fix validation of CustomGridBoundaries

Author: dmarek-flex

CHANGELOG.md

@@ -30,6 +30,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - If `ModeSpec.angle_rotation=True` for a mode object, validate that the structure rotation can be successfully done. Also, error if the medium cannot be rotated (e.g. anisotropic or custom medium), which would previously have just produced wrong results.
 - Characteristic impedance calculations in the `ImpedanceCalculator` using definitions that rely on flux, which were giving incorrect results for lossy transmission lines.
 - Fixed handling of symmetry when creating adjoint field sources and added warning when broken up adjoint simulations do not have the same symmetry as the forward simulation.
+- Validation for `CustomGridBoundaries`, which was previously allowing unsorted arrays and arrays with less than two entries.
 
 ### Changed
 - Relaxed bounds checking of path integrals during `WavePort` validation.

tests/test_components/test_grid_spec.py

@@ -544,3 +544,13 @@ def test_uniform_grid_dl_validation(dl, expect_exception):
             grid_spec=td.GridSpec.uniform(dl=dl),
             run_time=1e-12,
         )
+
+
+def test_custom_grid_boundary_validation():
+    """Tests that the 'coords' is at least length 2 and sorted in ascending order."""
+
+    with pytest.raises(pydantic.ValidationError):
+        _ = td.CustomGridBoundaries(coords=[10])
+
+    with pytest.raises(pydantic.ValidationError):
+        _ = td.CustomGridBoundaries(coords=[9, 10, 9, 10, 11, 9, 8])

tidy3d/components/grid/grid_spec.py

@@ -419,6 +419,23 @@ def estimated_min_dl(
 
         return min(np.diff(self.coords))
 
+    @pd.validator("coords", always=True)
+    def _validate_coords(cls, val):
+        """
+        Ensure 'coords' is sorted and has at least 2 entries.
+        """
+        if len(val) < 2:
+            raise SetupError("You must supply at least 2 entries for 'coords'.")
+        # Ensure coords is sorted
+        positive_diff = np.diff(val) > 0
+        if not np.all(positive_diff):
+            violations = np.where(np.diff(val) <= 0)[0] + 1
+            raise SetupError(
+                "'coords' must be strictly increasing (sorted in ascending order). "
+                f"The entries at the following indices violated this requirement: {violations}."
+            )
+        return val
+
 
 class CustomGrid(GridSpec1d):
     """Custom 1D grid supplied as a list of grid cell sizes centered on the simulation center.