reindex: fix missing variable metadata (#6389)

Author: benbovy

xarray/core/dataset.py

@@ -2545,6 +2545,13 @@ def _reindex_callback(
         new_variables = variables.copy()
         new_indexes = indexes.copy()
 
+        # re-assign variable metadata
+        for name, new_var in new_variables.items():
+            var = self._variables.get(name)
+            if var is not None:
+                new_var.attrs = var.attrs
+                new_var.encoding = var.encoding
+
         # pass through indexes from excluded dimensions
         # no extra check needed for multi-coordinate indexes, potential conflicts
         # should already have been detected when aligning the indexes

xarray/tests/test_dataset.py

@@ -1887,6 +1887,19 @@ def test_reindex(self):
         actual = ds.reindex(x=[0, 1, 3], y=[0, 1])
         assert_identical(expected, actual)
 
+    def test_reindex_attrs_encoding(self):
+        ds = Dataset(
+            {"data": ("x", [1, 2, 3])},
+            {"x": ("x", [0, 1, 2], {"foo": "bar"}, {"bar": "baz"})},
+        )
+        actual = ds.reindex(x=[0, 1])
+        expected = Dataset(
+            {"data": ("x", [1, 2])},
+            {"x": ("x", [0, 1], {"foo": "bar"}, {"bar": "baz"})},
+        )
+        assert_identical(actual, expected)
+        assert actual.x.encoding == expected.x.encoding
+
     def test_reindex_warning(self):
         data = create_test_data()