Upload the changes to the generated docs to GitHub artifacts

Building the docs often takes too long locally, so this allows
pull request submitters to build on GitHub, download the changes
and incorporate the changes to the generated docs in a commit,
then update their pull request with the generated docs commit.

Also check that the changes to the prebuilt docs are committed,
except for docs that change for every single rebuild.

.github/workflows/tests.yml

@@ -51,6 +51,29 @@ jobs:
         run: |
           python setup.py build_ext --inplace
           make -C docs/src clean html
+
+      - name: Check changes to prebuilt docs
+        run: |
+          git config user.email "[email protected]"
+          git config user.name "Gensim Docs Build"
+          if ! git diff --quiet @ ; then
+            git add .
+            branch="$GITHUB_HEAD_REF ($GITHUB_REF_NAME)"
+            git commit -m "Import rebuilt documentation for branch $branch"
+            git format-patch @^
+            git bundle create prebuilt-docs-changes.bundle @^...@
+            git reset --mixed @^
+            git diff --exit-code --stat @
+          fi
+
+      - name: Upload prebuilt docs changes
+        if: always()
+        uses: actions/upload-artifact@v3
+        with:
+          name: prebuilt-docs-changes
+          path: |
+            *.patch
+            *.bundle
       #
       # FIXME: do we want to store the built documentation somewhere, or is
       # knowing that the docs built successfully enough?

.gitignore

@@ -75,6 +75,7 @@ data
 *.inv
 *.js
 docs/_images/
+docs/_downloads/
 
 #
 # Generated by Cython