Drop optional dependencies of Spack (#43081)

Remove dependency on `importlib_metadata` and `pkg_resources`, which can be problematic if the version in PYTHONPATH is incompatible with the interpreter Spack is running under.

lib/spack/llnl/util/lang.py

@@ -12,7 +12,6 @@
 import re
 import sys
 import traceback
-import warnings
 from datetime import datetime, timedelta
 from typing import Any, Callable, Iterable, List, Tuple
 
@@ -847,43 +846,25 @@ def __repr__(self):
 def get_entry_points(*, group: str):
     """Wrapper for ``importlib.metadata.entry_points``
 
-    Adapted from https://github.com/HypothesisWorks/hypothesis/blob/0a90ed6edf56319149956c7321d4110078a5c228/hypothesis-python/src/hypothesis/entry_points.py
-
     Args:
-        group (str): the group of entry points to select
+        group: entry points to select
 
     Returns:
-        EntryPoints for ``group``
-
+        EntryPoints for ``group`` or empty list if unsupported
     """
 
     try:
-        try:
-            from importlib import metadata as importlib_metadata  # type: ignore  # novermin
-        except ImportError:
-            import importlib_metadata  # type: ignore  # mypy thinks this is a redefinition
-        try:
-            entry_points = importlib_metadata.entry_points(group=group)
-        except TypeError:
-            # Prior to Python 3.10, entry_points accepted no parameters and always
-            # returned a dictionary of entry points, keyed by group.  See
-            # https://docs.python.org/3/library/importlib.metadata.html#entry-points
-            entry_points = importlib_metadata.entry_points().get(group, [])
-        yield from entry_points
+        import importlib.metadata  # type: ignore  # novermin
     except ImportError:
-        # But if we're not on Python >= 3.8 and the importlib_metadata backport
-        # is not installed, we fall back to pkg_resources anyway.
-        try:
-            import pkg_resources  # type: ignore
-        except ImportError:
-            warnings.warn(
-                "Under Python <= 3.7, Spack requires either the importlib_metadata "
-                "or setuptools package in order to load extensions via entrypoints.",
-                ImportWarning,
-            )
-            yield from ()
-        else:
-            yield from pkg_resources.iter_entry_points(group)
+        return []
+
+    try:
+        return importlib.metadata.entry_points(group=group)
+    except TypeError:
+        # Prior to Python 3.10, entry_points accepted no parameters and always
+        # returned a dictionary of entry points, keyed by group.  See
+        # https://docs.python.org/3/library/importlib.metadata.html#entry-points
+        return importlib.metadata.entry_points().get(group, [])
 
 
 def load_module_from_file(module_name, module_path):

lib/spack/spack/test/entry_points.py

@@ -8,6 +8,8 @@
 
 import pytest
 
+import llnl.util.lang
+
 import spack.config
 import spack.extensions
 
@@ -64,24 +66,12 @@ def entry_points(group=None):
 
 
 @pytest.fixture()
-def mock_entry_points(tmp_path, monkeypatch):
+def mock_get_entry_points(tmp_path, monkeypatch):
     entry_points = entry_points_factory(tmp_path)
-    try:
-        try:
-            import importlib.metadata as importlib_metadata  # type: ignore # novermin
-        except ImportError:
-            import importlib_metadata
-        monkeypatch.setattr(importlib_metadata, "entry_points", entry_points)
-    except ImportError:
-        try:
-            import pkg_resources  # type: ignore
-        except ImportError:
-            return
-        monkeypatch.setattr(pkg_resources, "iter_entry_points", entry_points)
+    monkeypatch.setattr(llnl.util.lang, "get_entry_points", entry_points)
 
 
-@pytest.mark.skipif(sys.version_info[:2] < (3, 8), reason="Python>=3.8 required")
-def test_spack_entry_point_config(tmp_path, mock_entry_points):
+def test_spack_entry_point_config(tmp_path, mock_get_entry_points):
     """Test config scope entry point"""
     config_paths = dict(spack.config.config_paths_from_entry_points())
     config_path = config_paths.get("plugin-mypackage_config")
@@ -94,8 +84,7 @@ def test_spack_entry_point_config(tmp_path, mock_entry_points):
     assert config.get("config:install_tree:root", scope="plugin-mypackage_config") == "/spam/opt"
 
 
-@pytest.mark.skipif(sys.version_info[:2] < (3, 8), reason="Python>=3.8 required")
-def test_spack_entry_point_extension(tmp_path, mock_entry_points):
+def test_spack_entry_point_extension(tmp_path, mock_get_entry_points):
     """Test config scope entry point"""
     my_ext = tmp_path / "spack/spack-myext"
     extensions = spack.extensions.get_extension_paths()
@@ -110,3 +99,16 @@ def test_spack_entry_point_extension(tmp_path, mock_entry_points):
     assert os.path.samefile(root, my_ext)
     module = spack.extensions.get_module("spam")
     assert module is not None
+
+
+@pytest.mark.skipif(sys.version_info[:2] < (3, 8), reason="Python>=3.8 required")
+def test_llnl_util_lang_get_entry_points(tmp_path, monkeypatch):
+    import importlib.metadata  # type: ignore # novermin
+
+    monkeypatch.setattr(importlib.metadata, "entry_points", entry_points_factory(tmp_path))
+
+    entry_points = list(llnl.util.lang.get_entry_points(group="spack.config"))
+    assert isinstance(entry_points[0], MockConfigEntryPoint)
+
+    entry_points = list(llnl.util.lang.get_entry_points(group="spack.extensions"))
+    assert isinstance(entry_points[0], MockExtensionsEntryPoint)