Split branch into multiple PRs based on selected files, not commits

split-branch.sh

#!/bin/sh

# TODO:
# - Allow for splitting the same file into multiple branches.
# - If there are manual commits apart from the automatic merges and (split-branch) commits, <do something>. `git merge-base` is useful here.

# Design:
# - The script should be run from the branch that is being split.
# - The script accepts the target branch as an argument.
# - The script will automatically merge the target branch into the source branch if needed.
# - The script will automatically create a pull request for each split branch.

if [ -z "$(command -v git)" ]; then
  echo "You must have git installed to run this script."
  exit 1
fi
if [ -z "$(command -v fzf)" ]; then
  echo "You must have fzf installed to run this script."
  exit 1
fi
if [ -z "$(command -v gh)" ]; then
  echo "You must have gh installed to run this script."
  exit 1
fi
if [ -z "$(command -v jq)" ]; then
  echo "You must have jq installed to run this script."
  exit 1
fi

REPO_ROOT_DIR=$(git rev-parse --show-toplevel)
if [ -z "$REPO_ROOT_DIR" ]; then
  echo "You must be in a git repository to run this script."
  exit 1
fi

TARGET_BRANCH=$1
if [ -z "$TARGET_BRANCH" ]; then
  echo "Usage: $0 <target-branch>"
  exit 1
fi
# Check that the target branch exists.
if [ -z "$(git branch --list $TARGET_BRANCH)" ]; then
  echo "The target branch $TARGET_BRANCH does not exist."
  exit 1
fi
# Source branch is the current branch.
SOURCE_BRANCH=$(git rev-parse --abbrev-ref HEAD)
if [ "$TARGET_BRANCH" == "$SOURCE_BRANCH" ]; then
  echo "You must be on the target branch to run this script."
  exit 1
fi

# Warning if this is the first time the branch is being split.
if [ -z "git branch --list $SOURCE_BRANCH---split---*" ];
then
  read -p "This is the first time $SOURCE_BRANCH is being split. Are you CERTAIN that you want to continue? [Y/n] " answer

  # Default to Yes if the user just presses enter
  answer=${answer:-Y}

  # Check if the response starts with Y or y
  if [[ $answer =~ ^[Yy]$ ]] || [[ -z $answer ]]; then
    echo "Continuing..."
  else
    echo "Exiting."
    exit 1
  fi
fi

if [ "$REPO_ROOT_DIR" != "$PWD" ]; then
  echo "You are in $PWD which is not the root directory $REPO_ROOT_DIR of this git repository."
  read -p "Do you want to change to the root directory before proceeding? [Y/n] " answer

  # Default to Yes if the user just presses enter
  answer=${answer:-Y}

  # Check if the response starts with Y or y
  if [[ $answer =~ ^[Yy]$ ]] || [[ -z $answer ]]; then
    cd "$REPO_ROOT_DIR" || exit
    echo "Changed to the repository root: $REPO_ROOT_DIR"
  else
    echo "Fair. Please change to the root directory manually."
    exit 1
  fi
fi

# Check that the source branch is up to date with the target branch.
if [ $(git merge-base $TARGET_BRANCH $SOURCE_BRANCH) = $(git rev-parse $TARGET_BRANCH) ]; then
  echo "$SOURCE_BRANCH is up-to-date with $TARGET_BRANCH"
else
  read -p "$SOURCE_BRANCH is not up-to-date with $TARGET_BRANCH and a merge is needed. Do you want to merge now? [Y/n] " answer
  answer=${answer:-Y}
  if [[ $answer =~ ^[Yy]$ ]] || [[ -z $answer ]]; then
    git checkout $SOURCE_BRANCH
    RESULT=`git merge $TARGET_BRANCH --no-edit`
    if [ $? -ne 0 ]; then
      echo "$RESULT"
      echo "Failed to automatically merge $TARGET_BRANCH into $SOURCE_BRANCH. Please merge manually. Exiting and leaving the repository in a dirty state."
      exit 1
    fi
    git checkout $TARGET_BRANCH
  else
    echo "Fair. Please merge manually."
    exit 1
  fi
fi

