Cast to >=float32 tensor when passing scalar to self.log (#19046)

Co-authored-by: awaelchli <[email protected]>
(cherry picked from commit 1fcb4ae)

src/lightning/pytorch/CHANGELOG.md

@@ -47,6 +47,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed an issue parsing the version from folders that don't include a version number in `TensorBoardLogger` and `CSVLogger` ([#18897](https://github.com/Lightning-AI/lightning/issues/18897))
 
 
+- Fixed the tensor conversion in `self.log` to respect the default dtype ([#19046](https://github.com/Lightning-AI/lightning/issues/19046))
+
+
 ## [2.1.0] - 2023-10-11
 
 ### Added

src/lightning/pytorch/core/module.py

@@ -61,6 +61,7 @@
 from lightning.pytorch.loggers import Logger
 from lightning.pytorch.trainer import call
 from lightning.pytorch.trainer.connectors.logger_connector.fx_validator import _FxValidator
+from lightning.pytorch.trainer.connectors.logger_connector.result import _get_default_dtype
 from lightning.pytorch.utilities import GradClipAlgorithmType
 from lightning.pytorch.utilities.exceptions import MisconfigurationException
 from lightning.pytorch.utilities.imports import _TORCHMETRICS_GREATER_EQUAL_0_9_1
@@ -626,7 +627,11 @@ def __check_allowed(v: Any, name: str, value: Any) -> None:
         raise ValueError(f"`self.log({name}, {value})` was called, but `{type(v).__name__}` values cannot be logged")
 
     def __to_tensor(self, value: Union[Tensor, numbers.Number], name: str) -> Tensor:
-        value = value.clone().detach() if isinstance(value, Tensor) else torch.tensor(value, device=self.device)
+        value = (
+            value.clone().detach()
+            if isinstance(value, Tensor)
+            else torch.tensor(value, device=self.device, dtype=_get_default_dtype())
+        )
         if not torch.numel(value) == 1:
             raise ValueError(
                 f"`self.log({name}, {value})` was called, but the tensor must have a single element."