Add a script to tag and push k0s releases

The script encapsulates the instructions in RELEASE.md and helps to
create and push release tags in the way described.

Signed-off-by: Tom Wieczorek <twieczorek@mirantis.com>

RELEASE.md

@@ -25,6 +25,9 @@ Once the release notes are done we can publish the release.
 
 If for some reason there is an error triggering the action, it is safe to delete the tag remotely with `git push --delete origin <tag>` and push it again.
 
+The above steps are encapsulated in the [`hack/release.sh`](hack/release.sh)
+shell script for convenience.
+
 ## Semver
 
 We're following [semantic versioning](https://semver.org/) for version numbering. Currently we're working on 0.y.z series so the rules are interpreted in bit more relaxed way.

hack/release.sh

@@ -0,0 +1,156 @@
+#!/usr/bin/env sh
+
+set -eu
+
+print_usage() {
+  cat <<EOF
+Usage: $0
+
+Creates and pushes a k0s release tag by performing the following steps:
+
+  - Determine the Kubernetes version
+  - Ask about RC and hotfix numbers
+  - Construct the tag name from the above information
+  - Create the tag and push it to the remote repository
+
+OPTIONS:
+    -h      Show this message
+
+ENVIRONMENT:
+    K0S_SIGNED_TAG   Used to optionally disable tag signing if set to
+                     'no'.
+EOF
+}
+
+confirm_action() {
+  printf '%s (Y/n) ' "$1"
+
+  while :; do
+    read -r yn
+    if [ -n "$yn" ]; then
+      case "$yn" in
+      y | Y) return 0 ;;
+      n | N) return 1 ;;
+      *) printf "To confirm, enter 'y', 'Y' or nothing at all, to decline, enter 'n' or 'N': " ;;
+      esac
+    else
+      return 0
+    fi
+  done
+}
+
+git_get_upstream_remote_for_local_branch() {
+  baseBranchFullRef=$(git rev-parse --symbolic-full-name "$1")
+  upstreamRemoteRef=$(git for-each-ref --format='%(upstream)' "$baseBranchFullRef")
+
+  case "$upstreamRemoteRef" in
+  refs/remotes/*)
+    upstreamRemoteBranch=${upstreamRemoteRef##"refs/remotes/"}
+    echo "${upstreamRemoteBranch%/*}"
+    ;;
+  esac
+}
+
+git_get_current_branch_name() {
+  git rev-parse --symbolic-full-name --abbrev-ref HEAD
+}
+
+determine_k8s_version() {
+  printf %s 'Kubernetes version:  '
+  set -- ./vars.sh kubernetes_version
+  k8sVersion=$("$@" 2>/dev/null) || {
+    retVal=$?
+    echo Failed to determine Kuberntes version! 1>&2
+    "$@"
+    return $retVal
+  }
+
+  echo "$k8sVersion"
+}
+
+determine_git_base_branch() {
+  printf %s 'Base git branch:     '
+  baseBranchName=$(git_get_current_branch_name)
+  echo "$baseBranchName"
+}
+
+determine_upstream_git_remote() {
+  printf %s 'Upstream git remote: '
+  upstreamRemote=$(git_get_upstream_remote_for_local_branch "$baseBranchName")
+  if [ -n "$upstreamRemote" ]; then
+    echo "$upstreamRemote"
+  else
+    echo N/A
+  fi
+}
+
+read_k0s_rc_version() {
+  if confirm_action 'Is the next version a release candidate?'; then
+    while :; do
+      printf %s 'Please enter the release candidate number (e.g. 0, 1, 2, ...): '
+      read -r k0sRc
+      ! [ "$k0sRc" -ge 0 ] 2>/dev/null || return 0
+    done
+  else
+    k0sRc=''
+  fi
+}
+
+read_k0s_hotfix_version() {
+  while :; do
+    printf %s 'Please enter the k0s hotfix number (e.g. 0, 1, 2, ...): '
+    read -r k0sHotfix
+    ! [ "$k0sHotfix" -ge 0 ] 2>/dev/null || return 0
+  done
+}
+
+construct_tag_name() {
+  k0sTag="v$k8sVersion"
+  [ -z "${k0sRc-}" ] || k0sTag="$k0sTag-rc.$k0sRc"
+  k0sTag="$k0sTag+k0s.$k0sHotfix"
+}
+
+create_tag() {
+  set -- git tag -a -m "release $k0sTag"
+  if [ "${K0S_SIGNED_TAG-}" != no ]; then
+    set -- "$@" --sign
+    confirm_action "About to create signed tag '$k0sTag' (disable with K0S_SIGNED_TAG=no). Okay?"
+  else
+    set -- "$@" --no-sign
+    confirm_action "About to create unsigned tag '$k0sTag'. Okay?"
+  fi
+
+  "$@" -- "$k0sTag"
+}
+
+push_tag_to_upstream_remote() {
+  git show "$k0sTag"
+  if [ -n "$upstreamRemote" ]; then
+    if confirm_action "Push the above tag '$k0sTag' to remote '$upstreamRemote'?"; then
+      git push "$upstreamRemote" "$k0sTag"
+    fi
+  fi
+}
+
+do_release() {
+  determine_k8s_version
+  determine_git_base_branch
+  determine_upstream_git_remote
+  read_k0s_rc_version
+  read_k0s_hotfix_version
+  construct_tag_name
+  create_tag
+  push_tag_to_upstream_remote
+}
+
+if [ $# = 1 ] && [ "$1" = h ]; then
+  print_usage
+  exit 1
+fi
+
+if [ $# != 0 ]; then
+  print_usage >&2
+  exit 1
+fi
+
+do_release