# Create temporary files
split_files_file=$(mktemp)
added_files_file=$(mktemp)
deleted_files_file=$(mktemp)

# Define a cleanup function
EXIT_CODE=1 # Default error code
cleanup() {
  echo "Cleaning up..."
  rm -f "$split_files_file"
  rm -f "$added_files_file"
  rm -f "$deleted_files_file"
  echo "Checking out $SOURCE_BRANCH..."
  git checkout $SOURCE_BRANCH
  exit $EXIT_CODE
}

# Set the trap to call cleanup on script exit, error, or interruption
trap cleanup EXIT INT TERM

# Recalculates the split_files_file. We need to do this after changes to any split branch.
sync_branches_and_recalculate_split_files_file() {
  # Check if split branches already exist for the source branch. Remove leading * if it exists.
  SPLIT_BRANCHES=`git branch --list $SOURCE_BRANCH---split---* | sed 's/^\*[[:space:]]*//'`
  if [ -n "$SPLIT_BRANCHES" ]; then
    # Reset the split_files_file correctly (no empty lines to not confuse grep -v)
    : > "$split_files_file"
    echo "Split branches already exist for $SOURCE_BRANCH."
    echo "$SPLIT_BRANCHES"
    echo "Collecting files that have already been split..."
    for SPLIT_BRANCH in $SPLIT_BRANCHES; do
      # Skip the branch completely if it has a PR that has been merged.
      PR_STATE=`gh pr list --state all --base $TARGET_BRANCH --head $SPLIT_BRANCH --json state | jq -r ".[0].state"`
      # If PR is closed or merged, the branch should be deleted to avoid confusion.
      if [ "$PR_STATE" == "CLOSED" ] || [ "$PR_STATE" == "MERGED" ]; then
        echo "Pull request for split branch $SPLIT_BRANCH has been merged or closed so the branch is ignored."
        echo "If files that were in it have been updated, a new split branch should be created."
      fi

      echo "Checking out $SPLIT_BRANCH..."
      git checkout $SPLIT_BRANCH

      # Extract added files in order to synchronize the split branch with the source branch.
      # We do merging with target branch *after* we synchronize because it should minimize
      # the number of conflicts.
      # TODO: Consider "rebasing" by undoing all the chages (all the additions) and then
      # TODO: merging the target branch and then reapplying the changes.
      git log --pretty=format:"%s" | \
        grep "^(split-branch): +++" | \
        sed 's/^(split-branch): +++ //' | \
        sort | uniq > "$added_files_file"

      # If any of the added files has also been removed and the count is the same, then
      # the file is no longer part of the split branch.
      # If any of the added files that have been split no longer exists in the source branch,
      # remove it from the split branch.
      # If any of the added files that have been split has changed in the source branch,
      # update it in the split branch.
      for FILE in $(cat $added_files_file); do
        # Count additions of the specific file
        count_additions=$(git log --pretty=format:"%s" | grep -c "^(split-branch): +++ $FILE")
        # Count deletions of the specific file
        count_deletions=$(git log --pretty=format:"%s" | grep -c "^(split-branch): --- $FILE")
        net_additions=$((count_additions - count_deletions))
        if [ "$net_additions" -eq 1 ]; then
          # The file belongs to the split branch.
          echo "$FILE" >> "$split_files_file"
        elif [ "$net_additions" -eq 0 ]; then
          # The file no longer belongs to the split branch.
          continue
        else
          echo "Error: Inconsistent file history for $FILE, net additions $net_additions. Aborting."
          EXIT_CODE=100
          exit $EXIT_CODE
        fi

        # Skip synchronization if the branch has been marked to be in the manual mode.
        # TODO: Count the +manual/-manual.
        if [ -n "$(git log --pretty=format:"%s" | grep "^(split-branch): +manual")" ]; then
          echo "Split branch $SPLIT_BRANCH has been marked as in manual mode. Skipping synchronization..."
          continue
        fi

