feat(ci): check rustdocs on build

Author: jlizen

.github/actions/rust-build/action.yml

@@ -29,3 +29,4 @@ runs:
       if: ${{ inputs.run-tests == 'true' }}
       shell: bash
       run: cargo test --all-features --verbose --package ${{ inputs.package }}
+

.github/workflows/check-docs.yml

@@ -0,0 +1,32 @@
+name: Check rustdocs
+# this is its own workflow since we to to use unstable
+# to have the docs.rs display of feature flags
+
+on:
+  push:
+    paths:
+      - 'lambda*'
+      - 'Cargo.toml'
+
+  pull_request:
+    paths:
+      - 'lambda*'
+      - 'Cargo.toml'
+
+jobs:
+  build-runtime:
+    runs-on: ubuntu-latest
+
+    env:
+      RUST_BACKTRACE: 1
+    steps:
+      - uses: dtolnay/rust-toolchain@master
+        with:
+            toolchain: unstable
+
+      - name: Check documentation
+        shell: bash
+        env:
+            RUSTFLAGS: --cfg docsrs 
+            RUSTDOCFLAGS: --cfg docsrs -Dwarnings
+        run: cargo doc --no-deps --document-private-items --all-features