From ae314cce9301afb47646fe59a957fe602205a1b4 Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Wed, 1 Apr 2026 19:59:59 -0700
Subject: [PATCH] [ILibraryView] child_order shouldn't leak
 graphlib.CycleErrror

---
 masque/library.py           | 10 ++++++++--
 masque/test/test_library.py | 20 ++++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/masque/library.py b/masque/library.py
index db9dda5..88799ec 100644
--- a/masque/library.py
+++ b/masque/library.py
@@ -22,7 +22,7 @@ import copy
 from pprint import pformat
 from collections import defaultdict
 from abc import ABCMeta, abstractmethod
-from graphlib import TopologicalSorter
+from graphlib import TopologicalSorter, CycleError
 
 import numpy
 from numpy.typing import ArrayLike, NDArray
@@ -618,7 +618,13 @@ class ILibraryView(Mapping[str, 'Pattern'], metaclass=ABCMeta):
         Return:
             Topologically sorted list of pattern names.
         """
-        return cast('list[str]', list(TopologicalSorter(self.child_graph(dangling=dangling)).static_order()))
+        try:
+            return cast('list[str]', list(TopologicalSorter(self.child_graph(dangling=dangling)).static_order()))
+        except CycleError as exc:
+            cycle = exc.args[1] if len(exc.args) > 1 else None
+            if cycle is None:
+                raise LibraryError('Cycle found while building child order') from exc
+            raise LibraryError(f'Cycle found while building child order: {cycle}') from exc
 
     def find_refs_local(
             self,
diff --git a/masque/test/test_library.py b/masque/test/test_library.py
index 56ee3d7..e66b7cc 100644
--- a/masque/test/test_library.py
+++ b/masque/test/test_library.py
@@ -293,6 +293,26 @@ def test_library_subtree() -> None:
     assert "c" not in sub
 
 
+def test_library_child_order_cycle_raises_library_error() -> None:
+    lib = Library()
+    lib["a"] = Pattern()
+    lib["a"].ref("b")
+    lib["b"] = Pattern()
+    lib["b"].ref("a")
+
+    with pytest.raises(LibraryError, match="Cycle found while building child order"):
+        lib.child_order()
+
+
+def test_library_find_refs_global_cycle_raises_library_error() -> None:
+    lib = Library()
+    lib["a"] = Pattern()
+    lib["a"].ref("a")
+
+    with pytest.raises(LibraryError, match="Cycle found while building child order"):
+        lib.find_refs_global("a")
+
+
 def test_library_get_name() -> None:
     lib = Library()
     lib["cell"] = Pattern()