Call setup(…) with stage ‘validation’ when running Trainer.validate(…)

pytorch_lightning/core/datamodule.py

@@ -155,6 +155,7 @@ def __init__(
         # Private attrs to keep track of whether or not data hooks have been called yet
         self._has_prepared_data = False
         self._has_setup_fit = False
+        self._has_setup_validation = False
         self._has_setup_test = False
 
     @property
@@ -230,6 +231,15 @@ def has_setup_fit(self):
         """
         return self._has_setup_fit
 
+    @property
+    def has_setup_validation(self):
+        """Return bool letting you know if datamodule.setup('validation') has been called or not.
+
+        Returns:
+            bool: True if datamodule.setup('validation') has been called. False by default.
+        """
+        return self._has_setup_validation
+
     @property
     def has_setup_test(self):
         """Return bool letting you know if datamodule.setup('test') has been called or not.

pytorch_lightning/trainer/trainer.py

@@ -917,11 +917,18 @@ def tune(
 
     def call_setup_hook(self, model):
         # call setup after the ddp process has connected
-        stage_name = 'test' if self.testing else 'fit'
+        stage_name = self.evaluating or 'fit'
+
         if self.datamodule is not None:
-            called = self.datamodule.has_setup_test if self.testing else self.datamodule.has_setup_fit
+            called = {
+                False: self.datamodule.has_setup_fit,
+                'validation': self.datamodule.has_setup_validation,
+                'test': self.datamodule.has_setup_test,
+            }[self.evaluating]
+
             if not called:
                 self.datamodule.setup(stage_name)
+
         self.setup(model, stage_name)
         model.setup(stage_name)