Checks if the current branch is already contained within the provided target ref.

git-contained.sh

#!/usr/bin/env bash
#
# Checks if the current branch is already contained within the provided target ref.
#
# This solution varies from others with git diff or git log because commits themselves are ignored
# to allow for consistent results if the current branch is rebased/squashed/etc.
# Instead, the change-set as a whole is compared to the target by attempting a merge in a detached
# state and inspecting to see if any resulting merge commit was "empty".
# https://stackoverflow.com/a/55433607/823942

if [[ $# -ne 1 ]]; then
 echo "A single argument is required; the target ref to compare against."
 exit 1
fi

initial_ref=$(git rev-parse --abbrev-ref --verify HEAD)
target_ref="$1"

git checkout --detach --quiet ${target_ref}

if git merge --no-edit --no-ff ${initial_ref} &> /dev/null ; then
  test $(git rev-parse HEAD^{tree}) = $(git rev-parse HEAD^^{tree})
  result=$?
else
  git merge --abort
  result=1
fi

git checkout --force --quiet ${initial_ref}
exit ${result}