tighten up arg and kwargs handling

rasterio/_io.pyx

@@ -1122,14 +1122,14 @@ cdef class RasterReader(_base.DatasetReader):
         return out
 
 
-    def dataset_mask(self, **kwargs):
+    def dataset_mask(self, *args, window=None, boundless=False):
         """Calculate the dataset's 2D mask. Derived from the individual band masks
         provided by read_masks().
 
         Parameters
         ----------
-        All kwargs except indexes are passed to read_masks()
-        See read_masks for details
+        position args ignored
+        window and boundless are passed directly to read_masks()
         
         Returns
         -------
@@ -1150,7 +1150,10 @@ cdef class RasterReader(_base.DatasetReader):
         in that it applies per-dataset, not per-band
         (see https://trac.osgeo.org/gdal/wiki/rfc15_nodatabitmask)
         """
-        del kwargs['indexes']  # this method determines indexes
+        del args
+        kwargs = {
+            'window': window,
+            'boundless': boundless}
 
         # GDAL found dataset-wide alpha band or mask
         # All band masks are equal so we can return the first

tests/test_dataset_mask.py

@@ -42,6 +42,10 @@ alldata = np.array([[1, 1, 1],
                     [1, 1, 1],
                     [1, 1, 1]]).astype('uint8') * 255
 
+# boundless window ((1, 4, (1, 4))
+alp_shift_lr = np.array([[1, 1, 0],
+                         [0, 1, 0],
+                         [0, 0, 0]]).astype('uint8') * 255
 
 @pytest.fixture(scope='function')
 def tiffs(tmpdir):
@@ -159,3 +163,21 @@ def test_rgba_msk(tiffs):
     with rasterio.open(str(tiffs.join('rgba_msk.tif'))) as src:
         # mask takes precendent over alpha
         assert np.array_equal(src.dataset_mask(), msk)
+
+def test_args(tiffs):
+    with rasterio.open(str(tiffs.join('rgb_ndv.tif'))) as src:
+        res = src.dataset_mask()
+        assert np.array_equal(res , alp)
+        # positional args ignored
+        other = src.dataset_mask('FOO')
+        assert np.array_equal(res, other)
+
+def test_kwargs(tiffs):
+    with rasterio.open(str(tiffs.join('rgb_ndv.tif'))) as src:
+        # window and boundless are passes along
+        other = src.dataset_mask(window=((1, 4), (1, 4)), boundless=True)
+        assert np.array_equal(alp_shift_lr, other)
+
+        # band indexes are not supported
+        with pytest.raises(TypeError):
+            src.dataset_mask(indexes=1)