unable to stack on IntervalIndex

[jmineau]

What happened?

Previously, in v2025.03.1 datasets were able to be stacked upon IntervalIndex dimensions. This is no longer the case. I now receive the following error:

TypeError: Cannot interpret 'interval[datetime64[ns], left]' as a data type

What did you expect to happen?

I expected to be able to stack on IntervalIndex dimensions as this was previous behavior.

Minimal Complete Verifiable Example

import numpy as np
import pandas as pd
import xarray as xr

t0 = pd.Timestamp('2024-01-01 00:00:00')
t1 = pd.Timestamp('2024-01-07 00:00:00')
dt = pd.Timedelta('1d')
t = pd.interval_range(start=t0, end=t1+dt, freq=dt, closed='left')

xmin = -112.15
xmax = -111.75
ymin = 40.45
ymax = 40.95
dx = dy = 0.05

x = np.arange(xmin, xmax + dx, dx)
y = np.arange(ymin, ymax + dy, dy)

ds = xr.Dataset(
    {
        'data': (['time', 'y', 'x'], np.random.rand(len(t), len(y), len(x))),
    },
    coords={
        'time': t,
        'y': y,
        'x': x,
    }
)

ds.stack(state=('time', 'y', 'x'))

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.
• Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

>>> ds.stack(state=('time', 'y', 'x'))
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    ds.stack(state=('time', 'y', 'x'))
    ~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/site-packages/xarray/core/dataset.py", line 2313, in __repr__
    return formatting.dataset_repr(self)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/reprlib.py", line 21, in wrapper
    result = user_function(self)
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/site-packages/xarray/core/formatting.py", line 752, in dataset_repr
    summary.append(coords_repr(ds.coords, col_width=col_width, max_rows=max_rows))
                   ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/site-packages/xarray/core/formatting.py", line 441, in coords_repr
    return _mapping_repr(
        coords,
    ...<5 lines>...
        max_rows=max_rows,
    )
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/site-packages/xarray/core/formatting.py", line 415, in _mapping_repr
    summarizer(k, v, col_width, **summarizer_kwargs[k])
    ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/site-packages/xarray/core/formatting.py", line 351, in summarize_variable
    values_str = inline_variable_array_repr(variable, values_width)
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/site-packages/xarray/core/formatting.py", line 305, in inline_variable_array_repr
    return var._data._repr_inline_(max_width)
           ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/site-packages/xarray/core/indexing.py", line 2057, in _repr_inline_
    return format_array_flat(self._get_array_subset(), max_width)
                             ~~~~~~~~~~~~~~~~~~~~~~^^
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/site-packages/xarray/core/indexing.py", line 2049, in _get_array_subset
    return np.asarray(subset)
           ~~~~~~~~~~^^^^^^^^
  File "/uufs/chpc.utah.edu/common/home/u6036966/software/python/miniforge3/envs/xarray_interval/lib/python3.13/site-packages/xarray/core/indexing.py", line 1983, in __array__
    return np.asarray(
           ~~~~~~~~~~^
        self.array.get_level_values(self.level).values, dtype=dtype
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
TypeError: Cannot interpret 'interval[datetime64[ns], left]' as a data type

Anything else we need to know?

This seems similar to #10312

Environment

>>> xr.show_versions()

INSTALLED VERSIONS

commit: None
python: 3.13.5 | packaged by conda-forge | (main, Jun 16 2025, 08:27:50) [GCC 13.3.0]
python-bits: 64
OS: Linux
OS-release: 4.18.0-553.44.1.el8_10.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: None
libnetcdf: None

xarray: 2025.6.1
pandas: 2.3.0
numpy: 2.3.0
scipy: None
netCDF4: None
pydap: None
h5netcdf: None
h5py: None
zarr: None
cftime: None
nc_time_axis: None
iris: None
bottleneck: None
dask: None
distributed: None
matplotlib: None
cartopy: None
seaborn: None
numbagg: None
fsspec: None
cupy: None
pint: None
sparse: None
flox: None
numpy_groupies: None
setuptools: None
pip: 25.1.1
conda: None
pytest: None
mypy: None
IPython: None
sphinx: None

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