Fix .chunks loading lazy backed array data (#6721)

Author: dcherian

doc/whats-new.rst

@@ -212,6 +212,8 @@ Bug fixes
 - Fixed silent overflow issue when decoding times encoded with 32-bit and below
   unsigned integer data types (:issue:`6589`, :pull:`6598`).
   By `Spencer Clark <https://github.com/spencerkclark>`_.
+- Fixed ``.chunks`` loading lazy data (:issue:`6538`).
+  By `Deepak Cherian <https://github.com/dcherian>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/core/common.py

@@ -1718,7 +1718,7 @@ def get_chunksizes(
 
     chunks: dict[Any, tuple[int, ...]] = {}
     for v in variables:
-        if hasattr(v.data, "chunks"):
+        if hasattr(v._data, "chunks"):
             for dim, c in v.chunksizes.items():
                 if dim in chunks and c != chunks[dim]:
                     raise ValueError(

xarray/tests/test_dataset.py

@@ -992,6 +992,13 @@ def test_attrs(self) -> None:
         assert data.attrs["foobar"], "baz"
         assert isinstance(data.attrs, dict)
 
+    def test_chunks_does_not_load_data(self) -> None:
+        # regression test for GH6538
+        store = InaccessibleVariableDataStore()
+        create_test_data().dump_to_store(store)
+        ds = open_dataset(store)
+        assert ds.chunks == {}
+
     @requires_dask
     def test_chunk(self) -> None:
         data = create_test_data()