fix(codegen): Allow multiple paths for a shape (#755)

Author: RitvikKapila

codegen/smithy-dafny-codegen/src/main/java/software/amazon/polymorph/utils/ModelUtils.java

@@ -461,7 +461,6 @@ public static Set<List<ShapeId>> findAllDependentShapesWithPaths(
     Set<List<ShapeId>> pathsToShapes = new LinkedHashSet<>(
       new LinkedHashSet<>()
     );
-    Set<ShapeId> visited = new HashSet<>();
 
     // Breadth-first search via getDependencyShapeIds
     final Queue<List<ShapeId>> toTraverse = new LinkedList<>(
@@ -470,16 +469,16 @@ public static Set<List<ShapeId>> findAllDependentShapesWithPaths(
     while (!toTraverse.isEmpty()) {
       final List<ShapeId> currentShapeIdWithPath = toTraverse.remove();
 
-      // to avoid cycles, only keep the first list with a given last element
-      ShapeId last = currentShapeIdWithPath.get(
-        currentShapeIdWithPath.size() - 1
-      );
-      if (visited.add(last) && pathsToShapes.add(currentShapeIdWithPath)) {
+      if (pathsToShapes.add(currentShapeIdWithPath)) {
         final Shape currentShape = model.expectShape(
           currentShapeIdWithPath.get(currentShapeIdWithPath.size() - 1)
         );
         final List<List<ShapeId>> dependencyShapeIdsWithPaths =
           getDependencyShapeIds(currentShape)
+            // to avoid cycles, append only those dependencyShapeId which are not already in the path currentShapeIdWithPath
+            .filter(dependencyShapeId ->
+              !currentShapeIdWithPath.contains(dependencyShapeId)
+            )
             .map(dependencyShapeId ->
               Stream
                 .concat(