Fix a bug when setting complete chunks

Closes #2849

Author: dcherian

src/zarr/core/codec_pipeline.py

@@ -296,17 +296,6 @@ def _merge_chunk_array(
         is_complete_chunk: bool,
         drop_axes: tuple[int, ...],
     ) -> NDBuffer:
-        if is_complete_chunk and value.shape == chunk_spec.shape:
-            return value
-        if existing_chunk_array is None:
-            chunk_array = chunk_spec.prototype.nd_buffer.create(
-                shape=chunk_spec.shape,
-                dtype=chunk_spec.dtype,
-                order=chunk_spec.order,
-                fill_value=fill_value_or_default(chunk_spec),
-            )
-        else:
-            chunk_array = existing_chunk_array.copy()  # make a writable copy
         if chunk_selection == () or is_scalar(value.as_ndarray_like(), chunk_spec.dtype):
             chunk_value = value
         else:
@@ -320,6 +309,20 @@ def _merge_chunk_array(
                     for idx in range(chunk_spec.ndim)
                 )
                 chunk_value = chunk_value[item]
+        if is_complete_chunk:
+            # TODO: For the last chunk, we could have is_complete_chunk=True
+            #       that is smaller than the chunk_spec.shape but this throws
+            #       an error in the _decode_single
+            return chunk_value
+        if existing_chunk_array is None:
+            chunk_array = chunk_spec.prototype.nd_buffer.create(
+                shape=chunk_spec.shape,
+                dtype=chunk_spec.dtype,
+                order=chunk_spec.order,
+                fill_value=fill_value_or_default(chunk_spec),
+            )
+        else:
+            chunk_array = existing_chunk_array.copy()  # make a writable copy
         chunk_array[chunk_selection] = chunk_value
         return chunk_array
 

tests/test_array.py

@@ -829,6 +829,32 @@ def test_append_bad_shape(store: MemoryStore, zarr_format: ZarrFormat) -> None:
         z.append(b)
 
 
+def test_append_shape_not_equals_chunk_shape() -> None:
+    # regression test for GH2849
+    g = zarr.open("foo.zarr", zarr_format=3, mode="w")
+    g["bar"] = np.arange(3)
+
+    size = 4
+    data = [0, 1, 2, 3]
+    g["bar"].append(data)
+    assert (g["bar"][-size:] == data).all(), (g["bar"][-size:], data)
+
+    size = 3
+    data = [-1, -2, -3]
+    g["bar"].append(data)
+    assert (g["bar"][-size:] == data).all(), (g["bar"][-size:], data)
+
+    size = 2
+    data = [-10, -11]
+    g["bar"].append(data)
+    assert (g["bar"][-size:] == data).all(), (g["bar"][-size:], data)
+
+    size = 3
+    data = [-4, -5, -6]
+    g["bar"].append(data)
+    assert (g["bar"][-size:] == data).all(), (g["bar"][-size:], data)
+
+
 @pytest.mark.parametrize("store", ["memory"], indirect=True)
 @pytest.mark.parametrize("write_empty_chunks", [True, False])
 @pytest.mark.parametrize("fill_value", [0, 5])