pathfinding docstrings: multi_stop_search lacks an Examples section, malformed sourcecode directive, NaN impassability undocumented

[brendancol]

A documentation audit of xrspatial/pathfinding.py (public functions: a_star_search, multi_stop_search) found three gaps. All fixes are doc-only; no behavior changes.

1. multi_stop_search has no Examples section

Structure check (same pattern as test_multispectral.py::test_docstring_params_match_signature), run 2026-07-08 against main:

multi_stop_search
  section Parameters: present
  section Returns: present
  section Examples: MISSING
  >>> lines: 0

a_star_search has a 13-line example; its sibling has none. A runnable example for the fix, verified on this host:

import numpy as np
import xarray as xr
from xrspatial import multi_stop_search

agg = xr.DataArray(np.array([
    [0, 1, 0, 0],
    [1, 1, 0, 0],
    [0, 1, 2, 2],
    [1, 0, 2, 0],
    [0, 2, 2, 2]
], dtype=np.float64), dims=['lat', 'lon'])
height, width = agg.shape
agg['lon'] = np.linspace(0, width - 1, width)
agg['lat'] = np.linspace(height - 1, 0, height)

path_agg = multi_stop_search(agg, [(3, 0), (1, 2), (0, 1)],
                             barriers=[0], x='lon', y='lat')
path_agg.attrs['waypoint_order']   # [(3, 0), (1, 2), (0, 1)]
path_agg.attrs['segment_costs']    # [2.8284271247461903, 1.4142135623730951]
path_agg.attrs['total_cost']       # 4.242640687119286

2. a_star_search example block uses a malformed rst directive

xrspatial/pathfinding.py:902:

... sourcecode:: python

Three dots instead of two. Every other module writes .. sourcecode:: python; this is the only three-dot occurrence in the codebase:

$ grep -rn '\.\.\. sourcecode' xrspatial/*.py
xrspatial/pathfinding.py:902:    ... sourcecode:: python

With three dots it is not a directive, so the rendered API page shows the line as literal text instead of starting a code block. The example itself runs fine when copy-pasted (verified).

3. NaN cells are impassable, but neither docstring says so

_is_not_crossable (pathfinding.py:68-77) treats any NaN surface cell as a barrier regardless of the barriers list, and test_pathfinding.py pins this (input_data_with_nans, the snap tests start on NaN pixels). The friction NaN rule is documented ("NaN or <= 0 marks impassable barriers"), but the surface NaN rule appears in neither public docstring. A user with a NaN-nodata raster cannot tell from the docs that nodata cells are automatically excluded from paths, even with the default barriers=[].

Minor, fixed in passing

• y: str, default='y' in a_star_search's Parameters section is missing the space before the colon that numpydoc entries use (y : str).

Not duplicated here

The wrong surface description ("values to bin") and the empty connectivity description are already tracked in #3644 (item 3).

Other checks came back clean: docstring parameters match both signatures exactly, both functions are listed in docs/source/reference/pathfinding.rst, and the backend-support table in a_star_search's docstring was verified by running all four backends (numpy, cupy, dask+numpy, dask+cupy) on this host.