Handle when no reclustered jets are available for MC

If not otherwise handled, it will raise an exception that will bubble up
to the steering, appearing as a failure. This isn't wrong (we can't
recluster if there are no jets...), but it's a bit surprising to see failed
tasks. Better to handle it explicitly and pass on the message, as is
done for other cases (ie. for the one level and three level)

src/mammoth/reclustered_substructure/analyze_chunk.py

@@ -383,24 +383,36 @@ def analyze_track_skim_and_recluster_MC(
     )
 
     # Reclustering
-    logger.info("Reclustering jets...")
-    for level in ["part_level", "det_level"]:
-        # We only do the area calculation for data.
-        reclustering_kwargs = {**reclustering_settings}
-        if level != "part_level":
-            reclustering_kwargs["area_settings"] = jet_finding.AreaSubstructure(**area_kwargs)
-        # Add in the generator specific customizations
-        if gen_settings and jet_finding_settings_additional_kwargs[level]:
-            reclustering_settings.update(jet_finding_settings_additional_kwargs[level])
-        logger.info(f"Reclustering {level} jets with {reclustering_kwargs}...")
-        jets[level, "reclustering"] = jet_finding.recluster_jets(
-            jets=jets[level],
-            jet_finding_settings=jet_finding.ReclusteringJetFindingSettings(
-                **reclustering_kwargs,
-            ),
-            store_recursive_splittings=True,
-        )
-    logger.info("Done with reclustering")
+    # If we're out of jets, reclustering will fail. So if we're out of jets, then skip this step
+    # NOTE: We need to select a level to use for checking jets. We select the part_level arbitrarily
+    #       (it shouldn't matter overly much because we've required jet matching at this point)
+    # NOTE: We need to flatten since we could just have empty events.
+    # NOTE: Further, we need to access some variable to avoid flattening into a record, so we select px arbitrarily.
+    # NOTE: We have to use pt because of awkward #2207 (https://github.com/scikit-hep/awkward/issues/2207)
+    _there_are_jets_left = len(ak.flatten(jets["part_level"].pt, axis=None)) > 0
+    # Now, we actually run the reclustering if possible
+    if not _there_are_jets_left:
+        logger.warning("No jets left for reclustering. Skipping reclustering...")
+    else:
+        logger.info("Reclustering jets...")
+        for level in ["part_level", "det_level"]:
+            # We only do the area calculation for data.
+            reclustering_kwargs = {**reclustering_settings}
+            if level != "part_level":
+                reclustering_kwargs["area_settings"] = jet_finding.AreaSubstructure(**area_kwargs)
+            # Add in the generator specific customizations
+            if gen_settings and jet_finding_settings_additional_kwargs[level]:
+                reclustering_settings.update(jet_finding_settings_additional_kwargs[level])
+            logger.info(f"Reclustering {level} jets with {reclustering_kwargs}...")
+            jets[level, "reclustering"] = jet_finding.recluster_jets(
+                jets=jets[level],
+                jet_finding_settings=jet_finding.ReclusteringJetFindingSettings(
+                    **reclustering_kwargs,
+                ),
+                store_recursive_splittings=True,
+            )
+
+        logger.info("Done with reclustering")
 
     logger.info(f"n events: {len(jets)}")
     logger.info(f"n jets accepted: {np.count_nonzero(np.asarray(ak.flatten(jets['det_level'].px, axis=None)))}")