Show traceback if conf.py raises an exception (refs: #4369)

CHANGES

@@ -17,6 +17,7 @@ Features added
 * ``VerbatimHighlightColor`` is a new
   :ref:`LaTeX 'sphinxsetup' <latexsphinxsetup>` key (refs: #4285)
 * Easier customizability of LaTeX macros involved in rendering of code-blocks
+* Show traceback if conf.py raises an exception (refs: #4369)
 
 Bugs fixed
 ----------

sphinx/config.py

@@ -10,6 +10,7 @@
 """
 
 import re
+import traceback
 from os import path, getenv
 
 from six import PY2, PY3, iteritems, string_types, binary_type, text_type, integer_types
@@ -35,6 +36,7 @@ copyright_year_re = re.compile(r'^((\d{4}-)?)(\d{4})(?=[ ,])')
 CONFIG_SYNTAX_ERROR = "There is a syntax error in your configuration file: %s"
 if PY3:
     CONFIG_SYNTAX_ERROR += "\nDid you change the syntax from 2.x to 3.x?"
+CONFIG_ERROR = "There is a programable error in your configuration file:\n\n%s"
 CONFIG_EXIT_ERROR = "The configuration file (or one of the modules it imports) " \
                     "called sys.exit()"
 CONFIG_ENUM_WARNING = "The config value `{name}` has to be a one of {candidates}, " \
@@ -152,6 +154,8 @@ class Config(object):
                     raise ConfigError(CONFIG_SYNTAX_ERROR % err)
                 except SystemExit:
                     raise ConfigError(CONFIG_EXIT_ERROR)
+                except Exception:
+                    raise ConfigError(CONFIG_ERROR % traceback.format_exc())
 
         self._raw_config = config
         # these two must be preinitialized because extensions can add their