ci(forgejo-actions): implement cache of ~/.m2/repository

.gitea/workflows/build.yml

@@ -31,12 +31,48 @@ jobs:
                 }
             }]
 
+      - name: Generate Maven Repository cache keys
+        id: cache-key
+        run: |
+          CURRENT_BRANCH="${{ gitea.base_ref || gitea.ref_name }}"
+          CURRENT_MONTH=$(/bin/date -u "+%Y-%m")
+          CURRENT_DAY=$(/bin/date -u "+%d")
+          ROOT_CACHE_KEY="m2-cache"
+          echo "m2-monthly-cache-key=${ROOT_CACHE_KEY}-${CURRENT_MONTH}" >> $GITEA_OUTPUT
+          echo "m2-monthly-branch-cache-key=${ROOT_CACHE_KEY}-${CURRENT_MONTH}-${CURRENT_BRANCH}" >> $GITEA_OUTPUT
+
+      - name: Cache Maven Repository
+        id: cache-maven
+        uses: https://github.com/actions/cache@v4
+        with:
+          path: ~/.m2/repository
+          # A new cache will be stored daily. After that first store of the day, cache save actions will fail because the cache is immutable but it's not a problem.
+          # The whole cache is dropped monthly to prevent unlimited growth.
+          # The cache is per branch but in case we don't find a branch for a given branch, we will get a cache from another branch.
+          key: ${{ steps.cache-key.outputs.m2-cache-key }}
+          restore-keys: |
+            ${{ steps.cache-key.outputs.m2-monthly-branch-cache-key }}-
+            ${{ steps.cache-key.outputs.m2-monthly-cache-key }}-
+      
+      - name: Restore Maven Repository
+        uses: https://github.com/actions/cache/restore@v4
+        with:
+          path: ~/.m2/repository
+          key: ${{ steps.cache-key.outputs.m2-cache-key }}
+          restore-keys: |
+            ${{ steps.cache-key.outputs.m2-monthly-branch-cache-key }}-
+            ${{ steps.cache-key.outputs.m2-monthly-cache-key }}-
+
       - name: Make maven wrapper executable
         run: chmod +x mvnw
 
+      - name: Populate the cache
+        run: |
+          ./mvnw quarkus:go-offline
+
       - name: Build and run tests
         run: ./mvnw verify
 
-      - name: Upload libs to Gitea Maven Registry
+      - name: Upload libs to Forgejo Maven Registry
         if: gitea.ref == 'refs/heads/main'
         run: ./mvnw deploy -Dmaven.test.skip=true -Dmaven.javadoc.skip=true