fix cycles in when traversing graph

src/fromager/dependency_graph.py

@@ -240,6 +240,7 @@ def get_dependency_edges(
         visited = set()
         for edge in self._depth_first_traversal(
             self.nodes[ROOT].children,
+            set(),
             match_dep_types=match_dep_types,
         ):
             if edge.destination_node.key not in visited:
@@ -277,13 +278,17 @@ def get_install_dependency_versions(
 
     def _depth_first_traversal(
         self,
-        start_node: list[DependencyEdge],
+        start_edges: list[DependencyEdge],
+        visited: set[str],
         match_dep_types: list[RequirementType] | None = None,
     ) -> typing.Iterable[DependencyEdge]:
-        for edge in start_node:
+        for edge in start_edges:
+            if edge.destination_node.key in visited:
+                continue
             if match_dep_types and edge.req_type not in match_dep_types:
                 continue
+            visited.add(edge.destination_node.key)
             yield edge
             yield from self._depth_first_traversal(
-                edge.destination_node.children, match_dep_types
+                edge.destination_node.children, visited, match_dep_types
             )

tests/test_graph.py

@@ -143,3 +143,41 @@ def test_get_install_dependencies():
         for node in graph.get_install_dependencies()
     ]
     assert install_nodes == ["a==2.0", "d==6.0", "b==3.0", "e==6.0"]
+
+
+def test_cycles_get_install_dependencies():
+    graph = dependency_graph.DependencyGraph.from_dict(raw_graph)
+    # create cycle: a depends on d and d depends on a
+    graph.add_dependency(
+        parent_name=canonicalize_name("a"),
+        parent_version=Version("2.0"),
+        req_type=requirements_file.RequirementType.INSTALL,
+        req=Requirement("d>=4.0"),
+        req_version=Version("6.0"),
+        download_url="url for d",
+    )
+
+    graph.add_dependency(
+        parent_name=canonicalize_name("d"),
+        parent_version=Version("6.0"),
+        req_type=requirements_file.RequirementType.INSTALL,
+        req=Requirement("a<=2.0"),
+        req_version=Version("2.0"),
+        download_url="url for a",
+    )
+
+    # add another duplicate toplevel
+    graph.add_dependency(
+        parent_name=None,
+        parent_version=None,
+        req_type=requirements_file.RequirementType.TOP_LEVEL,
+        req=Requirement("a<=2.0"),
+        req_version=Version("2.0"),
+        download_url="url for a",
+    )
+
+    install_nodes = [
+        f"{node.to_dict()['canonicalized_name']}=={node.to_dict()['version']}"
+        for node in graph.get_install_dependencies()
+    ]
+    assert install_nodes == ["a==2.0", "d==6.0"]