Adds validator to warn for resample=False for custom XY

Author: DrPaulSharp

cpp/RAT

@@ -361,8 +361,8 @@ def model_post_init(self, __context: Any) -> None:
         """Set up the Class to protect against disallowed modification.
 
         We initialise the class handle in the ClassLists for empty data fields, set protected parameters, get names of
-        all defined parameters, determine the contents of the "model" field in contrasts,
-        and wrap ClassList routines to control revalidation.
+        all defined parameters, determine the contents of the "model" field in contrasts, and wrap ClassList routines
+        to control revalidation.
         """
         # Ensure all ClassLists have the correct _class_handle defined
         for field in (fields := Project.model_fields):
@@ -454,6 +454,19 @@ def set_layers(self) -> "Project":
             self.layers.data = []
         return self
 
+    @model_validator(mode="after")
+    def set_resample(self) -> "Project":
+        """If we are using a custom XY model, warn that the resample setting for each contrast must always be True."""
+        if self.model == LayerModels.CustomXY:
+            for contrast in self.contrasts:
+                if "resample" in contrast.model_fields_set and contrast.resample is False:
+                    warnings.warn(
+                        'For a custom XY calculation, "resample" must be True for each contrast - resetting to True.',
+                        stacklevel=2,
+                    )
+                contrast.resample = True
+        return self
+
     @model_validator(mode="after")
     def set_calculation(self) -> "Project":
         """Apply the calc setting to the project."""