From 20f37ea0f78e79be142c2de8db7d63cdfab5e8d0 Mon Sep 17 00:00:00 2001
From: Jan Petykiewicz <jan@mpxd.net>
Date: Wed, 1 Apr 2026 21:58:56 -0700
Subject: [PATCH] [ell] validate spacing length

---
 masque/builder/utils.py     | 11 ++++++++++-
 masque/test/test_builder.py | 18 ++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/masque/builder/utils.py b/masque/builder/utils.py
index b64cb85..4de6dbb 100644
--- a/masque/builder/utils.py
+++ b/masque/builder/utils.py
@@ -132,8 +132,17 @@ def ell(
     if spacing is None:
         ch_offsets = numpy.zeros_like(y_order)
     else:
+        spacing_arr = numpy.asarray(spacing, dtype=float).reshape(-1)
         steps = numpy.zeros_like(y_order)
-        steps[1:] = spacing
+        if spacing_arr.size == 1:
+            steps[1:] = spacing_arr[0]
+        elif spacing_arr.size == len(ports) - 1:
+            steps[1:] = spacing_arr
+        else:
+            raise BuildError(
+                f'spacing must be scalar or have length {len(ports) - 1} for {len(ports)} ports; '
+                f'got length {spacing_arr.size}'
+                )
         ch_offsets = numpy.cumsum(steps)[y_ind]
 
     x_start = rot_offsets[:, 0]
diff --git a/masque/test/test_builder.py b/masque/test/test_builder.py
index 0553b75..309dab6 100644
--- a/masque/test/test_builder.py
+++ b/masque/test/test_builder.py
@@ -1,7 +1,11 @@
+import numpy
+import pytest
 from numpy.testing import assert_equal, assert_allclose
 from numpy import pi
 
 from ..builder import Builder
+from ..builder.utils import ell
+from ..error import BuildError
 from ..library import Library
 from ..pattern import Pattern
 from ..ports import Port
@@ -131,6 +135,20 @@ def test_dead_plug_best_effort() -> None:
     assert_allclose(b.ports['B'].rotation, 0, atol=1e-10)
 
 
+def test_ell_validates_spacing_length() -> None:
+    ports = {
+        'A': Port((0, 0), 0),
+        'B': Port((0, 1), 0),
+        'C': Port((0, 2), 0),
+    }
+
+    with pytest.raises(BuildError, match='spacing must be scalar or have length 2'):
+        ell(ports, True, 'min_extension', 5, spacing=[1, 2, 3])
+
+    with pytest.raises(BuildError, match='spacing must be scalar or have length 2'):
+        ell(ports, True, 'min_extension', 5, spacing=[])
+
+
 def test_ell_handles_array_spacing_when_ccw_none() -> None:
     ports = {
         'A': Port((0, 0), 0),