Print a warning when building docs with a pre-release version of the theme

babel.cfg

@@ -8,3 +8,6 @@
 encoding = utf-8
 ignore_tags = script,style
 include_attrs = alt title summary placeholder
+
+# Extraction from Python files
+[python: **.py]

docs/changelog.rst

@@ -20,6 +20,7 @@ Other Changes
 * Added Spanish translation
 * Added i18n support using Babel
 * Moved build system from Grunt and friends to Webpack
+* Warn when using a pre-release version of the theme
 
 0.4.3
 ======

sphinx_rtd_theme/__init__.py

@@ -5,14 +5,25 @@
 """
 
 from os import path
+import pkg_resources
+
+from sphinx.locale import _
 
 import sphinx
 
+try:
+    # Available from Sphinx 1.6
+    from sphinx.util.logging import getLogger
+except ImportError:
+    from logging import getLogger
+
 
 __version__ = '0.4.3.dev0'
 __version_full__ = __version__
 
 
+logger = getLogger(__name__)
+
 def get_html_theme_path():
     """Return list of HTML theme paths."""
     cur_dir = path.abspath(path.dirname(path.dirname(__file__)))
@@ -23,6 +34,14 @@ def get_html_theme_path():
 def setup(app):
     app.add_html_theme('sphinx_rtd_theme', path.abspath(path.dirname(__file__)))
 
+    # Warn if a prerelease version of the theme is used
+
+    parsed_version = pkg_resources.parse_version(__version__)
+    if parsed_version.is_prerelease:
+        logger.warning(_('You are using a pre-release version (%s) of sphinx-rtd-theme.'), __version__)
+        logger.warning(_('Use a stable release if you encounter problems.'))
+        logger.warning(_('See <https://sphinx-rtd-theme.readthedocs.io/en/stable/installing.html>.'))
+
     if sphinx.version_info >= (1, 8, 0):
         # Add Sphinx message catalog for newer versions of Sphinx
         # See http://www.sphinx-doc.org/en/master/extdev/appapi.html#sphinx.application.Sphinx.add_message_catalog