From patchwork Sat Aug 13 10:15:25 2016
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Subject: [3, of, 5,
 RFC] policy: add helper to import cpy/pure module selectively
From: Yuya Nishihara <yuya@tcha.org>
X-Patchwork-Id: 16270
Message-Id: <8bb0a9223bce791bae9e.1471083325@mimosa>
To: mercurial-devel@mercurial-scm.org
Date: Sat, 13 Aug 2016 19:15:25 +0900

# HG changeset patch
# User Yuya Nishihara <yuya@tcha.org>
# Date 1470969017 -32400
#      Fri Aug 12 11:30:17 2016 +0900
# Node ID 8bb0a9223bce791bae9e6a07238d6b9722e5577a
# Parent  bda4422fc315b54356ba1949e5ba861dd2660e86
policy: add helper to import cpy/pure module selectively

Unfortunately, __import__() nor getattr() does not take bytes, and globals()
is a dict keyed by unicodes on Python 3. uimportvars() is a unicode API to
comply with their requirement. I really hated mixing bytes and unicodes, but
bytes version of importvars() would be useless.

Nit: KeyError would be raised for invalid HGMODULEPOLICY. What should we
do in that case?

diff --git a/mercurial/policy.py b/mercurial/policy.py
--- a/mercurial/policy.py
+++ b/mercurial/policy.py
@@ -23,6 +23,14 @@ policy = 'c'
 policynoc = ('cffi', 'cffi-allow', 'py')
 policynocffi = ('c', 'py')
 
+_upackagetable = {
+    'c': [u'cpy'],
+    'allow': [u'cpy', u'pure'],
+    'cffi': [u'pure'],  # TODO: [u'cffi']
+    'cffi-allow': [u'pure'],  # TODO: [u'cffi', u'pure']
+    'py': [u'pure'],
+}
+
 try:
     from . import __modulepolicy__
     policy = __modulepolicy__.modulepolicy
@@ -43,3 +51,24 @@ if sys.version_info[0] >= 3:
 
 # Environment variable can always force settings.
 policy = os.environ.get('HGMODULEPOLICY', policy)
+
+def _uexportedvars(mod):
+    """Build dict of public names to simulate 'from mod import *'"""
+    modvars = vars(mod)
+    if u'__all__' in modvars:
+        allnames = modvars[u'__all__']
+        return dict((k, v) for k, v in modvars.items() if k in allnames)
+    return dict((k, v) for k, v in modvars.items() if not k.startswith(u'_'))
+
+def uimportvars(uname):
+    """Import module according to policy and return exported vars"""
+    upkgnames = _upackagetable[policy]
+    for upkg in upkgnames:
+        try:
+            # pass globals() to resolve name relative to this module
+            mod = __import__(u'%s.%s' % (upkg, uname), globals(), level=1)
+            mod = getattr(mod, uname)
+            return _uexportedvars(mod)
+        except ImportError:
+            if upkg == upkgnames[-1]:
+                raise