        # Synchronize the file with the source branch.
        if [ -z "$(git ls-tree -r --name-only "$SOURCE_BRANCH" | grep "^$FILE$")" ]; then
          echo "File $FILE has been deleted in source branch. Removing from $SPLIT_BRANCH..."
          git rm $FILE
          git commit -m "(split-branch): --- $FILE"
        else
          if git diff --quiet "$SOURCE_BRANCH" "$SPLIT_BRANCH" -- "$FILE"; then
            echo "File $FILE has not changed in source branch. Skipping..."
          else
            echo "File $FILE has changed in source branch. Updating in $SPLIT_BRANCH..."
            git checkout "$SOURCE_BRANCH" -- "$FILE"
            git add "$FILE"
            # Mark this operation with === as it's not adding a new file, just updating an existing one.
            git commit -m "(split-branch): === $FILE"
          fi
        fi
      done

      # After syncing, automatically merge the target branch into the split branch if needed.
      # The user already gave us permission to merge the source branch into the target branch so we don't ask again.
      if [ $(git merge-base "$TARGET_BRANCH" "$SPLIT_BRANCH") = $(git rev-parse "$TARGET_BRANCH") ]; then
        echo "$SPLIT_BRANCH is up-to-date with $TARGET_BRANCH"
      else
        echo "$SPLIT_BRANCH is not up-to-date with $TARGET_BRANCH and a merge is needed. Merging now..."
        RESULT=`git merge $TARGET_BRANCH --no-edit`
        if [ $? -ne 0 ]; then
          echo "$RESULT"
          echo "Failed to automatically merge $TARGET_BRANCH into $SPLIT_BRANCH. Please merge manually. Exiting and leaving the repository in a dirty state."
          exit 1
        fi
      fi
    done

    echo "The following files have already been split:"
    cat "$split_files_file"
  fi
}

echo "Splitting $SOURCE_BRANCH from $TARGET_BRANCH..."

# Main interactive loop:
# - Collect all the files that have already been split into different branches.
# - Check the difference between the $TARGET_BRANCH and $SOURCE_BRANCH.
# - Distribute the files that have not been split yet into different branches or remove the files
# from the split branches if so desired.
while [ 1 ]; do
  RESULT=`sync_branches_and_recalculate_split_files_file`
  if [ $? -ne 0 ]; then
    echo "$RESULT"
    echo "Failed to synchronize branches. Exiting and leaving the repository in a dirty state."
    EXIT_CODE=3
    exit $EXIT_CODE
  fi

  git checkout $TARGET_BRANCH
  DIFF_FILES=`git diff --name-only $SOURCE_BRANCH $TARGET_BRANCH | grep -v -f "$split_files_file"`
  echo "changed files: $(git diff --name-only $SOURCE_BRANCH $TARGET_BRANCH)"
  echo "diff files: $DIFF_FILES"
  read -p "Do you want to make any changes to the split branches? [N/y] " answer
  answer=${answer:-N}
  if [[ $answer =~ ^[Nn]$ ]]; then
    break
  fi

  # Get the suffix for the split branch.
  EXIT_CODE=2

  # Get the split branches and allow the user to choose which one to add to.
  SPLIT_BRANCH=$(echo "<new branch>\n$(git branch --list "$SOURCE_BRANCH---split---*" | sed 's/^\*[[:space:]]*//')" | fzf --cycle --header-first --header "Choose the split branch to add to or a new branch option." --preview "git diff --color=always $TARGET_BRANCH {}")
  echo $SPLIT_BRANCH
  if [[ -z "$SPLIT_BRANCH" ]] || [[ "$SPLIT_BRANCH" == "<new branch>" ]]; then
    read -p "Enter the suffix for the new branch: [cancel] " SPLIT_SUFFIX
    if [ -z "$SPLIT_SUFFIX" ]; then
      # Go back to the beginning of the loop.
      continue
    fi
  else
    read -p "Do you want to add new files or remove files from this branch? [y/N] " answer
    answer=${answer:-N}
    if [[ $answer =~ ^[Nn]$ ]]; then
      continue
    fi
    SPLIT_SUFFIX=`echo $SPLIT_BRANCH | sed 's/.*---//'`
  fi

