fix(#4645): shortestPath edge:true ClassCastException + wrong vertex in BOTH direction

docs/4645-shortestpath-edge-both-classcastexception.md

@@ -0,0 +1,33 @@
+# Fix #4645 - shortestPath edge:true ClassCastException on BOTH direction with empty side
+
+## Issue
+
+`shortestPath(..., {'direction':'BOTH','edge':true})` throws `ClassCastException` when one of the two directional sub-queries returns an empty edge list.
+
+## Root Cause (two bugs)
+
+**Bug 1 - ClassCastException:** `EdgeToVertexIterable.iterator()` unconditionally cast the result of `edges.iterator()` to `EdgeIterator`:
+```java
+return new EdgeToVertexIterator((EdgeIterator) edges.iterator(), direction);
+```
+When `direction:BOTH`, `SQLFunctionShortestPath.getVerticesAndEdges()` recurses into `OUT` and `IN`. For a vertex that has only an outgoing edge, the `IN` side returns `GraphEngine.EMPTY_EDGE_LIST`. That list's `iterator()` returns `Collections.emptyIterator()` which is NOT an `EdgeIterator`, causing `ClassCastException`.
+
+**Bug 2 - Wrong vertex returned:** `EdgeToVertexIterator.next()` called `edge.getVertex(direction)` where `direction` is the traversal direction. For an OUT traversal from vertex 'a', this returns 'a' (the OUT/source end) rather than the neighbor 'b' (the IN/destination end). The BFS made no progress because every "neighbor" was the current vertex itself.
+
+## Fix
+
+**EdgeToVertexIterable:** check `instanceof ResettableIterator` (the common supertype of `EdgeIterator` and `EdgeIteratorFilter`) before casting. `EMPTY_EDGE_LIST.iterator()` returns `Collections.emptyIterator()` which is not a `ResettableIterator`, so it returns an empty iterator instead.
+
+**EdgeToVertexIterator:** change field type to `ResettableIterator<Edge>` and fix `next()` to use the opposite direction (`direction == OUT ? IN : OUT`), which correctly returns the neighbor vertex.
+
+## Files Changed
+
+- `engine/src/main/java/com/arcadedb/graph/EdgeToVertexIterable.java` - guard against non-ResettableIterator (empty edge list)
+- `engine/src/main/java/com/arcadedb/graph/EdgeToVertexIterator.java` - accept `ResettableIterator<Edge>`; fix `next()` to return the opposite-end vertex
+- `engine/src/test/java/com/arcadedb/function/sql/graph/SQLFunctionShortestPathTest.java` - regression test for `edge:true` + `direction:BOTH` with asymmetric edges
+
+## Verification
+
+Run: `mvn test -pl engine -Dtest=SQLFunctionShortestPathTest`
+
+Results: 12 tests run, 0 failures, 0 errors.

engine/src/main/java/com/arcadedb/graph/EdgeToVertexIterable.java

@@ -18,6 +18,9 @@
  */
 package com.arcadedb.graph;
 
+import com.arcadedb.utility.ResettableIterator;
+
+import java.util.Collections;
 import java.util.Iterator;
 
 /**
@@ -34,6 +37,9 @@ public EdgeToVertexIterable(final Iterable<Edge> edges, final Vertex.DIRECTION d
 
   @Override
   public Iterator<Vertex> iterator() {
-    return new EdgeToVertexIterator((EdgeIterator) edges.iterator(), direction);
+    final Iterator<Edge> iter = edges.iterator();
+    if (!(iter instanceof ResettableIterator))
+      return Collections.emptyIterator();
+    return new EdgeToVertexIterator((ResettableIterator<Edge>) iter, direction);
   }
 }

engine/src/main/java/com/arcadedb/graph/EdgeToVertexIterator.java

@@ -24,10 +24,10 @@
  * Created by luigidellaquila on 02/07/16.
  */
 public class EdgeToVertexIterator implements ResettableIterator<Vertex> {
-  private final EdgeIterator     edgeIterator;
-  private final Vertex.DIRECTION direction;
+  private final ResettableIterator<Edge> edgeIterator;
+  private final Vertex.DIRECTION         direction;
 
-  public EdgeToVertexIterator(final EdgeIterator iterator, final Vertex.DIRECTION direction) {
+  public EdgeToVertexIterator(final ResettableIterator<Edge> iterator, final Vertex.DIRECTION direction) {
     if (direction == Vertex.DIRECTION.BOTH)
       throw new IllegalArgumentException("edge to vertex iterator does not support BOTH as direction");
 
@@ -42,7 +42,7 @@ public boolean hasNext() {
 
   @Override
   public Vertex next() {
-    return edgeIterator.next().getVertex(direction);
+    return edgeIterator.next().getVertex(direction == Vertex.DIRECTION.OUT ? Vertex.DIRECTION.IN : Vertex.DIRECTION.OUT);
   }
 
   @Override

engine/src/test/java/com/arcadedb/function/sql/graph/SQLFunctionShortestPathTest.java

@@ -203,6 +203,36 @@ void consolidatedOptionsMap() throws Exception {
     });
   }
 
+  @Test
+  void edgeTrueDirectionBothWithAsymmetricEdges() throws Exception {
+    TestHelper.executeInNewDatabase("testEdgeBothAsymmetric", graph -> {
+      final MutableVertex[] verts = new MutableVertex[2];
+
+      graph.transaction(() -> {
+        graph.getSchema().createVertexType("BugSP_V");
+        graph.getSchema().createEdgeType("BugSP_E");
+
+        verts[0] = graph.newVertex("BugSP_V").set("name", "a").save();
+        verts[1] = graph.newVertex("BugSP_V").set("name", "b").save();
+        verts[0].newEdge("BugSP_E", verts[1]);
+      });
+
+      function = new SQLFunctionShortestPath();
+
+      final Map<String, Object> options = new HashMap<>();
+      options.put("direction", "BOTH");
+      options.put("edge", true);
+
+      final List<RID> result = function.execute(null, null, null, new Object[] { verts[0], verts[1], options },
+          new BasicCommandContext());
+
+      // expected: [a-rid, edge-rid, b-rid]
+      assertThat(result).hasSize(3);
+      assertThat(result.getFirst()).isEqualTo(verts[0].getIdentity());
+      assertThat(result.getLast()).isEqualTo(verts[1].getIdentity());
+    });
+  }
+
   @Test
   void rejectsUnknownOption() throws Exception {
     TestHelper.executeInNewDatabase("testShortestPathUnknownOption", graph -> {