chore(ops): add manual caching

Author: strogonoff

.github/workflows/docker.yml

@@ -31,14 +31,57 @@ jobs:
 
       - name: Print Metanorma version
         run: metanorma --version
+      # In case of cache miss, the generate MN XML step will run
+      # and the cache will be filled after job finishes.
+      # Next time it’ll be a cache hit, unless sources changed.
+      # See also “Upload cached Metanorma XML” step, which is important.
+      - name: Restore cached Metanorma XML, if any
+        id: cache-mn-xml
+        uses: actions/cache@v4
+        env:
+          cache-name: _site
+        with:
+          path: _site
+
+          # NOTE: cache key does not include current MN version,
+          # which means if sources did not change but it’s desirable
+          # to rebuild XML using a newer MN version it may be impossible to do
+          # without making a dummy/meaningless change in the content
+          # to change the hash.
+          #
+          # The proper way to address this could be pinning MN version
+          # somewhere and including it as part of the hash here;
+          # alternatively, if we really want to always use whatever MN version
+          # is latest, we could detect that version and include it
+          # as part of this key.
+          key: ${{ runner.os }}-mn-${{ env.cache-name }}-${{ hashFiles('sources/00*-v5/**', 'sources/xmi/**', 'sources/liquid_templates/**', 'sources/guidance/**') }}
+
+          # We can fuzzy-match latest available cache,
+          # instead of precise hash.
+          # This can speed up build in some scenarios,
+          # but can in theory also cause issues where XML is not updated
+          # after source changes.
+          # restore-keys: |
+          #   ${{ runner.os }}-mn-${{ env.cache-name }}-
+          #   ${{ runner.os }}-mn-
+          #   ${{ runner.os }}-
 
       - name: Generate Metanorma XML
         uses: actions-mn/build-and-publish@v2
+        if: steps.cache-mn-xml.outputs.cache-hit != 'true'
         with:
           destination: artifact
           artifact-name: mn
           agree-to-terms: true
-          cache-site-for-manifest: metanorma.yml
+
+      # In case of cache hit, we must explicitly upload the _site dir as artifact
+      - name: Upload cached Metanorma XML
+        uses: actions/upload-artifact@v4
+        if: steps.cache-mn-xml.outputs.cache-hit == 'true'
+        with:
+          name: mn
+          path: _site
+          if-no-files-found: error
 
   fl-build:
     runs-on: ubuntu-latest