[PATCH 3 of 3 v3] demandimport: reject contextlib._GeneratorContextManager on Py < 3.2

[timeless]

# HG changeset patch
# User timeless <timeless at mozdev.org>
# Date 1474429683 0
#      Wed Sep 21 03:48:03 2016 +0000
# Node ID 0070696439eab002f6dd32bcb40eb671daff800a
# Parent  adb54fd7d90f0ca607432ed7ae884da55ec427de
# Available At https://bitbucket.org/timeless/mercurial-crew
#              hg pull https://bitbucket.org/timeless/mercurial-crew -r 0070696439ea
demandimport: reject contextlib._GeneratorContextManager on Py < 3.2

decorator expects:
 from contextlib import _GeneratorContextManager
to throw an exception on python < 3.2 (issue5373).

We tell demandimport to throw it.

diff -r adb54fd7d90f -r 0070696439ea mercurial/demandimport.py
--- a/mercurial/demandimport.py	Wed Sep 21 18:58:54 2016 +0000
+++ b/mercurial/demandimport.py	Wed Sep 21 03:48:03 2016 +0000
@@ -313,6 +313,12 @@
 if os.name != 'nt':
     reject('distutils', 'msvc9compiler', ImportError, 'No module named _winreg')
 
+# decorator imported by ipython from pygments does an import which isn't
+# friendly to demandimport.
+if sys.version_info[0] < 3 or sys.version_info[1] < 2:
+    reject('contextlib', '_GeneratorContextManager',
+           ImportError, 'cannot import name _GeneratorContextManager')
+
 def isenabled():
     return builtins.__import__ == _demandimport
 
diff -r adb54fd7d90f -r 0070696439ea tests/test-demandimport.py
--- a/tests/test-demandimport.py	Wed Sep 21 18:58:54 2016 +0000
+++ b/tests/test-demandimport.py	Wed Sep 21 03:48:03 2016 +0000
@@ -71,6 +71,15 @@
 except ImportError:
     pass
 
+if sys.version_info[0] < 3 or sys.version_info[1] < 2:
+    try:
+        from contextlib import _GeneratorContextManager
+        print('contextlib._GeneratorContextManager needs to be an '
+              'immediate importerror on python <3.2')
+        _GeneratorContextManager.__doc__
+    except ImportError:
+        pass
+
 demandimport.disable()
 os.environ['HGDEMANDIMPORT'] = 'disable'
 # this enable call should not actually enable demandimport!