From c32168dc64d50cca87b7b44fbd888c4167fc7f4b Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Mon, 30 Mar 2026 21:17:33 -0700
Subject: [PATCH] [ILibraryView / Pattern] flatten() should raise PatternError
 if asked to preserve ports from a repeated ref

---
 masque/library.py           |  5 +++++
 masque/pattern.py           |  5 +++++
 masque/test/test_library.py | 14 ++++++++++++++
 masque/test/test_pattern.py | 12 ++++++++++++
 4 files changed, 36 insertions(+)

diff --git a/masque/library.py b/masque/library.py
index 5b32260..afd25c6 100644
--- a/masque/library.py
+++ b/masque/library.py
@@ -308,6 +308,11 @@ class ILibraryView(Mapping[str, 'Pattern'], metaclass=ABCMeta):
                     continue
 
                 for ref in pat.refs[target]:
+                    if flatten_ports and ref.repetition is not None and target_pat.ports:
+                        raise PatternError(
+                            f'Cannot flatten ports from repeated ref to {target!r}; '
+                            'flatten with flatten_ports=False or expand/rename the ports manually first.'
+                            )
                     p = ref.as_pattern(pattern=target_pat)
                     if not flatten_ports:
                         p.ports.clear()
diff --git a/masque/pattern.py b/masque/pattern.py
index 9014298..0a66aee 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -1082,6 +1082,11 @@ class Pattern(PortList, AnnotatableImpl, Mirrorable):
                     continue
 
                 for ref in refs:
+                    if flatten_ports and ref.repetition is not None and target_pat.ports:
+                        raise PatternError(
+                            f'Cannot flatten ports from repeated ref to {target!r}; '
+                            'flatten with flatten_ports=False or expand/rename the ports manually first.'
+                            )
                     p = ref.as_pattern(pattern=target_pat)
                     if not flatten_ports:
                         p.ports.clear()
diff --git a/masque/test/test_library.py b/masque/test/test_library.py
index 5b143fa..9eb705e 100644
--- a/masque/test/test_library.py
+++ b/masque/test/test_library.py
@@ -77,6 +77,20 @@ def test_library_flatten_preserves_ports_only_child() -> None:
     assert tuple(flat_parent.ports["P1"].offset) == (11.0, 12.0)
 
 
+def test_library_flatten_repeated_ref_with_ports_raises() -> None:
+    lib = Library()
+    child = Pattern(ports={"P1": Port((1, 2), 0)})
+    child.polygon((1, 0), vertices=[[0, 0], [1, 0], [0, 1]])
+    lib["child"] = child
+
+    parent = Pattern()
+    parent.ref("child", repetition=Grid(a_vector=(10, 0), a_count=2))
+    lib["parent"] = parent
+
+    with pytest.raises(PatternError, match='Cannot flatten ports from repeated ref'):
+        lib.flatten("parent", flatten_ports=True)
+
+
 def test_lazy_library() -> None:
     lib = LazyLibrary()
     called = 0
diff --git a/masque/test/test_pattern.py b/masque/test/test_pattern.py
index 338bd39..b459502 100644
--- a/masque/test/test_pattern.py
+++ b/masque/test/test_pattern.py
@@ -114,6 +114,18 @@ def test_pattern_flatten_preserves_ports_only_child() -> None:
     assert parent.ports["P1"].rotation == 0
     assert tuple(parent.ports["P1"].offset) == (11.0, 12.0)
 
+
+def test_pattern_flatten_repeated_ref_with_ports_raises() -> None:
+    child = Pattern(ports={"P1": Port((1, 2), 0)})
+    child.polygon((1, 0), vertices=[[0, 0], [1, 0], [0, 1]])
+
+    parent = Pattern()
+    parent.ref("child", repetition=Grid(a_vector=(10, 0), a_count=2))
+
+    with pytest.raises(PatternError, match='Cannot flatten ports from repeated ref'):
+        parent.flatten({"child": child}, flatten_ports=True)
+
+
 def test_pattern_interface() -> None:
     source = Pattern()
     source.ports["A"] = Port((10, 20), 0, ptype="test")