Fix rolling mean on bool arrays (pydata#10319)

* set count's dtype to int

* add test for the MR, and fix failing test

* remove comments

---------

Co-authored-by: Giacomo Caria <giacomo@chloris.earth>

Author: gcaria

xarray/computation/rolling.py

@@ -196,10 +196,13 @@ def method(self, keep_attrs=None, **kwargs):
 
     def _mean(self, keep_attrs, **kwargs):
         result = self.sum(keep_attrs=False, **kwargs) / duck_array_ops.astype(
-            self.count(keep_attrs=False), dtype=self.obj.dtype, copy=False
+            self.count(keep_attrs=False), dtype=int, copy=False
         )
         if keep_attrs:
             result.attrs = self.obj.attrs
+
+        if self.obj.dtype.kind not in "bi":
+            result = result.astype(self.obj.dtype, copy=False)
         return result
 
     _mean.__doc__ = _ROLLING_REDUCE_DOCSTRING_TEMPLATE.format(name="mean")

xarray/tests/test_rolling.py

@@ -433,6 +433,20 @@ def test_rolling_dask_dtype(self, dtype) -> None:
         chunked_result = data.chunk({"x": 1}).rolling(x=3, min_periods=1).mean()
         assert chunked_result.dtype == unchunked_result.dtype
 
+    def test_rolling_mean_bool(self) -> None:
+        bool_raster = DataArray(
+            data=[0, 1, 1, 0, 1, 0],
+            dims=("x"),
+        ).astype(bool)
+
+        expected = DataArray(
+            data=[np.nan, 2 / 3, 2 / 3, 2 / 3, 1 / 3, np.nan],
+            dims=("x"),
+        )
+
+        result = bool_raster.rolling(x=3, center=True).mean()
+        assert_allclose(result, expected)
+
 
 @requires_numbagg
 class TestDataArrayRollingExp: