Create version tags and GitHub releases based on merges to a main branch

auto-tag-releases.sh

#!/usr/bin/env bash

set -euo pipefail

branch=main
initial_sha=SHA_OF_THE_FIRST_RELEASE
initial_version=1

version_tag () {
  version=$1

  echo "v$version"
}

version_tag_message () {
  previous_version_sha=$1
  version_sha=$2

  git log \
    --oneline \
    --reverse \
    --merges \
    --format='%s' \
    $previous_version_sha..$version_sha \
    | egrep -o 'Merge pull request #[0-9]+' \
    | egrep -o '#[0-9]+' \
    | sed 's/^/- /'
}

add_version_tag () {
  commit_sha=$1
  tag=$2
  message=$3

  commit_date=$(git show --oneline --format='%cD' $commit_sha)

  git tag -d $tag

  set -x
  GIT_COMMITTER_DATE="$commit_date" \
    git tag \
    --annotate \
    --message="$message" \
    $tag $commit_sha
  set +x
}

add_release () {
  tag=$1
  message="$(git tag -l --format='%(contents)' $tag)"

  set -x
  gh release delete -y $tag
  gh release create $tag \
    --title "$tag" \
    --notes "$message"
  set +x
}

deploy_shas () {
  git log \
    $initial_sha..$branch \
    --merges \
    --first-parent $branch \
    --reverse \
    --format='%h'
}

main () {
  initial_tag=$(version_tag $initial_version)
  add_version_tag $initial_sha $initial_tag "Initial production deployment"

  version_tags="$initial_tag"
  previous_sha=$initial_sha
  previous_version=$initial_version

  for deploy_sha in $(deploy_shas); do
    deploy_version=$(expr $previous_version + 1)
    deploy_tag=$(version_tag $deploy_version)
    deploy_message=$(version_tag_message $previous_sha $deploy_sha)

    add_version_tag $deploy_sha $deploy_tag "$deploy_message"

    previous_sha=$deploy_sha
    previous_version=$deploy_version
    version_tags="$version_tags $deploy_tag"
  done

  git push --tags --force

  for version_tag in $version_tags; do
    add_release $version_tag
  done
}

main