Fix: handle missing library_link attribute on Footprint objects in KiCad 9 (#157)

KiCad 9's IPC API returns Footprint objects where fp.definition lacks
the library_link attribute, causing all component queries to fail with
"'Footprint' object has no attribute 'library_link'" warnings and
returning 0 components. This adds a hasattr check with fallback to
fp.definition.id.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_ipc_footprint_library_link_guard.py

@@ -0,0 +1,81 @@
+"""Regression test for IPCBoardAPI.list_components — footprint field guard.
+
+KiCad 9 IPC sometimes returns Footprint objects whose ``definition`` lacks the
+``library_link`` attribute, which used to raise ``AttributeError`` and drop
+every component from ``list_components``. The fix guards the access and falls
+back to ``definition.id`` when present, or an empty string.
+"""
+
+import sys
+from pathlib import Path
+from types import SimpleNamespace
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "python"))
+
+
+# Stub kipy.util.units.to_mm so the module-level import inside list_components
+# succeeds without a real kipy installation.
+_kipy = sys.modules.setdefault("kipy", MagicMock(name="kipy"))
+_kipy_util = sys.modules.setdefault("kipy.util", MagicMock(name="kipy.util"))
+_kipy_units = sys.modules.setdefault("kipy.util.units", MagicMock(name="kipy.util.units"))
+_kipy_units.to_mm = lambda v: v / 1_000_000
+
+
+def _make_fp(*, library_link=None, fp_id=None):
+    """Build a minimal mock Footprint with the requested definition shape."""
+    if library_link is not None and fp_id is not None:
+        definition = SimpleNamespace(library_link=library_link, id=fp_id)
+    elif library_link is not None:
+        definition = SimpleNamespace(library_link=library_link)
+    elif fp_id is not None:
+        definition = SimpleNamespace(id=fp_id)
+    else:
+        definition = SimpleNamespace()  # neither attribute
+
+    fp = SimpleNamespace(
+        position=SimpleNamespace(x=1_000_000, y=2_000_000),
+        reference_field=SimpleNamespace(text=SimpleNamespace(value="R1")),
+        value_field=SimpleNamespace(text=SimpleNamespace(value="220")),
+        definition=definition,
+        orientation=SimpleNamespace(degrees=0),
+        layer="F.Cu",
+        id="fp-uuid-1",
+    )
+    return fp
+
+
+def _list_components_with(fps):
+    """Run IPCBoardAPI.list_components against a list of mock footprints."""
+    from kicad_api.ipc_backend import IPCBoardAPI
+
+    api = IPCBoardAPI.__new__(IPCBoardAPI)
+    fake_board = MagicMock()
+    fake_board.get_footprints.return_value = fps
+    with patch.object(api, "_get_board", return_value=fake_board, create=True):
+        return api.list_components()
+
+
+def test_definition_with_library_link_returned_as_footprint():
+    fp = _make_fp(library_link="Library:Footprint")
+    [comp] = _list_components_with([fp])
+    assert comp["footprint"] == "Library:Footprint"
+
+
+def test_definition_without_library_link_falls_back_to_id():
+    """Regression: the bug we are guarding against."""
+    fp = _make_fp(fp_id="some-fp-id")
+    [comp] = _list_components_with([fp])
+    # Old code raised AttributeError and dropped the component entirely.
+    assert comp["footprint"] == "some-fp-id"
+    assert comp["reference"] == "R1"
+
+
+def test_definition_without_either_attribute_returns_empty_string():
+    fp = _make_fp()
+    [comp] = _list_components_with([fp])
+    assert comp["footprint"] == ""
+    # And the component is still emitted (not silently dropped)
+    assert comp["reference"] == "R1"