Validate matching shapes for precomputed corridor surfaces

xrspatial/corridor.py

@@ -25,7 +25,7 @@
 import xarray as xr
 
 from xrspatial.cost_distance import cost_distance
-from xrspatial.utils import _validate_raster
+from xrspatial.utils import _validate_matching_shape, _validate_raster
 
 
 def _scalar_to_float(da_scalar):
@@ -207,6 +207,21 @@ def least_cost_corridor(
     # ------------------------------------------------------------------
     if precomputed:
         cd_surfaces = list(sources)
+        # cost_distance() guarantees matching shapes when it runs, but the
+        # precomputed path bypasses it.  Without this check, surfaces of
+        # differing shape get silently aligned on the intersection of their
+        # coordinates by xarray, producing a truncated, wrong-valued corridor.
+        # Like cost_distance, this guards shape only; mismatched coordinates
+        # on same-shape surfaces are out of scope.
+        expected_shape = cd_surfaces[0].shape
+        for i, cd in enumerate(cd_surfaces[1:], start=1):
+            _validate_matching_shape(
+                cd,
+                expected_shape,
+                func_name="least_cost_corridor",
+                name=f"precomputed surface {i}",
+                expected_name="precomputed surface 0",
+            )
         # No friction surface to draw grid metadata from -- keep the
         # existing source-derived attrs/name behaviour.
         geo_source = None

xrspatial/tests/test_corridor.py

@@ -376,6 +376,43 @@ def test_single_source_in_list_raises():
         least_cost_corridor(friction, sources=[src])
 
 
+def test_precomputed_mismatched_shape_raises():
+    """Precomputed surfaces of differing shape raise instead of aligning.
+
+    Without the shape check, xarray silently aligns the two surfaces on the
+    intersection of their coordinates and returns a truncated corridor with
+    wrong values (e.g. 4x4 + 3x3 -> an all-zero 3x3 result).
+    """
+    friction = _make_raster(np.ones((4, 4)))
+    cd_a = _make_raster(np.ones((4, 4)))
+    cd_b = _make_raster(np.ones((3, 3)))
+    with pytest.raises(ValueError, match="does not match"):
+        least_cost_corridor(friction, cd_a, cd_b, precomputed=True)
+
+
+def test_precomputed_mismatched_shape_pairwise_raises():
+    """Pairwise precomputed surfaces of differing shape raise."""
+    friction = _make_raster(np.ones((4, 4)))
+    sources = [
+        _make_raster(np.ones((4, 4))),
+        _make_raster(np.ones((3, 3))),
+    ]
+    with pytest.raises(ValueError, match="does not match"):
+        least_cost_corridor(
+            friction, sources=sources, precomputed=True, pairwise=True
+        )
+
+
+@pytest.mark.skipif(da is None, reason="dask not installed")
+def test_precomputed_mismatched_shape_dask_raises():
+    """The shape check fires on dask surfaces without triggering a compute."""
+    friction = _make_raster(np.ones((4, 4)), backend="dask+numpy", chunks=(4, 4))
+    cd_a = _make_raster(np.ones((4, 4)), backend="dask+numpy", chunks=(4, 4))
+    cd_b = _make_raster(np.ones((3, 3)), backend="dask+numpy", chunks=(3, 3))
+    with pytest.raises(ValueError, match="does not match"):
+        least_cost_corridor(friction, cd_a, cd_b, precomputed=True)
+
+
 # -----------------------------------------------------------------------
 # Metadata propagation (issue #3446)
 # -----------------------------------------------------------------------