From 2ddf9e82b49c790596e12e58973463c038c73e1c Mon Sep 17 00:00:00 2001
From: tchaton <thomas@grid.ai>
Date: Mon, 16 Aug 2021 11:44:27 +0200
Subject: [PATCH 1/2] resolve bug

---
 .../connectors/logger_connector/result.py     | 14 +++++-----
 .../logging_/test_eval_loop_logging.py        | 26 +++++++++++++++++++
 2 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/pytorch_lightning/trainer/connectors/logger_connector/result.py b/pytorch_lightning/trainer/connectors/logger_connector/result.py
index 2b2e4613f2298..3db7c25f5e560 100644
--- a/pytorch_lightning/trainer/connectors/logger_connector/result.py
+++ b/pytorch_lightning/trainer/connectors/logger_connector/result.py
@@ -289,9 +289,12 @@ class ResultMetricCollection(dict):
     with the same metadata.
     """
 
-    def __init__(self, *args, metadata: Optional[_Metadata] = None) -> None:
+    def __init__(self, *args) -> None:
         super().__init__(*args)
-        self.meta = metadata
+
+    @property
+    def meta(self) -> _Metadata:
+        return list(self.values())[0].meta
 
     def __getstate__(self, drop_value: bool = False) -> dict:
         def getstate(item: ResultMetric) -> dict:
@@ -313,9 +316,6 @@ def setstate(item: dict) -> Union[Dict[str, ResultMetric], ResultMetric, Any]:
         items = setstate(state["items"])
         self.update(items)
 
-        any_result_metric = next(iter(items.values()))
-        self.meta = any_result_metric.meta
-
     @classmethod
     def _reconstruct(cls, state: dict, sync_fn: Optional[Callable] = None) -> "ResultMetricCollection":
         rmc = cls()
@@ -480,7 +480,7 @@ def fn(v: _METRIC) -> ResultMetric:
 
         value = apply_to_collection(value, (torch.Tensor, Metric), fn)
         if isinstance(value, dict):
-            value = ResultMetricCollection(value, metadata=meta)
+            value = ResultMetricCollection(value)
         self[key] = value
 
     def update_metrics(self, key: str, value: _METRIC_COLLECTION) -> None:
@@ -591,7 +591,7 @@ def extract_batch_size(self, batch: Any) -> None:
 
     def to(self, *args, **kwargs) -> "ResultCollection":
         """Move all data to the given device."""
-
+        # the meta reference is lost there for ``ResultMetricCollection``.
         self.update(apply_to_collection(dict(self), (torch.Tensor, Metric), move_data_to_device, *args, **kwargs))
 
         if self.minimize is not None:
diff --git a/tests/trainer/logging_/test_eval_loop_logging.py b/tests/trainer/logging_/test_eval_loop_logging.py
index b46641849c6b6..8579bc044734a 100644
--- a/tests/trainer/logging_/test_eval_loop_logging.py
+++ b/tests/trainer/logging_/test_eval_loop_logging.py
@@ -590,3 +590,29 @@ def get_metrics_at_idx(idx):
         "test_loss",
     }
     assert set(results[0]) == {"test_loss"}
+
+
+def test_logging_dict_on_validation_step(tmpdir):
+    class TestModel(BoringModel):
+        def validation_step(self, batch, batch_idx):
+            loss = super().validation_step(batch, batch_idx)
+            loss = loss["x"]
+            metrics = {
+                "loss": loss,
+                "loss_1": loss,
+            }
+            self.log("val_metrics", metrics)
+
+        validation_epoch_end = None
+
+    model = TestModel()
+
+    trainer = Trainer(
+        default_root_dir=tmpdir,
+        limit_train_batches=2,
+        limit_val_batches=2,
+        max_epochs=2,
+        progress_bar_refresh_rate=1,
+    )
+
+    trainer.fit(model)

From 833083c896fb11c56fc7fd5ff0f6643e19d91c54 Mon Sep 17 00:00:00 2001
From: tchaton <thomas@grid.ai>
Date: Mon, 16 Aug 2021 11:46:56 +0200
Subject: [PATCH 2/2] update changelog

---
 CHANGELOG.md                                                  | 4 ++++
 .../trainer/connectors/logger_connector/result.py             | 1 -
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b51f0c2e67002..1053894d4dd9e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -176,6 +176,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed infinite loop with CycleIterator and multiple loaders ([#8889](https://github.com/PyTorchLightning/pytorch-lightning/pull/8889))
 
 
+- Fixed lost reference to `_Metadata` object in `ResultMetricCollection` ([#8932](https://github.com/PyTorchLightning/pytorch-lightning/pull/8932))
+
+
+
 ## [1.4.0] - 2021-07-27
 
 ### Added
diff --git a/pytorch_lightning/trainer/connectors/logger_connector/result.py b/pytorch_lightning/trainer/connectors/logger_connector/result.py
index 3db7c25f5e560..77079e6397f6f 100644
--- a/pytorch_lightning/trainer/connectors/logger_connector/result.py
+++ b/pytorch_lightning/trainer/connectors/logger_connector/result.py
@@ -591,7 +591,6 @@ def extract_batch_size(self, batch: Any) -> None:
 
     def to(self, *args, **kwargs) -> "ResultCollection":
         """Move all data to the given device."""
-        # the meta reference is lost there for ``ResultMetricCollection``.
         self.update(apply_to_collection(dict(self), (torch.Tensor, Metric), move_data_to_device, *args, **kwargs))
 
         if self.minimize is not None: