Make rust doc deterministic (#878)

Avoid committing if there is no change compared to the previous version,
to keep history clean.

Ref #246

.github/workflows/build_rust_docs.yaml

@@ -52,11 +52,16 @@ jobs:
         run: ./scripts/docker_run ./scripts/build_gh_pages ./out
 
       # From the "out" folder, commit the results and push to gh-pages.
-      # This step only applies to `push` events (not `pull_request`).
+      # This step only applies to `push` events (not `pull_request`), and only if there are actual
+      # changes to commit in the "out" folder.
       - name: Commit and push (post-merge only)
         if: github.event_name == 'push'
         run: |
           cd ./out
           git add .
-          git commit --message="Update gh-pages from ${GITHUB_SHA}"
-          git push
+          if [[ -n "$(git status --porcelain)" ]]; then
+            git commit --message="Update gh-pages from ${GITHUB_SHA}"
+            git push
+          else
+            echo 'no changes to commit'
+          fi

scripts/build_gh_pages

@@ -35,6 +35,9 @@ cargo doc --no-deps --target-dir="${TARGET_DIR}"
 # Remove non-doc artifacts from the target dir.
 rm --recursive --force "${TARGET_DIR}/debug"
 
+# Remove non-deterministic files.
+rm "${TARGET_DIR}/.rustc_info.json"
+
 # The docs generated from the Cargo workspace do not include a workspace-level index, so we generate
 # one here and redirect to the Oak SDK documentation.
 cat <<-END > "${TARGET_DIR}/index.html"