ci: Check for documentation warnings

.github/workflows/ci.yml

@@ -170,3 +170,22 @@ jobs:
       # prost's default features to compile.
       - name: prost-build check
         run: cargo check --manifest-path prost-build/Cargo.toml
+
+  docs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: 'recursive'
+      - name: install protoc
+        uses: taiki-e/install-action@v2
+        with:
+          tool: protoc@${{ env.PROTOC_VERSION }}
+      - name: install ninja
+        uses: ./.github/actions/setup-ninja
+      - uses: dtolnay/rust-toolchain@stable
+      - name: "doc --lib --all-features"
+        run: |
+          cargo doc --lib --no-deps --all-features --document-private-items
+        env:
+          RUSTDOCFLAGS: -Dwarnings

prost-build/src/code_generator/c_escaping.rs

@@ -1,7 +1,7 @@
 use log::debug;
 
 /// Based on [`google::protobuf::UnescapeCEscapeString`][1]
-/// 
+///
 /// [1]: https://github.com/google/protobuf/blob/3.3.x/src/google/protobuf/stubs/strutil.cc#L312-L322
 pub(super) fn unescape_c_escape_string(s: &str) -> Vec<u8> {
     let src = s.as_bytes();