win32: use Python's _winreg again

win32: use Python's _winreg again

This is a partial backout of f1fa8f481c7c.

f1fa8f481c7c switched win32.py to using ctypes with the intention to get rid
of the dependency on the pywin32 package.

But f1fa8f481c7c replaced the usage of the Python standard module _winreg in
lookup_reg as well, which was uneeded (note that lookup_reg was later renamed
into lookupreg).

Basically, we're switching back to the previous _winreg-based implementation,
which uses _winreg.QueryValueEx(). QueryValueEx returns a unicode code string.

See also: issue3467

--- a/mercurial/win32.py	Wed May 30 13:57:41 2012 -0700
+++ b/mercurial/win32.py	Sun May 27 11:29:45 2012 +0200
@@ -5,7 +5,8 @@
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
-import ctypes, errno, os, struct, subprocess, random
+import encoding
+import ctypes, errno, os, subprocess, random, _winreg
 
 _kernel32 = ctypes.windll.kernel32
 _advapi32 = ctypes.windll.advapi32
@@ -69,13 +70,6 @@
 # GetExitCodeProcess
 _STILL_ACTIVE = 259
 
-# registry
-_HKEY_CURRENT_USER = 0x80000001L
-_HKEY_LOCAL_MACHINE = 0x80000002L
-_KEY_READ = 0x20019
-_REG_SZ = 1
-_REG_DWORD = 4
-
 class _STARTUPINFO(ctypes.Structure):
     _fields_ = [('cb', _DWORD),
                 ('lpReserved', _LPSTR),
@@ -179,17 +173,6 @@
 _kernel32.GetConsoleScreenBufferInfo.argtypes = [_HANDLE, ctypes.c_void_p]
 _kernel32.GetConsoleScreenBufferInfo.restype = _BOOL
 
-_advapi32.RegOpenKeyExA.argtypes = [_HANDLE, _LPCSTR, _DWORD, _DWORD,
-    ctypes.c_void_p]
-_advapi32.RegOpenKeyExA.restype = _LONG
-
-_advapi32.RegQueryValueExA.argtypes = [_HANDLE, _LPCSTR, ctypes.c_void_p,
-    ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p]
-_advapi32.RegQueryValueExA.restype = _LONG
-
-_advapi32.RegCloseKey.argtypes = [_HANDLE]
-_advapi32.RegCloseKey.restype = _LONG
-
 _advapi32.GetUserNameA.argtypes = [ctypes.c_void_p, ctypes.c_void_p]
 _advapi32.GetUserNameA.restype = _BOOL
 
@@ -270,33 +253,17 @@
     a sequence of scopes to look up in order. Default (CURRENT_USER,
     LOCAL_MACHINE).
     '''
-    byref = ctypes.byref
     if scope is None:
-        scope = (_HKEY_CURRENT_USER, _HKEY_LOCAL_MACHINE)
+        scope = (_winreg.HKEY_CURRENT_USER, _winreg.HKEY_LOCAL_MACHINE)
     elif not isinstance(scope, (list, tuple)):
         scope = (scope,)
     for s in scope:
-        kh = _HANDLE()
-        res = _advapi32.RegOpenKeyExA(s, key, 0, _KEY_READ, ctypes.byref(kh))
-        if res != _ERROR_SUCCESS:
-            continue
         try:
-            size = _DWORD(600)
-            type = _DWORD()
-            buf = ctypes.create_string_buffer(size.value + 1)
-            res = _advapi32.RegQueryValueExA(kh.value, valname, None,
-                                       byref(type), buf, byref(size))
-            if res != _ERROR_SUCCESS:
-                continue
-            if type.value == _REG_SZ:
-                # string is in ANSI code page, aka local encoding
-                return buf.value
-            elif type.value == _REG_DWORD:
-                fmt = '<L'
-                s = ctypes.string_at(byref(buf), struct.calcsize(fmt))
-                return struct.unpack(fmt, s)[0]
-        finally:
-            _advapi32.RegCloseKey(kh.value)
+            val = _winreg.QueryValueEx(_winreg.OpenKey(s, key), valname)[0]
+            # never let a Unicode string escape into the wild
+            return encoding.tolocal(val.encode('UTF-8'))
+        except EnvironmentError:
+            pass
 
 def executablepath():
     '''return full path of hg.exe'''