.github: purge workflows on deleted branches

No need to keep workflows on already deleted branches, so purge them.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

.github/scripts/github/gh-purge-deleted-branch-workflows.sh

@@ -0,0 +1,112 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+usage() {
+    echo "Usage: $0 [--dry-run] [--workflow <name>] <owner/repo>"
+    echo
+    echo "Arguments:"
+    echo "  --dry-run          Only show which runs would be deleted (no deletion)"
+    echo "  --workflow <name>  Only purge runs from this workflow name (optional)"
+    echo "  owner/repo         GitHub repository in 'owner/repo' format"
+    exit 1
+}
+
+log_info() { echo "[INFO] $*"; }
+log_warn() { echo "[WARN] $*" >&2; }
+log_error() { echo "[ERROR] $*" >&2; exit 1; }
+
+DRYRUN=false
+WORKFLOW_FILTER=""
+
+# Parse options
+while [[ $# -gt 0 ]]; do
+    case $1 in
+        --dry-run)
+            DRYRUN=true
+            shift
+            ;;
+        --workflow)
+            if [[ $# -lt 2 ]]; then
+                usage
+            fi
+            WORKFLOW_FILTER=$2
+            shift 2
+            ;;
+        *)
+            if [[ -z "${REPO:-}" ]]; then
+                REPO=$1
+                shift
+            else
+                usage
+            fi
+            ;;
+    esac
+done
+
+if [[ -z "${REPO:-}" ]]; then
+    usage
+fi
+
+if ! command -v gh >/dev/null 2>&1; then
+    log_error "GitHub CLI (gh) is required but not installed."
+fi
+if ! command -v jq >/dev/null 2>&1; then
+    log_error "jq is required but not installed."
+fi
+
+# Ensure user is logged in
+if ! gh auth status >/dev/null 2>&1; then
+    log_error "You are not logged in to GitHub CLI. Run: gh auth login"
+fi
+
+# Get all existing branches
+log_info "Fetching existing branches..."
+existing_branches=$(gh api -H "Accept: application/vnd.github+json" \
+    "/repos/${REPO}/branches?per_page=100" --paginate \
+    | jq -r '.[].name' | sort -u)
+
+if [[ -z "$existing_branches" ]]; then
+    log_warn "No branches found in repo. Aborting."
+    exit 0
+fi
+log_info "Found $(echo "$existing_branches" | wc -l) branches."
+
+# Fetch workflow runs
+log_info "Fetching workflow runs..."
+gh api -H "Accept: application/vnd.github+json" \
+    "/repos/${REPO}/actions/runs?per_page=100" --paginate \
+    | jq -c '.workflow_runs[] | {id: .id, branch: .head_branch, workflow: .name}' \
+    | while read -r run; do
+        run_id=$(echo "$run" | jq -r '.id')
+        run_branch=$(echo "$run" | jq -r '.branch')
+        workflow_name=$(echo "$run" | jq -r '.workflow')
+
+        if [[ -z "$run_branch" ]]; then
+            log_warn "Run $run_id has no branch (skipping)."
+            continue
+        fi
+
+        # Skip if branch exists
+        if echo "$existing_branches" | grep -qx "$run_branch"; then
+            continue
+        fi
+
+        # Skip if workflow filter is set and does not match
+        if [[ -n "$WORKFLOW_FILTER" && "$workflow_name" != "$WORKFLOW_FILTER" ]]; then
+            continue
+        fi
+
+        if [[ "$DRYRUN" == true ]]; then
+            log_info "[DRY-RUN] Would delete run $run_id (branch: $run_branch, workflow: $workflow_name)"
+        else
+            log_info "Deleting run $run_id (branch: $run_branch, workflow: $workflow_name)"
+            gh api -X DELETE \
+                "/repos/${REPO}/actions/runs/${run_id}" >/dev/null || true
+        fi
+    done
+
+if [[ "$DRYRUN" == true ]]; then
+    log_info "Dry-run finished. No runs were deleted."
+else
+    log_info "Finished purging workflow runs for deleted branches."
+fi