Format staged files on commit, include any formatting changes in the same commit

precommit.sh

#!/bin/sh
####
# The goal of this file is to make sure no code that would fail the style check in CI is committed.
####

# exit early if there are no staged changes
if git diff --cached --quiet; then
  echo "[pre-commit] no staged changes - not doing anything"
  exit 0
fi

# temporarily commit everything that was staged by dev
git commit -m "temp" --no-verify --quiet

STASHED=false
CHANGES=$(git status --porcelain)
# if there were unstaged changes
if [ ! -z "$CHANGES" ]; then
  # stash away everything that was not staged by dev
  git stash --quiet --include-untracked
  STASHED=true
fi

# uncommit the temp commit.
git reset --soft HEAD~

echo "[pre-commit] formatting staged changes"

# format everything
mvn spotless:apply --quiet
# save spotless exit code
RESULT=$?

# stage any additional changes made by spotless
git add --update

if [ "$STASHED" = true ]; then
  # restore everything that was not staged by developer. It will still be unstaged
  git stash pop --quiet
fi

# exit with the code from spotless
exit $RESULT