Make openstackdocstheme an optional doc dependency

cliff is a library that is used outside of OpenStack, too. Having
a build requirement that needs something OpenStack specific makes
life in cases (eg. for downstream packagers) more difficult.
So let's make openstackdocstheme an optional requirement.

Change-Id: I0f94a431be083b8b4baec850b1885ba07b5bf5c2

doc/source/conf.py

@@ -15,7 +15,15 @@
 import datetime
 import subprocess
 
-import openstackdocstheme
+# make openstackdocstheme an optional dependency. cliff is a low level lib
+# that is used outside of OpenStack. Not having something OpenStack specific
+# as build requirement is a good thing.
+try:
+    import openstackdocstheme
+except ImportError:
+    has_openstackdocstheme = False
+else:
+    has_openstackdocstheme = True
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
@@ -32,8 +40,9 @@ import openstackdocstheme
 # ones.
 extensions = [
     'sphinx.ext.autodoc',
-    'openstackdocstheme',
 ]
+if has_openstackdocstheme:
+    extensions.append('openstackdocstheme')
 
 # openstackdocstheme options
 repository_name = 'openstack/cliff'
@@ -109,7 +118,8 @@ pygments_style = 'sphinx'
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 # html_theme = 'default'
-html_theme = 'openstackdocs'
+if has_openstackdocstheme:
+    html_theme = 'openstackdocs'
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
@@ -118,7 +128,8 @@ html_theme = 'openstackdocs'
 
 # Add any paths that contain custom themes here, relative to this directory.
 # html_theme_path = []
-html_theme_path = [openstackdocstheme.get_html_theme_path()]
+if has_openstackdocstheme:
+    html_theme_path = [openstackdocstheme.get_html_theme_path()]
 
 # The name for this set of Sphinx documents.  If None, it defaults to
 # "<project> v<release> documentation".

setup.cfg

@@ -16,6 +16,13 @@ classifier =
     Intended Audience :: Developers
     Environment :: Console
 
+[extras]
+docs =
+    # make openstackdocstheme an optional dependency. cliff is a low level lib
+    # that is used outside of OpenStack. Not having something OpenStack specific
+    # as build requirement is a good thing.
+    openstackdocstheme>=1.16.0 # Apache-2.0
+
 [global]
 setup-hooks =
     pbr.hooks.setup_hook

test-requirements.txt

@@ -12,4 +12,3 @@ coverage!=4.4,>=4.0 # Apache-2.0
 
 # this is required for the docs build jobs
 sphinx>=1.6.2 # BSD
-openstackdocstheme>=1.16.0 # Apache-2.0

tox.ini

@@ -15,6 +15,7 @@ commands =
   python setup.py test --coverage --coverage-package-name=cliff --slowest --testr-args='{posargs}'
   coverage report --show-missing
 deps = -r{toxinidir}/test-requirements.txt
+    .[docs]
 
 [testenv:pep8]
 deps = flake8