git-fixup

#!/bin/bash
# git-fixup (https://github.com/keis/git-fixup)

SUBDIRECTORY_OK=yes
. "$(git --exec-path)/git-sh-setup"

# Define a sed program that turns `git diff` output into a stream of filenames
# and sections within those files.
grok_diff='/^--- .*/p ;
           s/^@@ -\([0-9]*\),\([0-9]*\).*/\1 \2/p'

# Produce suggestion of commits by finding the sections of files with changes
# staged (U1 to diff is used to give some context for when adding items to
# lists etc) and looking up the previous commits touching those sections.
function fixup_candidates_lines () {
    git diff --cached -U1 --no-prefix | sed -n "$grok_diff" | (
        file=''
        while read offs len; do
            if test "$offs" == '---'; then
                file="$len"
            else
                if test "$len" != '0'; then
                    if test "$file" != '/dev/null'; then
                        git blame -sl -L "$offs,+$len" $rev_range -- "$file"
                    fi
                fi
            fi
        done
    ) | grep -v "^^" | cut -d' ' -f 1 | sed 's/^/L /g'
}

# Produce suggestion of commits by taking the latest commit to each file with
# staged changes
function fixup_candidates_files () {
    git diff --cached --name-only | (
        while read file; do
            git rev-list $rev_range -- $file \
                | grep -v -f <(git rev-list -E --grep='^(fixup|squash)' $rev_range -- $file )
        done
    ) | sed 's/^/F /g'
}

# Pretty print details of a commit
function print_sha () {
    local sha=$1
    local type=$2

    git --no-pager log --format="%H [$type] %s <%ae>" -n 1 "$sha"
}

op="fixup"
case "$1" in
    -s|--squash)
        op="squash"
        shift
        ;;
esac

if test $# -eq 1; then
    git commit --$op=$1
    exit
fi

if git diff --cached --quiet; then
    echo 'No staged changes. Use git add -p to add them.' >&2
    exit 1
fi

cd_to_toplevel
upstream=`git rev-parse @{upstream} 2>/dev/null`
head=`git rev-parse HEAD 2>/dev/null`
if test -z "$upstream" -o "$upstream" = "$head"; then
    rev_range="HEAD"
else
    rev_range="@{upstream}..HEAD"
fi

(
    fixup_candidates_lines
    fixup_candidates_files
) | sort -uk2 |  while read type sha; do
    if test "$sha" != ""; then
        print_sha "$sha" "$type"
    fi
done