nocg: make the utility work are both a decorator and context manager

In some case, the context manager version will be simpler.

mercurial/util.py

@@ -35,6 +35,7 import traceback
 import warnings
 
 from typing import (
+    Any,
     Iterable,
     Iterator,
     List,
@@ -1812,7 +1813,7 def never(fn):
     return False
 
 
-def nogc(func):
+def nogc(func=None) -> Any:
     """disable garbage collector
 
     Python's garbage collector triggers a GC each time a certain number of
@@ -1825,16 +1826,28 def nogc(func):
     This garbage collector issue have been fixed in 2.7. But it still affect
     CPython's performance.
     """
-
-    def wrapper(*args, **kwargs):
+    if func is None:
+        return _nogc_context()
+    else:
+        return _nogc_decorator(func)
+
+
[e-mail]
+def _nogc_context():
         gcenabled = gc.isenabled()
         gc.disable()
         try:
-            return func(*args, **kwargs)
+        yield
         finally:
             if gcenabled:
                 gc.enable()
 
+
+def _nogc_decorator(func):
+    def wrapper(*args, **kwargs):
+        with _nogc_context():
+            return func(*args, **kwargs)
+
     return wrapper