Test concat of dimension coordinate not backed by an index

README.md

@@ -23,6 +23,7 @@ Currently you need to clone VirtualiZarr and install it locally:
 git clone virtualizarr
 pip install -e .
 ```
+You will also need a specific branch of xarray in order for concatenation without indexes to work. (See [this comment](https://github.com/TomNicholas/VirtualiZarr/issues/14#issuecomment-2018369470).) You may want to install the dependencies using the `virtualizarr/ci/environment.yml` conda file, which includes the specific branch of xarray required.
 
 ### Usage
 

ci/environment.yml

@@ -15,4 +15,4 @@ dependencies:
   - ujson
   - pydantic
   - pip:
-      - xarray>=2024.02.0.dev0
+      - git+https://github.com/TomNicholas/xarray.git@concat-no-indexes#egg=xarray

virtualizarr/tests/test_xarray.py

@@ -72,6 +72,7 @@ def test_equals(self):
         assert not ds1.equals(ds3)
 
 
+# TODO refactor these tests by making some fixtures
 class TestConcat:
     def test_concat_along_existing_dim(self):
         # both manifest arrays in this example have the same zarray properties
@@ -164,3 +165,53 @@ def test_concat_along_new_dim(self):
         assert result.data.zarray.fill_value == zarray.fill_value
         assert result.data.zarray.order == zarray.order
         assert result.data.zarray.zarr_format == zarray.zarr_format
+
+    def test_concat_dim_coords_along_existing_dim(self):
+        # Tests that dimension coordinates don't automatically get new indexes on concat
+        # See https://github.com/pydata/xarray/issues/8871
+
+        # both manifest arrays in this example have the same zarray properties
+        zarray = ZArray(
+            chunks=(10,),
+            compressor="zlib",
+            dtype=np.dtype("int32"),
+            fill_value=0.0,
+            filters=None,
+            order="C",
+            shape=(20,),
+            zarr_format=2,
+        )
+
+        chunks_dict1 = {
+            "0": {"path": "foo.nc", "offset": 100, "length": 100},
+            "1": {"path": "foo.nc", "offset": 200, "length": 100},
+        }
+        manifest1 = ChunkManifest(entries=chunks_dict1)
+        marr1 = ManifestArray(zarray=zarray, chunkmanifest=manifest1)
+        coords = xr.Coordinates({"t": (["t"], marr1)}, indexes={})
+        ds1 = xr.Dataset(coords=coords)
+
+        chunks_dict2 = {
+            "0": {"path": "foo.nc", "offset": 300, "length": 100},
+            "1": {"path": "foo.nc", "offset": 400, "length": 100},
+        }
+        manifest2 = ChunkManifest(entries=chunks_dict2)
+        marr2 = ManifestArray(zarray=zarray, chunkmanifest=manifest2)
+        coords = xr.Coordinates({"t": (["t"], marr2)}, indexes={})
+        ds2 = xr.Dataset(coords=coords)
+
+        result = xr.concat([ds1, ds2], dim="t")["t"]
+
+        assert result.shape == (40,)
+        assert result.chunks == (10,)
+        assert result.data.manifest.dict() == {
+            "0": {"path": "foo.nc", "offset": 100, "length": 100},
+            "1": {"path": "foo.nc", "offset": 200, "length": 100},
+            "2": {"path": "foo.nc", "offset": 300, "length": 100},
+            "3": {"path": "foo.nc", "offset": 400, "length": 100},
+        }
+        assert result.data.zarray.compressor == zarray.compressor
+        assert result.data.zarray.filters == zarray.filters
+        assert result.data.zarray.fill_value == zarray.fill_value
+        assert result.data.zarray.order == zarray.order
+        assert result.data.zarray.zarr_format == zarray.zarr_format