[PATCH] demandimport: fix level passed to loader of sub-modules

[Pierre-Yves David]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1446380349 -32400
#      Sun Nov 01 21:19:09 2015 +0900
# Node ID 72cc3d5bfdaa086fe184b2ceb2cb7766434fc144
# Parent  1cbf144fd8a170b2a5e2a7f68357368c5793d7a4
# Available At http://hg.netv6.net/marmoute-wip/mercurial/
#              hg pull http://hg.netv6.net/marmoute-wip/mercurial/ -r 72cc3d5bfdaa
demandimport: fix level passed to loader of sub-modules

As the fromlist gives the names of sub-modules, they should be searched in
the parent directory of the package's __init__.py, which is level=1.

I got the following error by rewriting hgweb to use absolute_import, where
the "mercurial" package is referenced as ".." (level=2):

  ValueError: Attempted relative import beyond toplevel package

I know little about the import mechanism, but this change seems correct.
Before this patch, the following code did import the os module with no error:

  from mercurial import demandimport
  demandimport.enable()
  from mercurial import os
  print os.name

diff --git a/mercurial/demandimport.py b/mercurial/demandimport.py
--- a/mercurial/demandimport.py
+++ b/mercurial/demandimport.py
@@ -162,19 +162,19 @@ def _demandimport(name, globals=None, lo
         # so modern Mercurial code will have level >= 0.
 
         # The name of the module the import statement is located in.
         globalname = globals.get('__name__')
 
-        def processfromitem(mod, attr, **kwargs):
+        def processfromitem(mod, attr):
             """Process an imported symbol in the import statement.
 
             If the symbol doesn't exist in the parent module, it must be a
             module. We set missing modules up as _demandmod instances.
             """
             symbol = getattr(mod, attr, nothing)
             if symbol is nothing:
-                symbol = _demandmod(attr, mod.__dict__, locals, **kwargs)
+                symbol = _demandmod(attr, mod.__dict__, locals, level=1)
                 setattr(mod, attr, symbol)
 
             # Record the importing module references this symbol so we can
             # replace the symbol with the actual module instance at load
             # time.
@@ -192,11 +192,11 @@ def _demandimport(name, globals=None, lo
                                     fromlist, level)
 
             mod = _hgextimport(_origimport, name, globals, locals, level=level)
 
             for x in fromlist:
-                processfromitem(mod, x, level=level)
+                processfromitem(mod, x)
 
             return mod
 
         # But, we still need to support lazy loading of standard library and 3rd
         # party modules. So handle level == -1.