What happened?

Got an error when calling data_tree.chunk('auto')

This is pretty frustrating, when xr.open_datatree supports it. I would expect both to be equivalent.

What did you expect to happen?

I expect it to succeed, and be equivalent to chunking the dataset, or opening the datatree with the chunks="auto" argument.

Both the type of the argument andthe docs imply this should work.

Minimal Complete Verifiable Example

# /// script
# requires-python = ">=3.11"
# dependencies = [
#   "xarray[complete]@git+https://github.com/pydata/xarray.git@main",
# ]
# ///
#
# This script automatically imports the development branch of xarray to check for issues.
# Please delete this header if you have _not_ tested this script with `uv run`!

import xarray as xr
xr.show_versions()
# your reproducer code ...

import numpy as np
import xarray as xr

ds = xr.Dataset({"a": (("x", "y"), np.zeros((10, 5)))})
dt = xr.DataTree(ds)

ds.chunk("auto")  # works
dt.chunk("auto")  # TypeError

Steps to reproduce

uv run the above script.

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

Traceback (most recent call last):
       File "/root/timaeus/.claude/worktrees/auto-chunking/repro_script.py", line 23, in <module>
         dt.chunk("auto")  # TypeError
         ^^^^^^^^^^^^^^^^
       File "/.uv/cache/environments-v2/repro-script-8f1b2638dcd6a5aa/lib/python3.11/site-packages/xarray/core/datatree.py", line 2655, in
     chunk
         raise TypeError(
     TypeError: invalid type for chunks: <class 'str'>. Only mappings are supported.

Anything else we need to know?

I've worked aorund with
dt.map_over_datasets(lambda ds: ds.chunk("auto"))
which I think is equivalent?

Environment