Propagate attributes for index variables.

Author: dcherian

xarray/core/parallel.py

@@ -541,6 +541,9 @@ def map_blocks(
         hlg.layers[gname_l] = layer
 
     result = Dataset(coords=indexes, attrs=template.attrs)
+    for index in result.indexes:
+        result[index].attrs = template[index].attrs
+
     for name, gname_l in var_key_map.items():
         dims = template[name].dims
         var_chunks = []

xarray/tests/test_dask.py

@@ -972,6 +972,7 @@ def make_da():
         coords={"x": np.arange(10), "y": np.arange(100, 120)},
         name="a",
     ).chunk({"x": 4, "y": 5})
+    da.x.attrs["long_name"] = "x"
     da.attrs["test"] = "test"
     da.coords["c2"] = 0.5
     da.coords["ndcoord"] = da.x * 2
@@ -995,6 +996,9 @@ def make_ds():
     map_ds.attrs["test"] = "test"
     map_ds.coords["xx"] = map_ds["a"] * map_ds.y
 
+    map_ds.x.attrs["long_name"] = "x"
+    map_ds.y.attrs["long_name"] = "y"
+
     return map_ds