BUG: Fix empty Group nodes lacking a "consolidated_metadata" field#3967
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TomAugspurger merged 3 commits intoMay 12, 2026
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All nodes opened via `open_consolidated` are expected to have a non-null `.metadata.consolidated_metadata`. zarr-developers#3954 showed an example, with a data file written by zarr-python 2.x, where that condition failed to hold. This happened because of a slight difference between how zarr-python 3.x writes consolidated metadata and how zarr-python 2.x wrote it. For leaf `Group` nodes (a `Group` with no `Group` or `Array` children), zarr-python 3.x includes an "empty" `consolidated_metadata` field. In zarr-python 3.x, we include a `consolidated_metadata: metadata: {}` field to indicate that it's empty. zarr-python 2.x *didn't* include that. The fix is to update how we load this type of data. We effectively normalize a node missing consolidated metadata to one that is known not to have consolidated metadata (which is consistent with the idea behind consolidated metadata: just do one metadata read up front).
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| if isinstance(child, GroupMetadata) and child.consolidated_metadata is None: | ||
| child = replace(child, consolidated_metadata=ConsolidatedMetadata(metadata={})) |
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This is the new bit. The rest is rewriting the dict comprehension to a for loop.
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #3967 +/- ##
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Coverage 93.27% 93.28%
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Files 87 87
Lines 11739 11745 +6
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+ Hits 10950 10956 +6
Misses 789 789
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All nodes opened via
open_consolidatedare expected to have a non-null.metadata.consolidated_metadata. #3954 showed an example, with a data file written by zarr-python 2.x, where that condition failed to hold.This happened because of a slight difference between how zarr-python 3.x writes consolidated metadata and how zarr-python 2.x wrote it. For leaf
Groupnodes (aGroupwith noGrouporArraychildren), zarr-python 3.x includes an "empty"consolidated_metadatafield. In zarr-python 3.x, we include aconsolidated_metadata: metadata: {}field to indicate that it's empty. zarr-python 2.x didn't include that.The fix is to update how we load this type of data. We effectively normalize a node missing consolidated metadata to one that is known not to have consolidated metadata (which is consistent with the idea behind consolidated metadata: just do one metadata read up front).
Closes #3954
TODO:
docs/user-guide/*.mdchanges/