fix: hash extraction for source branches in forks (#3)

Author: lkstrp

action.yml

@@ -59,11 +59,20 @@ runs:
           command_prefix="/home/$USERNAME/runner-scripts/run.sh"
       fi
 
-      # Fetch the hashes (without checking out the code)
+      # Fetch hash of main branch
       _hash_main=$(curl -s -H "Authorization: token $GITHUB_TOKEN" \
       "https://api.github.com/repos/${{ github.repository }}/commits/${{ github.base_ref }}" | jq -r '.sha')
+      
+      # Fetch hash of feature branch (via PR number, also works for branches from forks)
+      pr_details=$(curl -s -H "Authorization: token $GITHUB_TOKEN" \
+          "https://api.github.com/repos/${{ github.repository }}/pulls/${{ github.event.pull_request.number }}")
+      # Extract the repository and ref (branch name)
+      source_repo=$(echo "$pr_details" | jq -r '.head.repo.full_name')
+      branch_name=$(echo "$pr_details" | jq -r '.head.ref')
+      # Get the latest commit hash from the source repository
       _hash_feature=$(curl -s -H "Authorization: token $GITHUB_TOKEN" \
-      "https://api.github.com/repos/${{ github.repository }}/commits/${{ github.head_ref }}" | jq -r '.sha')
+          "https://api.github.com/repos/$source_repo/commits/$branch_name" | jq -r '.sha')
+
       echo "Main branch (${{ github.base_ref }}) hash: $_hash_main"
       echo "Feature branch (${{ github.head_ref }}) hash: $_hash_feature"