Make openstackdocstheme an optional doc dependency

stevedore 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: Ic8cc577e617e5da699f9dc43830183005bd2ee66

doc/source/conf.py

@@ -14,6 +14,16 @@
 import datetime
 import subprocess
 
+# make openstackdocstheme an optional dependency. stevedore 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
 # documentation root, use os.path.abspath to make it absolute, like shown here.
@@ -31,9 +41,10 @@ extensions = [
     'sphinx.ext.todo',
     'sphinx.ext.graphviz',
     'sphinx.ext.extlinks',
-    'openstackdocstheme',
     'stevedore.sphinxext',
 ]
+if has_openstackdocstheme:
+    extensions.append('openstackdocstheme')
 
 # openstackdocstheme options
 repository_name = 'openstack/stevedore'
@@ -108,7 +119,8 @@ 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

setup.cfg

@@ -16,6 +16,14 @@ classifier =
     Intended Audience :: Developers
     Environment :: Console
 
+[extras]
+docs =
+    # make openstackdocstheme an optional dependency. stevedore 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

@@ -7,5 +7,4 @@ sphinx>=1.6.2 # BSD
 mock>=2.0.0 # BSD
 coverage!=4.4,>=4.0 # Apache-2.0
 testrepository>=0.0.18 # Apache-2.0/BSD
-openstackdocstheme>=1.16.0 # Apache-2.0
 reno>=2.5.0 # Apache-2.0

tox.ini

@@ -10,6 +10,7 @@ setenv =
 install_command = {toxinidir}/tools/tox_install.sh {env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 deps =
   -r{toxinidir}/test-requirements.txt
+  .[docs]
 distribute = False
 commands = python setup.py testr --testr-args='{posargs}'