Fix NamedArray html repr crashing (pydata#9553)

* Fix namedarray repr crashing

* fix mypy

xarray/core/formatting.py

@@ -303,7 +303,7 @@ def inline_variable_array_repr(var, max_width):
     """Build a one-line summary of a variable's data."""
     if hasattr(var._data, "_repr_inline_"):
         return var._data._repr_inline_(max_width)
-    if var._in_memory:
+    if getattr(var, "_in_memory", False):
         return format_array_flat(var, max_width)
     dask_array_type = array_type("dask")
     if isinstance(var._data, dask_array_type):

xarray/tests/test_namedarray.py

@@ -591,3 +591,15 @@ def test_broadcast_to_errors(
     def test_warn_on_repeated_dimension_names(self) -> None:
         with pytest.warns(UserWarning, match="Duplicate dimension names"):
             NamedArray(("x", "x"), np.arange(4).reshape(2, 2))
+
+
+def test_repr() -> None:
+    x: NamedArray[Any, np.dtype[np.uint64]]
+    x = NamedArray(("x",), np.array([0], dtype=np.uint64))
+
+    # Reprs should not crash:
+    r = x.__repr__()
+    x._repr_html_()
+
+    # Basic comparison:
+    assert r == "<xarray.NamedArray (x: 1)> Size: 8B\narray([0], dtype=uint64)"