test and fix empty xindexes repr

xarray/core/formatting.py

@@ -357,7 +357,7 @@ def summarize_attr(key, value, col_width=None):
 
 
 def _calculate_col_width(col_items):
-    max_name_length = max(len(str(s)) for s in col_items) if col_items else 0
+    max_name_length = max((len(str(s)) for s in col_items), default=0)
     col_width = max(max_name_length, 7) + 6
     return col_width
 

xarray/tests/test_formatting.py

@@ -773,3 +773,33 @@ def __array__(self, dtype=None):
     # These will crash if var.data are converted to numpy arrays:
     var.__repr__()
     var._repr_html_()
+
+
+@pytest.mark.parametrize("as_dataset", (False, True))
+def test_format_xindexes_none(as_dataset):
+    # ensure repr for empty xindexes can be displayed #8367
+
+    expected = """\
+    Indexes:
+        *empty*"""
+    expected = dedent(expected)
+
+    obj = xr.DataArray()
+    obj = obj._to_temp_dataset() if as_dataset else obj  # type: ignore[assignment]
+
+    actual = obj.xindexes.__repr__()
+    assert actual == expected
+
+
+@pytest.mark.parametrize("as_dataset", (False, True))
+def test_format_xindexes(as_dataset):
+    expected = """\
+    Indexes:
+        x        PandasIndex"""
+    expected = dedent(expected)
+
+    obj = xr.DataArray([1], coords={"x": [1]})
+    obj = obj._to_temp_dataset() if as_dataset else obj  # type: ignore[assignment]
+
+    actual = obj.xindexes.__repr__()
+    assert actual == expected