Make list_chunkmanagers more resilient to broken entrypoints (#8736)

* Make list_chunkmanagers more resilient to broken entrypoints

As I'm a developing my custom chunk manager, I'm often checking out
between my development branch and production branch breaking the
entrypoint.

This made xarray impossible to import unless I re-ran `pip install -e . -vv`
which is somewhat tiring.

* Type hint untyped test function to appease mypy

* Try to return something to help mypy

---------

Co-authored-by: Tom Nicholas <tom@cworthy.org>
Co-authored-by: Illviljan <14371165+Illviljan@users.noreply.github.com>

xarray/core/utils.py

@@ -1106,10 +1106,10 @@ def find_stack_level(test_mode=False) -> int:
     return n
 
 
-def emit_user_level_warning(message, category=None):
+def emit_user_level_warning(message, category=None) -> None:
     """Emit a warning at the user level by inspecting the stack trace."""
     stacklevel = find_stack_level()
-    warnings.warn(message, category=category, stacklevel=stacklevel)
+    return warnings.warn(message, category=category, stacklevel=stacklevel)
 
 
 def consolidate_dask_from_array_kwargs(

xarray/namedarray/parallelcompat.py

@@ -15,6 +15,7 @@
 
 import numpy as np
 
+from xarray.core.utils import emit_user_level_warning
 from xarray.namedarray.pycompat import is_chunked_array
 
 if TYPE_CHECKING:
@@ -73,9 +74,15 @@ def load_chunkmanagers(
 ) -> dict[str, ChunkManagerEntrypoint[Any]]:
     """Load entrypoints and instantiate chunkmanagers only once."""
 
-    loaded_entrypoints = {
-        entrypoint.name: entrypoint.load() for entrypoint in entrypoints
-    }
+    loaded_entrypoints = {}
+    for entrypoint in entrypoints:
+        try:
+            loaded_entrypoints[entrypoint.name] = entrypoint.load()
+        except ModuleNotFoundError as e:
+            emit_user_level_warning(
+                f"Failed to load chunk manager entrypoint {entrypoint.name} due to {e}. Skipping.",
+            )
+            pass
 
     available_chunkmanagers = {
         name: chunkmanager()

xarray/tests/test_parallelcompat.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from importlib.metadata import EntryPoint
 from typing import Any
 
 import numpy as np
@@ -13,6 +14,7 @@
     get_chunked_array_type,
     guess_chunkmanager,
     list_chunkmanagers,
+    load_chunkmanagers,
 )
 from xarray.tests import has_dask, requires_dask
 
@@ -218,3 +220,13 @@ def test_raise_on_mixed_array_types(self, register_dummy_chunkmanager) -> None:
 
         with pytest.raises(TypeError, match="received multiple types"):
             get_chunked_array_type(*[dask_arr, dummy_arr])
+
+
+def test_bogus_entrypoint() -> None:
+    # Create a bogus entry-point as if the user broke their setup.cfg
+    # or is actively developing their new chunk manager
+    entry_point = EntryPoint(
+        "bogus", "xarray.bogus.doesnotwork", "xarray.chunkmanagers"
+    )
+    with pytest.warns(UserWarning, match="Failed to load chunk manager"):
+        assert len(load_chunkmanagers([entry_point])) == 0