git-show-merged-branches

#!/usr/bin/env bash
#
# Copyright (c) 2020 Dan Kalowsky <dank@deadmime.org>.  All rights reserved.
#
# SPDX-License-Identifier: BSD-3-Clause
#

function _display_help {
  echo ""
  echo "==============================================================================="
  echo "Show locally merged branches:                                                  "
  echo -e "\tThis command takes one additional argument to automatically delete the    "
  echo -e "\tmerged branches for you.  By default the command will skip the default    "
  echo -e "\tbranch, release, and the currently selected branches.                     "
  echo "                                                                               "
  echo "Options:                                                                       "
  echo -e "\t-d Adding -d will automatically remove branches discovered to be merged.  "
  echo -e "\t   This will skip the default and release branches.                       "
  echo "==============================================================================="
  echo ""
}

function _old_merge_check() {
  #
  # Now comes the more challenging... building a list of Squash and Merged branches
  # This seems to fail when the branch is rebased on the GitLab and GitHub service
  # and then merged in.
  #
  local merge_base=
  local dangling_commit=

  while read -r branch; do
    if [[ "${merged_local_branches[*]}" =~ ${branch} ]]; then
      #echo "DEBUG: Already found: skipping ${branch}"
      continue
    fi
    merge_base=$(git merge-base "origin/${DEFAULT_BRANCH}" -- "${branch}")

    tree=$(git rev-parse "${branch}"^{tree})
    # okay now create a temporary squash commit
    dangling_commit=$(git commit-tree "${tree}" -p "${merge_base}" -m _)
    # now check if the dangling commit has been squashed to master
    # this works because the next commit should be based upon the predictable history of master
    if [[ $(git cherry "origin/${DEFAULT_BRANCH}" "${dangling_commit}") == "-"* ]]; then
      merged_local_branches=( "${branch}" "${merged_local_branches[@]}" )
      #echo "DEBUG: found squashed branch ${branch}"
    fi
  done < <(git branch --no-color | grep -v -E "(\*|${DEFAULT_BRANCH}*|release*)" | cut -f2 -d $'\t')

}

function _new_merge_check() {
  #
  # This seems to work better for branches that have been rebased on GitLab
  # or GitHub and then merged in.  Not sure if it is completely correct yet.
  #
  while read -r branch; do
    if [[ "${merged_local_branches[*]}" =~ ${branch} ]]; then
      #echo "DEBUG: Already found: skipping ${branch}"
      continue
    fi
    git merge-base --is-ancestor "${branch}" origin/"${DEFAULT_BRANCH}"
    if [ "$?" -eq 0 ]; then
      merged_local_branches=( "${branch}" "${merged_local_branches[@]}" )
    fi
  done < <(git branch --no-color | grep -v -E "(\*|${DEFAULT_BRANCH}*|release*)" | cut -f2 -d $'\t')
}

action="Merged"

#
# It isn't a good practice to just assume the default branch is named master.  Use git to tell
# what is the default branch in use for that specific repo, and use that value instead.
#
DEFAULT_BRANCH=$(git symbolic-ref refs/remotes/origin/HEAD | sed 's@^refs/remotes/origin/@@')

if [ "$#" -eq 1 ]; then
  if [ "$1" == "-h" ]; then
    _display_help
    exit 0
  fi

  if [ "$1" == "-d" ]; then
    action="Deleting"
  fi

  if [ "$1" == "-x" ]; then
    set -o xtrace
    export PS4='+ ${BASH_SOURCE:-}:${FUNCNAME[0]:-}:L${LINENO:-}:   '
  fi
fi

#
# Build the list of traditionally merged branches
#
merged_local_branches=( $(git branch --no-color --merged ${DEFAULT_BRANCH} | grep -v -E "(\*|${DEFAULT_BRANCH}*|release*)" | cut -f2 -d $'\t' ) )

#_old_merge_check
_new_merge_check

#
# Now that we have our list, let's go display it and clean it out if so desired
#
for branch in "${merged_local_branches[@]}"; do
  echo "${action} : ${branch}"
  if [ "${action}" == "Deleting" ]; then
      git branch -D -- "${branch}" &>/dev/null
  fi
done