demandimport: move HGDEMANDIMPORT test to __init__.py

The logic is now shared between demandimport{2,3}.

Differential Revision: https://phab.mercurial-scm.org/D445

hgdemandimport/__init__.py

@@ -13,6 +13,7 b''
 
 from __future__ import absolute_import
 
+import os
 import sys
 
 if sys.version_info[0] >= 3:
@@ -68,6 +69,9 b' demandimport.init(ignore)'
 
 # Re-export.
 isenabled = demandimport.isenabled
-enable = demandimport.enable
 disable = demandimport.disable
 deactivated = demandimport.deactivated
+
+def enable():
+    if os.environ.get('HGDEMANDIMPORT') != 'disable':
+        demandimport.enable()

hgdemandimport/demandimportpy2.py

@@ -28,7 +28,6 b' from __future__ import absolute_import'
 
 import __builtin__ as builtins
 import contextlib
-import os
 import sys
 
 contextmanager = contextlib.contextmanager
@@ -285,8 +284,7 b' def isenabled():'
 
 def enable():
     "enable global demand-loading of modules"
-    if os.environ.get('HGDEMANDIMPORT') != 'disable':
-        builtins.__import__ = _demandimport
+    builtins.__import__ = _demandimport
 
 def disable():
     "disable global demand-loading of modules"

hgdemandimport/demandimportpy3.py

@@ -27,7 +27,6 b' This also has some limitations compared '
 from __future__ import absolute_import
 
 import contextlib
-import os
 import sys
 
 import importlib.abc
@@ -81,8 +80,7 b' def disable():'
         pass
 
 def enable():
-    if os.environ.get('HGDEMANDIMPORT') != 'disable':
-        sys.path_hooks.insert(0, _makefinder)
+    sys.path_hooks.insert(0, _makefinder)
 
 @contextlib.contextmanager
 def deactivated():