Add SemVer compatibility checks (#1556)

This integrates the cargo-semver-checks tool in the CI to check for
SemVer compatibility as per the Cargo reference
(https://doc.rust-lang.org/cargo/reference/semver.html).

The cargo-public-api tool is a viable alternative to
cargo-semver-checks, but I didn't choose it because its comparison
baseline needs to be stored in the repository and manually updated on
each change. For zenoh, the 1.0.0 revision will be the baseline for the
forseeable future.

This comes with a caveat though: cargo-semver-checks accepts a "release
type" argument which would be either patch or minor in zenoh's case. I
specified "patch" since I expect patch releases to be more common. If
the next release is expected to include changes that require a minor
version bump (as defined by the Cargo reference) then the CI workflow
would need to be manually adjusted at the start and the end of the release cycle.

.github/workflows/ci.yml

@@ -25,6 +25,14 @@ env:
   CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
   CARGO_PROFILE_DEV_DEBUG: false
   RUSTUP_WINDOWS_PATH_ADD_BIN: 1
+  # NOTE(fuzzypixelz): This should be changed to "minor" during a release cycle
+  # with plans for changes that REQUIRE a minor version bump as defined by the Cargo reference
+  # (https://doc.rust-lang.org/cargo/reference/semver.html).
+  # However, a minor release could be published without such changes, in which case this variable need not be changed.
+  CARGO_SEMVER_CHECKS_RELEASE_TYPE: patch
+  # NOTE(fuzzypixelz): cargo-semver-checks uses the previous released version as a baseline, not the latest released
+  # version on crates.io. Thus this needs to be updated after every release.
+  CARGO_SEMVER_CHECKS_BASELINE_VERSION: 1.0.0
 
 jobs:
   check:
@@ -51,6 +59,9 @@ jobs:
       - name: Install latest cargo-machete
         uses: taiki-e/install-action@cargo-machete
 
+      - name: Install latest cargo-semver-checks
+        uses: taiki-e/install-action@cargo-semver-checks
+
       - name: Code format check
         run: cargo fmt --check -- --config "unstable_features=true,imports_granularity=Crate,group_imports=StdExternalCrate"
 
@@ -100,6 +111,9 @@ jobs:
       - name: Check unused dependencies
         run: cargo machete
 
+      - name: Check SemVer Compatibility
+        run: cargo +stable semver-checks --verbose --default-features --package zenoh --release-type ${{ env.CARGO_SEMVER_CHECKS_RELEASE_TYPE }} --baseline-version ${{ env.CARGO_SEMVER_CHECKS_BASELINE_VERSION }}
+
   test:
     name: Unit tests on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}