BUILD-9795 Add support for additional cache fallback branch

Author: mikolaj-matuszny-ext-sonarsource

README.md

@@ -71,6 +71,7 @@ For a feature branch `feature/new-ui`, this will search for:
 | `path`                 | Files, directories, and wildcard patterns to cache | Yes      |         |
 | `key`                  | Explicit key for restoring and saving cache        | Yes      |         |
 | `restore-keys`         | Ordered list of prefix-matched keys for fallback   | No       |         |
+| `fallback-branch`      | Optional branch used for fallback restore keys (must be `main`, `master`, or `branch-*`) | No |         |
 | `environment`          | Environment to use (dev or prod)                   | No       | `prod`  |
 | `upload-chunk-size`    | Chunk size for large file uploads (bytes)          | No       |         |
 | `enableCrossOsArchive` | Enable cross-OS cache compatibility                | No       | `false` |

action.yml

@@ -25,6 +25,8 @@ inputs:
   environment:
     description: Environment to use (dev or prod)
     default: prod
+  fallback-branch:
+    description: Optional branch ref used for fallback restore keys (must be main, master, or branch-*)
 
 outputs:
   cache-hit:
@@ -117,24 +119,36 @@ runs:
             fi
           done <<< "${{ inputs.restore-keys }}"
 
-          # Get the default branch dynamically using GitHub API
-          DEFAULT_BRANCH=$(curl -s -H "Authorization: token ${{ github.token }}" \
-            "https://api.github.com/repos/${{ github.repository }}" | \
-            jq -r '.default_branch')
-
-          # Only allow fallback to supported default branches
-          case "$DEFAULT_BRANCH" in
-            main|master|branch-*)
-              while IFS= read -r line; do
-                if [ -n "$line" ]; then
-                  RESTORE_KEYS="${RESTORE_KEYS}"$'\n'"refs/heads/${DEFAULT_BRANCH}/${line}"
-                fi
-              done <<< "${{ inputs.restore-keys }}"
-              ;;
-            *)
-              echo "::warning::Default branch '$DEFAULT_BRANCH' is not supported for cache fallback. Supported branches: main, master, branch-*"
-              ;;
-          esac
+          # Determine branch to use for fallback restore keys
+          FALLBACK_BRANCH_INPUT="${{ inputs.fallback-branch }}"
+
+          if [[ -n "$FALLBACK_BRANCH_INPUT" ]]; then
+            if [[ "$FALLBACK_BRANCH_INPUT" == refs/heads/* ]]; then
+              FALLBACK_BRANCH_INPUT="${FALLBACK_BRANCH_INPUT#refs/heads/}"
+            fi
+            FALLBACK_BRANCH="$FALLBACK_BRANCH_INPUT"
+          else
+            FALLBACK_BRANCH=$(curl -s -H "Authorization: token ${{ github.token }}" \
+              "https://api.github.com/repos/${{ github.repository }}" | \
+              jq -r '.default_branch')
+          fi
+
+          if [[ -z "$FALLBACK_BRANCH" || "$FALLBACK_BRANCH" == "null" ]]; then
+            echo "::warning::Unable to determine fallback branch; skipping fallback restore keys."
+          else
+            case "$FALLBACK_BRANCH" in
+              main|master|branch-*)
+                while IFS= read -r line; do
+                  if [ -n "$line" ]; then
+                    RESTORE_KEYS="${RESTORE_KEYS}"$'\n'"refs/heads/${FALLBACK_BRANCH}/${line}"
+                  fi
+                done <<< "${{ inputs.restore-keys }}"
+                ;;
+              *)
+                echo "::warning::Fallback branch '$FALLBACK_BRANCH' is not supported for cache fallback. Supported branches: main, master, branch-*"
+                ;;
+            esac
+          fi
 
           echo "branch-restore-keys<<EOF" >> $GITHUB_OUTPUT
           echo "$RESTORE_KEYS" >> $GITHUB_OUTPUT