Add extension version check ability with new config value "needs_extensions".

CHANGES

@@ -27,8 +27,9 @@ Features added
 * Added ``sphinx.ext.napoleon`` extension for NumPy and Google style docstring
   support.
 * Added support for extension versions (a string returned by ``setup()``, these
-  can be shown in the traceback log files).  In the future this might also be
-  used for version checking.
+  can be shown in the traceback log files).  Version requirements for extensions
+  can be specified in projects using the new :confval:`needs_extensions` config
+  value.
 * PR#214: Added stemming support for 14 languages, so that the built-in document
   search can now handle these.  Thanks to Shibukawa Yoshiki.
 * PR#202: Allow "." and "~" prefixed references in ``:param:`` doc fields

doc/config.rst

@@ -201,6 +201,19 @@ General configuration
 
    .. versionadded:: 1.0
 
+.. confval:: needs_extensions
+
+   This value can be a dictionary specifying version requirements for extensions
+   in :confval:`extensions`, e.g. ``needs_extensions =
+   {'sphinxcontrib.something': '1.5'}``.  The version strings should be in the
+   form ``major.minor``.  Requirements do not have to be specified for all
+   extensions, only for those you want to check.
+
+   This requires that the extension specifies its version to Sphinx (see
+   :ref:`dev-extensions` for how to do that).
+
+   .. versionadded:: 1.3
+
 .. confval:: nitpicky
 
    If true, Sphinx will warn about *all* references where the target cannot be

sphinx/application.py

@@ -144,6 +144,21 @@ class Sphinx(object):
                 'This project needs at least Sphinx v%s and therefore cannot '
                 'be built with this version.' % self.config.needs_sphinx)
 
+        # check extension versions if requested
+        if self.config.needs_extensions:
+            for extname, needs_ver in self.config.needs_extensions.items():
+                if extname not in self._extensions:
+                    self.warn('needs_extensions config value specifies a '
+                              'version requirement for extension %s, but it is '
+                              'not loaded' % extname)
+                    continue
+                has_ver = self._extension_versions[extname]
+                if has_ver == 'unknown version' or needs_ver > has_ver:
+                    raise VersionRequirementError(
+                        'This project needs the extension %s at least in '
+                        'version %s and therefore cannot be built with the '
+                        'loaded version (%s).' % (extname, needs_ver, has_ver))
+
         # set up translation infrastructure
         self._init_i18n()
         # set up the build environment

sphinx/config.py

@@ -68,6 +68,7 @@ class Config(object):
         trim_doctest_flags = (True, 'env'),
         primary_domain = ('py', 'env'),
         needs_sphinx = (None, None),
+        needs_extensions = ({}, None),
         nitpicky = (False, 'env'),
         nitpick_ignore = ([], 'html'),