add semver ci check

.github/workflows/check.yml

@@ -46,7 +46,23 @@ jobs:
         uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
+  semver:
+    runs-on: ubuntu-latest
+    name: semver
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: true
+      - name: Install stable
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt
+      - name: cargo-semver-checks
+        uses: obi1kenobi/cargo-semver-checks-action@v2
   doc:
+    # run docs generation on nightly rather than stable. This enables features like
+    # https://doc.rust-lang.org/beta/unstable-book/language-features/doc-cfg.html which allows an
+    # API be documented as only available in some specific platforms.
     runs-on: ubuntu-latest
     name: nightly / doc
     steps:
@@ -55,11 +71,13 @@ jobs:
           submodules: true
       - name: Install nightly
         uses: dtolnay/rust-toolchain@nightly
-      - name: cargo doc
-        run: cargo doc --no-deps --all-features
-        env:
-          RUSTDOCFLAGS: --cfg docsrs
+      - name: Install cargo-docs-rs
+        uses: dtolnay/install@cargo-docs-rs
+      - name: cargo docs-rs
+        run: cargo docs-rs
   hack:
+    # cargo-hack checks combinations of feature flags to ensure that features are all additive
+    # which is required for feature unification
     runs-on: ubuntu-latest
     name: ubuntu / stable / features
     steps:
@@ -71,8 +89,9 @@ jobs:
       - name: cargo install cargo-hack
         uses: taiki-e/install-action@cargo-hack
       # intentionally no target specifier; see https://github.com/jonhoo/rust-ci-conf/pull/4
+      # --feature-powerset runs for every combination of features
       - name: cargo hack
-        run: cargo hack --feature-powerset check
+        run: cargo
   msrv:
     runs-on: ubuntu-latest
     # we use a matrix here just because env can't be used in job names