Custom version of `git absorb` which autosquashes unstaged changes

git-fixup-files

#!/usr/bin/env bash
# 
# Try and squash unstaged changes into existing branch commits.
#
# This command examines each unstaged file and attempts to create a fix-up
# commit to squash it into its natural parent in the current branch. 
#
# - If it's able to do this for all modified files, the fix-up files are
#   automatically squashed in.
#
# - If it's unable to do this, fix-up commits are created but not autosquashed
#   and the problematic files have their git history printed to stdout.

set -euo pipefail

main() {
    # Track how many files couldn't be fixed up.
    local num_unfixed_files=0
    local delta

    changed_filepaths | while read -r filepath; 
    do
        delta=$(analyse_filepath "$filepath")
        num_unfixed_files=$((num_unfixed_files + delta))
    done

    if [[ $num_unfixed_files -eq 0 ]]
    then
        # All changes have a fix-up commit - let's autosquash!
        printf "Autosquashing" >&2

        # Specify a no-op editor as we don't want need to be interactive.
        GIT_SEQUENCE_EDITOR=true git rebase -i --autosquash `git merge-base head origin/$(git defaultbranch)`
    fi
}

# Emit a stream of changed filepaths.
changed_filepaths() {
    git status -sb | awk '/^ M/ { print substr($0, 4); }' | sed 's/^"\|"$//g'
}

# Attempt to create a fix-up commit for the passed filepath. Prints 1 if a
# fix-up commit couldn't be created.
analyse_filepath() {
    local filepath="$1"
    local num_unfixed_files=0
    printf "Looking for previous commits for %s - " "$filepath" >&2

    # Count commits on this branch that touch the passed filepath.
    commit_hashes=$(filepath_commit_hashes "$filepath")
    num_commits=$(echo -e "$commit_hashes" | wc -l)
    if [ "$num_commits" -eq 1 ]
    then
        # Only one commit touch the filepath. We assume the unstaged changes
        # can be squashed in so we create a fix-up commit.
        printf "creating fixup commit\n" >&2
        git add "$filepath" >&2
        git commit --no-verify --fixup="$commit_hashes" > /dev/null 2>&1
    else
        # More than one commit touched the filepath. We don't know which of the
        # commits to squash the changes into so we show commits to help decide.
        printf "found %s commits that touched file\n" "$num_commits" >&2
        num_unfixed_files=1
        echo "$commit_hashes" | while read -r sha;
        do
            git show --color --pretty=format:"%h - %s" "$sha" -- "$filepath" >&2
        done
    fi
    
    echo "$num_unfixed_files"
}


# Emit the commit hashes from this branch that touched the passed filepath.
filepath_commit_hashes() {
    git log --format="%H" origin/$(git defaultbranch).. -- "$1"
}

main