  FILES_TO_ADD=`echo "$DIFF_FILES" | fzf -m --cycle --header-first --header "Choose files to add to branch $SPLIT_SUFFIX. Esc if nothing to select." --preview "git diff --color=always $TARGET_BRANCH $SOURCE_BRANCH -- {}"`
  FILES_TO_REMOVE=`echo "$SPLIT_FILES" | fzf -m --cycle --header-first --header "Choose files to remove from $SPLIT_SUFFIX. Esc if nothing to select." --preview "git diff --color=always $TARGET_BRANCH $SOURCE_BRANCH -- {}"`

  if [ -z "$FILES_TO_ADD" ] && [ -z "$FILES_TO_REMOVE" ]; then
    echo "No files were selected to either be added or removed. Repeating the process."
    continue
  fi

  # Checkout the branch and add/remove the files.
  if [ -n "$(git branch --list $SOURCE_BRANCH---split---$SPLIT_SUFFIX)" ]; then
    git checkout $SOURCE_BRANCH---split---$SPLIT_SUFFIX
  else
    git checkout -b $SOURCE_BRANCH---split---$SPLIT_SUFFIX
  fi
  # Add the files to the split branch from the source branch.
  for FILE in $FILES_TO_ADD; do
    git checkout $SOURCE_BRANCH -- "$FILE"
    git add "$FILE"
    git commit -m "(split-branch): +++ $FILE"
  done
  # Remove the files from the split branch by checking them out from the target branch or deleting them (if they are new files)
  for FILE in $FILES_TO_REMOVE; do
    if [ -n "$(git ls-tree -r --name-only "$TARGET_BRANCH" | grep "^$FILE$")" ]; then
      git checkout $TARGET_BRANCH -- "$FILE"
    else
      git rm "$FILE"
    fi
    git commit -m "(split-branch): --- $FILE"
  done
done;

# Now go over each branch and push it to the remote repository.
for SPLIT_BRANCH in `git branch --list $SOURCE_BRANCH---split---* | sed 's/^\*[[:space:]]*//'`; do
  echo "Pushing $SPLIT_BRANCH..."
  git checkout $SPLIT_BRANCH
  git push --no-verify --set-upstream origin $SPLIT_BRANCH

  # Check if the pull request already exists for this branch.
  PR=`gh pr list --state all --base $TARGET_BRANCH --head $SPLIT_BRANCH --json url | jq -r ".[0].url"`
  if [[ -n "$PR" ]] && [[ "$PR" != "null" ]]; then
    echo "Pull request already exists for $SPLIT_BRANCH into $TARGET_BRANCH: $PR"
    continue
  fi

  # Ask the user if they want to create a pull request assuming GitHub.
  read -p "Do you want to create a pull request for $SPLIT_BRANCH? [Y/n] " answer

  # Default to Yes if the user just presses enter
  answer=${answer:-Y}

  # Check if the response starts with Y or y
  if [[ $answer =~ ^[Yy]$ ]] || [[ -z $answer ]]; then
    # Create a pull request with suffix being all the characters after the last `---` in the branch name.
    SUFFIX=`echo $SPLIT_BRANCH | sed 's/.*---//'`
    gh pr create -B $TARGET_BRANCH -H $SPLIT_BRANCH -t "Split $SOURCE_BRANCH for $SUFFIX"
    PR=`gh pr list --state all --base $TARGET_BRANCH --head $SPLIT_BRANCH --json url | jq -r ".[0].url"`
    echo "Pull request created for $SPLIT_BRANCH into $TARGET_BRANCH: $PR"
  fi
done

# Signal that we are exiting cleanly.
EXIT_CODE=0

Ok now the main interactive loop works with files rather than a set of branches (branches are still there of course, but secondary to files)