Fix indexing zero-sized dimension (#761)

Author: tomwhite

cubed/core/indexing.py

@@ -87,7 +87,8 @@ def merged_chunk_len_for_indexer(ia, c):
         # empty output case
         from cubed.array_api.creation_functions import empty
 
-        out = empty(shape, dtype=x.dtype, chunks=x.chunksize, spec=x.spec)
+        chunks = tuple(c for c in x.chunksize if c > 0)
+        out = empty(shape, dtype=x.dtype, chunks=chunks, spec=x.spec)
     else:
         dtype = x.dtype
         chunks = tuple(

cubed/tests/test_array_api.py

@@ -357,6 +357,21 @@ def test_index_2d_step(spec, shape, chunks, ind, new_chunks_expected):
     assert b.chunks == new_chunks_expected
 
 
+@pytest.mark.parametrize(
+    ("shape", "chunks", "ind"),
+    [
+        ((0, 2), (0, 2), (slice(None), 0)),
+        ((0, 2), (1, 2), (slice(None), 0)),
+        ((2, 0), (2, 0), (0, slice(None))),
+        ((2, 0), (2, 1), (0, slice(None))),
+    ],
+)
+def test_index_zero_dim(shape, chunks, ind):
+    a = xp.ones(shape, chunks=chunks)
+    b = a[ind]
+    assert_array_equal(b.compute(), np.ones(shape)[ind])
+
+
 def test_index_slice_unsupported_step(spec):
     a = xp.arange(12, chunks=(4,), spec=spec)
     with pytest.raises(NotImplementedError):