added a warning whenever added fields use different meshes

Author: Wyatt Sieminski

src/parcels/_core/fieldset.py

@@ -2,6 +2,7 @@
 
 import functools
 import sys
+import warnings
 from collections.abc import Iterable
 from typing import IO, TYPE_CHECKING
 
@@ -21,6 +22,7 @@
 from parcels._core.utils.string import _assert_str_and_python_varname
 from parcels._core.utils.time import get_datetime_type_calendar
 from parcels._core.utils.time import is_compatible as datetime_is_compatible
+from parcels._core.warnings import FieldSetWarning
 from parcels._python import NOTSET, NotSetType
 from parcels._reprs import fieldset_describe
 from parcels.interpolators import (
@@ -73,6 +75,7 @@ def __init__(self, models: list[ModelData]):
         self._fields: dict[str, Field | VectorField] | None = None
         self.reconstruct_fields()
         self.context: dict[str, float] = {}
+        _warn_if_fields_use_different_meshes(self.fields.values())
 
     def __setattr__(self, name, value):
         """Set field attribute by name. If context exists and name in context, raise error to prevent overwriting context variable."""
@@ -151,6 +154,7 @@ def add_field(self, field: Field, name: str | None = None):
             raise ValueError(f"FieldSet already has a Field with name '{name}'")
 
         self.fields[name] = field
+        _warn_if_fields_use_different_meshes(self.fields.values())
 
     def to_windowed_arrays(self, *, max_levels: int | None = None):
         """Wrap dask-backed field data in rolling time-window caches.
@@ -215,6 +219,7 @@ def add_constant_field(self, name: str, value, mesh: ptyping.Mesh = "spherical")
         self.reconstruct_fields()
         field = getattr(self, name)
         field.interp_method = XConstantField()
+        _warn_if_fields_use_different_meshes(self.fields.values())
 
     def add_context(self, name, value):
         """Add context variable to the FieldSet.
@@ -362,6 +367,28 @@ def assert_compatible_fieldsets(left: FieldSet, right: FieldSet) -> None:
         )
 
 
+def _warn_if_fields_use_different_meshes(fields: Iterable[Field | VectorField]):
+    """Warn if multiple fields use different meshes on the underlying grids.
+
+    Parameters
+    ----------
+    fields : Iterable[Field | VectorField]
+        The fields to check for conflicting meshes.
+
+    Warns
+    ------
+    FieldSetWarning
+        If the fields have different meshes on the underlying grids.
+    """
+    meshes = {field.grid._mesh for field in fields}
+    if len(meshes) > 1:
+        warnings.warn(
+            f"FieldSet has multiple different meshes: {meshes}. This may lead to unexpected behavior during execution.",
+            category=FieldSetWarning,
+            stacklevel=2,
+        )
+
+
 class CalendarError(Exception):  # TODO: Move to a parcels errors module
     """Exception raised when the calendar of a field is not compatible with the rest of the Fields. The user should ensure that they only add fields to a FieldSet that have compatible CFtime calendars."""