Ensure the documentation can be built

Signed-off-by: Sean Young <sean@mess.org>

.github/workflows/test.yml

@@ -30,6 +30,22 @@ jobs:
       - name: Run cargo clippy
         run: cargo clippy --workspace --tests --bins -- -D warnings -D clippy::inconsistent-struct-constructor
 
+  docs:
+    name: Docs
+    runs-on: ubuntu-latest
+    container: ubuntu:22.04
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+      - name: Install sphinx
+        run: |
+          export DEBIAN_FRONTEND=noninteractive
+          apt-get update
+          apt-get install -y python3-sphinx python3-sphinx-rtd-theme
+      - name: Build docs
+        run: make html
+        working-directory: docs
+
   linux-x86-64:
     name: Linux x86-64
     runs-on: ubuntu-20.04

docs/Makefile

@@ -3,7 +3,7 @@
 
 # You can set these variables from the command line, and also
 # from the environment for the first two.
-SPHINXOPTS    ?=
+SPHINXOPTS    ?= -W
 SPHINXBUILD   ?= sphinx-build
 SOURCEDIR     = .
 BUILDDIR      = build