addSuperclassEdges() {
     for (TypeNode type : allTypes.values()) {
+      Set<TypeNode> visited = new HashSet<>();
       TypeNode superclassNode = superclasses.get(type);
-      while (superclassNode != null) {
+      while (superclassNode != null && visited.add(superclassNode)) {
         for (Edge e : graph.getEdges(superclassNode)) {
           addEdge(Edge.newSuperclassEdge(e, type, superclassNode));
         }
diff --git a/cycle_finder/src/main/java/com/google/devtools/cyclefinder/ReferenceGraph.java b/cycle_finder/src/main/java/com/google/devtools/cyclefinder/ReferenceGraph.java
index f05d496efa..55b03b8111 100644
--- a/cycle_finder/src/main/java/com/google/devtools/cyclefinder/ReferenceGraph.java
+++ b/cycle_finder/src/main/java/com/google/devtools/cyclefinder/ReferenceGraph.java
@@ -67,6 +67,9 @@ public List<Edge> findShortestCycle(TypeNode root) {
     Set<TypeNode> visited = new HashSet<>();
     List<TypeNode> toVisit = Lists.newArrayList(root);
     outer: while (true) {
+      if (toVisit.isEmpty()) {
+        return Collections.emptyList();
+      }
       List<TypeNode> visitNext = new ArrayList<>();
       for (TypeNode source : toVisit) {
         visited.add(source);