optimize build time (#319)

- Add a GitHub action cache layer
- Refill files modified time to use incremental build
- Change from html builder to dummy builder

Author: Dumeng

.github/scripts/build.sh

@@ -14,4 +14,4 @@ cd cpython/Doc || exit 1
 mkdir -p locales/"$LOCALE"/
 ln -sfn "$(realpath ../../docs)" locales/"$LOCALE"/LC_MESSAGES
 pip3 install -q -r requirements.txt
-make html SPHINXOPTS="-D language=$LOCALE -D gettext_compact=0 -W --keep-going" 2> >(error)
+sphinx-build -b dummy -d build/doctrees  -j auto -D language=$LOCALE -D gettext_compact=0 -W --keep-going -W . build/html 2> >(error)

.github/scripts/update.sh

@@ -1,4 +1,20 @@
 #!/bin/bash
 
+cd cpython || exit 1
+
+# Restore git timestamp for enabling build cache
+rev=HEAD
+for f in $(git ls-tree -r -t --full-name --name-only "$rev" Doc) ; do
+    touch -d $(git log --pretty=format:%cI -1 "$rev" -- "$f") "$f";
+done
+
+cd ..
 cd docs || exit 1
+
+# Restore git timestamp for enabling build cache
+rev=HEAD
+for f in $(git ls-tree -r -t --full-name --name-only "$rev") ; do
+    touch -d $(git log --pretty=format:%cI -1 "$rev" -- "$f") "$f";
+done
+
 $(realpath ../tx) pull --languages "$LOCALE" -t --use-git-timestamps --workers 25 --silent

.github/workflows/sync.yml

@@ -38,8 +38,17 @@ jobs:
         run: .github/scripts/update.sh
         env:
           TX_TOKEN: ${{ secrets.TRANSIFEX_APIKEY }}
+      - uses: actions/cache/restore@v3
+        with:
+          path: cpython/Doc/build
+          key: cache-${{ inputs.version }}-${{ github.run_id }}
+          restore-keys: cache-${{ inputs.version }}-
       - name: build
         run: .github/scripts/build.sh
+      - uses: actions/cache/save@v3
+        with:
+          path: cpython/Doc/build
+          key: cache-${{ inputs.version }}-${{ github.run_id }}
       - name: stat
         run: python .github/scripts/tx_stat.py > ./docs/.stat.json
         env: