Add git-lfs support in RTD environment

Requires tweaking upstream RTD settings to install from pip. This logic
was pulled from a discussion here:

readthedocs/readthedocs.org#1846

Makefile

@@ -132,6 +132,8 @@ update-pip-requirements: ## Updates all Python requirements files via pip-compil
 		securedrop/requirements/test-requirements.in
 	pip-compile --output-file securedrop/requirements/securedrop-app-code-requirements.txt \
 		securedrop/requirements/securedrop-app-code-requirements.in
+	pip-compile --output-file securedrop/requirements/rtd-requirements.txt \
+		securedrop/requirements/rtd-requirements.in
 
 .PHONY: libvirt-share
 libvirt-share: ## Configure ACLs to allow RWX for libvirt VM (e.g. Admin Workstation)

docs/conf.py

@@ -18,6 +18,10 @@
 # https://docs.readthedocs.org/en/latest/faq.html#how-do-i-change-behavior-for-read-the-docs
 on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
 
+# Get SD root directory
+docs_dir = os.path.dirname(os.path.abspath(__file__))
+sd_root_dir = os.path.abspath(os.path.join(docs_dir,'../'))
+
 # 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.
@@ -112,6 +116,10 @@
 # a list of builtin themes.
 if on_rtd:
     html_theme = 'default'
+
+    print('Fetching files with git_lfs')
+    from git_lfs import fetch
+    fetch(sd_root_dir)
 else:
     try:
         # If you want to build the docs locally using the RTD theme,

securedrop/requirements/rtd-requirements.in

@@ -0,0 +1,4 @@
+git-lfs
+sphinx
+sphinx-autobuild
+sphinx_rtd_theme

securedrop/requirements/rtd-requirements.txt

@@ -0,0 +1,36 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --output-file securedrop/requirements/rtd-requirements.txt securedrop/requirements/rtd-requirements.in
+#
+alabaster==0.7.11         # via sphinx
+argh==0.26.2              # via sphinx-autobuild, watchdog
+babel==2.6.0              # via sphinx
+certifi==2018.4.16        # via requests
+chardet==3.0.4            # via requests
+docutils==0.14            # via sphinx
+git-lfs==1.5
+idna==2.7                 # via requests
+imagesize==1.0.0          # via sphinx
+jinja2==2.10              # via sphinx
+livereload==2.5.2         # via sphinx-autobuild
+markupsafe==1.0           # via jinja2
+packaging==17.1           # via sphinx
+pathtools==0.1.2          # via sphinx-autobuild, watchdog
+port-for==0.3.1           # via sphinx-autobuild
+pygments==2.2.0           # via sphinx
+pyparsing==2.2.0          # via packaging
+pytz==2018.4              # via babel
+pyyaml==3.12              # via sphinx-autobuild, watchdog
+requests==2.19.1          # via sphinx
+six==1.11.0               # via livereload, packaging, sphinx
+snowballstemmer==1.2.1    # via sphinx
+sphinx-autobuild==0.7.1
+sphinx-rtd-theme==0.4.0
+sphinx==1.7.5
+sphinxcontrib-websupport==1.1.0  # via sphinx
+tornado==5.0.2            # via livereload, sphinx-autobuild
+typing==3.6.4             # via sphinx
+urllib3==1.23             # via requests
+watchdog==0.8.3           # via sphinx-autobuild