Pint support for top-level functions

ci/azure/install.yml

@@ -27,6 +27,7 @@ steps:
         git+https://github.com/zarr-developers/zarr \
         git+https://github.com/Unidata/cftime \
         git+https://github.com/mapbox/rasterio \
+        git+https://github.com/hgrecco/pint \
         git+https://github.com/pydata/bottleneck
   condition: eq(variables['UPSTREAM_DEV'], 'true')
   displayName: Install upstream dev dependencies

xarray/core/variable.py

@@ -739,7 +739,11 @@ def _getitem_with_mask(self, key, fill_value=dtypes.NA):
 
             data = as_indexable(self._data)[actual_indexer]
             mask = indexing.create_mask(indexer, self.shape, data)
-            data = duck_array_ops.where(mask, fill_value, data)
+            if isinstance(mask, bool):
+                mask = not mask
+            else:
+                mask = ~mask
+            data = duck_array_ops.where(mask, data, fill_value)
         else:
             # array cannot be indexed along dimensions of size 0, so just
             # build the mask directly instead.