Rely on passthrough to designate a wrapper for its side effect.

Author: jaraco

importlib_metadata/__init__.py

@@ -35,7 +35,7 @@
     NullFinder,
     install,
 )
-from ._functools import method_cache, noop, pass_none
+from ._functools import method_cache, noop, pass_none, passthrough
 from ._itertools import always_iterable, bucket, unique_everseen
 from ._meta import PackageMetadata, SimplePath
 from ._typing import md_none
@@ -787,6 +787,7 @@ def find_distributions(self, context=Context()) -> Iterable[Distribution]:
         """
 
 
+@passthrough
 def _clear_after_fork(cached):
     """Ensure ``func`` clears cached state after ``fork`` when supported.
 
@@ -798,7 +799,6 @@ def _clear_after_fork(cached):
     on its own cache.
     """
     getattr(os, 'register_at_fork', noop)(after_in_child=cached.cache_clear)
-    return cached
 
 
 class FastPath:
@@ -817,7 +817,7 @@ class FastPath:
     True
     """
 
-    @_clear_after_fork
+    @_clear_after_fork  # type: ignore[misc]
     @functools.lru_cache()
     def __new__(cls, root):
         return super().__new__(cls)

importlib_metadata/_functools.py

@@ -1,5 +1,6 @@
 import functools
 import types
+from typing import Callable, TypeVar
 
 
 # from jaraco.functools 3.3
@@ -111,3 +112,24 @@ def noop(*args, **kwargs):
 
     >>> noop(1, 2, three=3)
     """
+
+
+_T = TypeVar('_T')
+
+
+# From jaraco.functools 4.4
+def passthrough(func: Callable[..., object]) -> Callable[[_T], _T]:
+    """
+    Wrap the function to always return the first parameter.
+
+    >>> passthrough(print)('3')
+    3
+    '3'
+    """
+
+    @functools.wraps(func)
+    def wrapper(first: _T, *args, **kwargs) -> _T:
+        func(first, *args, **kwargs)
+        return first
+
+    return wrapper  # type: ignore[return-value]