[PATCH 4 of 6 py3 v4] config: guard against setconfig specifying unicode values on py3

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <raf at durin42.com>
# Date 1488570176 18000
#      Fri Mar 03 14:42:56 2017 -0500
# Node ID eb7a5670afe8cbf8865b890af198608a793ce94c
# Parent  89063bba547df62c98ecee5700c8bd773cb6ef8d
config: guard against setconfig specifying unicode values on py3

This was leading to some difficult to trace problems because the
values were set in one place, but then blew up much later in the
program. Exploding violently with an assertion seems reasonable here.

diff --git a/mercurial/config.py b/mercurial/config.py
--- a/mercurial/config.py
+++ b/mercurial/config.py
@@ -13,6 +13,7 @@ import os
 from .i18n import _
 from . import (
     error,
+    pycompat,
     util,
 )
 
@@ -69,6 +70,9 @@ class config(object):
     def items(self, section):
         return self._data.get(section, {}).items()
     def set(self, section, item, value, source=""):
+        if pycompat.ispy3:
+            assert not isinstance(value, str), (
+                'config values may not be unicode strings on Python 3')
         if section not in self:
             self._data[section] = util.sortdict()
         self._data[section][item] = value