Add Lhotse issue workaround

Signed-off-by: Piotr Żelasko <[email protected]>

nemo/collections/asr/data/audio_to_text_lhotse_prompted.py

@@ -16,6 +16,7 @@
 
 import torch.utils.data
 from lhotse import CutSet
+from lhotse.cut import MixedCut
 from lhotse.dataset import AudioSamples
 from lhotse.dataset.collation import collate_vectors
 
@@ -99,7 +100,7 @@ def __getitem__(self, cuts: CutSet) -> PromptedAudioToTextMiniBatch:
             prompt_lens=prompt_lens,
             prompted_transcript=prompts_with_answers,
             prompted_transcript_lens=prompts_with_answers_lens,
-            cuts=cuts.drop_in_memory_data(),
+            cuts=_drop_in_memory_data(cuts),
         )
 
     def _collate_tokens(self, tokens: list[Union[list[int], torch.Tensor]]) -> tuple[torch.Tensor, torch.Tensor]:
@@ -111,3 +112,24 @@ def _collate_tokens(self, tokens: list[Union[list[int], torch.Tensor]]) -> tuple
 
 class ProbablyIncorrectLanguageKeyError(RuntimeError):
     pass
+
+
+def _drop_in_memory_data(
+    cuts: CutSet,
+    _fields=frozenset(MixedCut.__dataclass_fields__.keys()),
+) -> CutSet:
+    """Workaround for an edge case in cuts.drop_in_memory_data() on MixedCut with Lhotse<1.29.0"""
+    ans = []
+    for c in cuts:
+        # Not a mixed cut or a mixed cut that wasn't assigned any extra attributes.
+        if not isinstance(c, MixedCut) or _fields.issuperset(c.__dict__.keys()):
+            ans.append(c.drop_in_memory_data())
+        else:
+            extra_attrs = {k: v for k, v in c.__dict__.items() if k not in _fields}
+            for k in extra_attrs:
+                delattr(c, k)
+            ans.append(c.drop_in_memory_data())
+            for k, v in extra_attrs.items():
+                setattr(ans[-1], k, v)
+                setattr(c, k, v)
+    return CutSet(ans)