CI: Build the docs

Add docs build to the ci script, guard with env var `DO_DOCS` as we do
in other crates in the stack.

Add a docs build job to the CI configuration using the nightly toolchain
as required.

Author: tcharding

.github/workflows/rust.yml

@@ -27,26 +27,26 @@ jobs:
           DO_LINT: true
         run: ./contrib/test.sh
 
-  bench_nightly:
-    name: Bench + Tests
+  Nightly:
+    name: Bench + Docs
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        rust:
-          - nightly
     steps:
       - name: Checkout Crate
         uses: actions/checkout@v2
       - name: Checkout Toolchain
         uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: ${{ matrix.rust }}
+          toolchain: nightly
           override: true
-      - name: Running cargo test
+      - name: Running benchmarks
         env:
           DO_BENCH: true
         run: ./contrib/test.sh
+      - name: Building docs
+        env:
+          DO_DOCS: true
+        run: ./contrib/test.sh
 
   UnitTests:
     name: Tests

contrib/test.sh

@@ -44,12 +44,17 @@ cargo build --examples
 # run all examples
 run-parts ./target/debug/examples
 
-# Bench if told to
+# Bench if told to (this only works with the nightly toolchain)
 if [ "$DO_BENCH" = true ]
 then
     cargo bench --features="unstable compiler"
 fi
 
+# Build the docs if told to (this only works with the nightly toolchain)
+if [ "$DO_DOCS" = true ]; then
+    RUSTDOCFLAGS="--cfg docsrs" cargo doc --all --features="$FEATURES"
+fi
+
 # Run Integration tests if told so
 if [ -n "$BITCOINVERSION" ]; then
     set -e