fix: handle 0-length arrays

Author: d-v-b

src/zarr/core/chunk_grids.py

@@ -695,6 +695,8 @@ def normalize_chunks_1d(chunks: int | None | Iterable[int], span: int) -> tuple[
     if isinstance(chunks, int):
         if chunks <= 0:
             raise ValueError(f"Chunk size must be positive, got {chunks}")
+        if span == 0:
+            return (chunks,)
         n = ceildiv(span, chunks)
         return tuple(chunks for _ in range(n))
     else:

tests/test_chunk_grids.py

@@ -45,6 +45,10 @@ def test_guess_chunks(shape: tuple[int, ...], itemsize: int) -> None:
         # sentinel values
         (-1, (100,), ((100,),)),
         ((30, -1, None), (100, 20, 10), ((30, 30, 30, 30), (20,), (10,))),
+        # zero-length dimensions preserve the declared chunk size
+        (10, (0,), ((10,),)),
+        ((5, 10), (0, 100), ((5,), (10,) * 10)),
+        ((5, 10), (20, 0), ((5, 5, 5, 5), (10,))),
     ],
 )
 def test_normalize_chunks(