Error when broadcast given int

What happened?

Unhelpful error raised by xr.broadcast when supplied with an int.

What did you expect to happen?

The broadcast to succeed I think?

Minimal Complete Verifiable Example

In [1]: import xarray as xr

In [2]: da = xr.DataArray([5, 4], dims='x')

In [3]: xr.broadcast(da, 1)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[3], line 1
----> 1 xr.broadcast(da, 1)

File ~/miniconda3/envs/xrdev3.9/lib/python3.9/site-packages/xarray/core/alignment.py:1049, in broadcast(exclude, *args)
   1047 if exclude is None:
   1048     exclude = set()
-> 1049 args = align(*args, join="outer", copy=False, exclude=exclude)
   1051 dims_map, common_coords = _get_broadcast_dims_map_common_coords(args, exclude)
   1052 result = [_broadcast_helper(arg, exclude, dims_map, common_coords) for arg in args]

File ~/miniconda3/envs/xrdev3.9/lib/python3.9/site-packages/xarray/core/alignment.py:772, in align(join, copy, indexes, exclude, fill_value, *objects)
    576 """
    577 Given any number of Dataset and/or DataArray objects, returns new
    578 objects with aligned indexes and dimension sizes.
   (...)
    762 
    763 """
    764 aligner = Aligner(
    765     objects,
    766     join=join,
   (...)
    770     fill_value=fill_value,
    771 )
--> 772 aligner.align()
    773 return aligner.results

File ~/miniconda3/envs/xrdev3.9/lib/python3.9/site-packages/xarray/core/alignment.py:556, in Aligner.align(self)
    553     self.results = (obj.copy(deep=self.copy),)
    554     return
--> 556 self.find_matching_indexes()
    557 self.find_matching_unindexed_dims()
    558 self.assert_no_index_conflict()

File ~/miniconda3/envs/xrdev3.9/lib/python3.9/site-packages/xarray/core/alignment.py:262, in Aligner.find_matching_indexes(self)
    259 objects_matching_indexes = []
    261 for obj in self.objects:
--> 262     obj_indexes, obj_index_vars = self._normalize_indexes(obj.xindexes)
    263     objects_matching_indexes.append(obj_indexes)
    264     for key, idx in obj_indexes.items():

AttributeError: 'int' object has no attribute 'xindexes'

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.

Relevant log output

No response

Anything else we need to know?

This clearly has something to do with a change in the flexible indexes refactor, as it complains about .xindexes not being present. @benbovy

Environment

The main branch

Start by reproducing the MVCE with xr.broadcast(da, 1), then inspect xarray/core/alignment.py around broadcast(), align(), and Aligner.find_matching_indexes(), which the traceback identifies. Determine the intended handling of scalar integers and add coverage for this case; done means the example no longer raises the shown AttributeError and the behavior matches the project’s intended broadcast semantics.