#!/bin/sh
#
# Copyright (c) 2006 Johannes E. Schindelin

# SHORT DESCRIPTION
#
# This script makes it easy to fix up commits in the middle of a series,
# and rearrange commits.
#
# The original idea comes from Eric W. Biederman, in
# http://article.gmane.org/gmane.comp.version-control.git/22407

. git-sh-setup

dotest="$GIT_DIR/rebase-merge"

# The file containing rebase commands, comments, and empty lines.
# This file is created by "git rebase -i" then edited by the user.  As
# the lines are processed, they are removed from the front of this
# file and written to the tail of $done.
todo="$dotest"/git-rebase-todo

# The rebase command lines that have already been processed.  A line
# is moved here when it is first handled, before any associated user
# actions.
done="$dotest"/done

# The commit message that is planned to be used for any changes that
# need to be committed following a user interaction.
msg="$dotest"/message

# The file into which is accumulated the suggested commit message for
# squash/fixup commands.  When the first of a series of squash/fixups
# is seen, the file is created and the commit message from the
# previous commit and from the first squash/fixup commit are written
# to it.  The commit message for each subsequent squash/fixup commit
# is appended to the file as it is processed.
#
# The first line of the file is of the form
#     # This is a combination of $count commits.
# where $count is the number of commits whose messages have been
# written to the file so far (including the initial "pick" commit).
# Each time that a commit message is processed, this line is read and
# updated.  It is deleted just before the combined commit is made.
squash_msg="$dotest"/message-squash

# If the current series of squash/fixups has not yet included a squash
# command, then this file exists and holds the commit message of the
# original "pick" commit.  (If the series ends without a "squash"
# command, then this can be used as the commit message of the combined
# commit without opening the editor.)
fixup_msg="$dotest"/message-fixup

# $rewritten is the name of a directory containing files for each
# commit that is reachable by at least one merge base of $head and
# $upstream. They are not necessarily rewritten, but their children
# might be.  This ensures that commits on merged, but otherwise
# unrelated side branches are left alone. (Think "X" in the man page's
# example.)
rewritten="$dotest"/rewritten

dropped="$dotest"/dropped

# A script to set the GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL, and
# GIT_AUTHOR_DATE that will be used for the commit that is currently
# being rebased.
author_script="$dotest"/author-script

# When an "edit" rebase command is being processed, the SHA1 of the
# commit to be edited is recorded in this file.  When "git rebase
# --continue" is executed, if there are any staged changes then they
# will be amended to the HEAD commit, but only provided the HEAD
# commit is still the commit to be edited.  When any other rebase
# command is processed, this file is deleted.
amend="$dotest"/amend

# For the post-rewrite hook, we make a list of rewritten commits and
# their new sha1s.  The rewritten-pending list keeps the sha1s of
# commits that have been processed, but not committed yet,
# e.g. because they are waiting for a 'squash' command.
rewritten_list="$dotest"/rewritten-list
rewritten_pending="$dotest"/rewritten-pending

GIT_CHERRY_PICK_HELP="\
hint: after resolving the conflicts, mark the corrected paths
hint: with 'git add <paths>' and run 'git rebase --continue'"
export GIT_CHERRY_PICK_HELP

warn () {
        printf '%s\n' "$*" >&2
}

output () {
        case "$verbose" in
        '')
                output=$("$@" 2>&1 )
                status=$?
                test $status != 0 && printf "%s\n" "$output"
                return $status
                ;;
        *)
                "$@"
                ;;
        esac
}

# Output the commit message for the specified commit.
commit_message () {
        git cat-file commit "$1" | sed "1,/^$/d"
}

run_pre_rebase_hook () {
        if test -z "$ok_to_skip_pre_rebase" &&
           test -x "$GIT_DIR/hooks/pre-rebase"
        then
                "$GIT_DIR/hooks/pre-rebase" ${1+"$@"} || {
                        echo >&2 "The pre-rebase hook refused to rebase."
                        exit 1
                }
        fi
}


orig_reflog_action="$GIT_REFLOG_ACTION"

comment_for_reflog () {
        case "$orig_reflog_action" in
        ''|rebase*)
                GIT_REFLOG_ACTION="rebase -i ($1)"
                export GIT_REFLOG_ACTION
                ;;
        esac
}

last_count=
mark_action_done () {
        sed -e 1q < "$todo" >> "$done"
        sed -e 1d < "$todo" >> "$todo".new
        mv -f "$todo".new "$todo"
        new_count=$(sane_grep -c '^[^#]' < "$done")
        total=$(($new_count+$(sane_grep -c '^[^#]' < "$todo")))
        if test "$last_count" != "$new_count"
        then
                last_count=$new_count
                printf "Rebasing (%d/%d)\r" $new_count $total
                test -z "$verbose" || echo
        fi
}

make_patch () {
        sha1_and_parents="$(git rev-list --parents -1 "$1")"
        case "$sha1_and_parents" in
        ?*' '?*' '?*)
                git diff --cc $sha1_and_parents
                ;;
        ?*' '?*)
                git diff-tree -p "$1^!"
                ;;
        *)
                echo "Root commit"
                ;;
        esac > "$dotest"/patch
        test -f "$msg" ||
                commit_message "$1" > "$msg"
        test -f "$author_script" ||
                get_author_ident_from_commit "$1" > "$author_script"
}

die_with_patch () {
        echo "$1" > "$dotest"/stopped-sha
        make_patch "$1"
        git rerere
        die "$2"
}

die_abort () {
        rm -rf "$dotest"
        die "$1"
}

has_action () {
        sane_grep '^[^#]' "$1" >/dev/null
}

# Run command with GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL, and
# GIT_AUTHOR_DATE exported from the current environment.
do_with_author () {
        (
                export GIT_AUTHOR_NAME GIT_AUTHOR_EMAIL GIT_AUTHOR_DATE
                "$@"
        )
}

pick_one () {
        ff=--ff
        case "$1" in -n) sha1=$2; ff= ;; *) sha1=$1 ;; esac
        case "$force_rebase" in '') ;; ?*) ff= ;; esac
        output git rev-parse --verify $sha1 || die "Invalid commit name: $sha1"
        test -d "$rewritten" &&
                pick_one_preserving_merges "$@" && return
        if test -n "$rebase_root"
        then
                output git cherry-pick "$@"
                return
        fi
        output git cherry-pick $ff "$@"
}

pick_one_preserving_merges () {
        fast_forward=t
        case "$1" in
        -n)
                fast_forward=f
                sha1=$2
                ;;
        *)
                sha1=$1
                ;;
        esac
        sha1=$(git rev-parse $sha1)

        if test -f "$dotest"/current-commit
        then
                if test "$fast_forward" = t
                then
                        while read current_commit
                        do
                                git rev-parse HEAD > "$rewritten"/$current_commit
                        done <"$dotest"/current-commit
                        rm "$dotest"/current-commit ||
                        die "Cannot write current commit's replacement sha1"
                fi
        fi

        echo $sha1 >> "$dotest"/current-commit

        # rewrite parents; if none were rewritten, we can fast-forward.
        new_parents=
        pend=" $(git rev-list --parents -1 $sha1 | cut -d' ' -s -f2-)"
        if test "$pend" = " "
        then
                pend=" root"
        fi
        while [ "$pend" != "" ]
        do
                p=$(expr "$pend" : ' \([^ ]*\)')
                pend="${pend# $p}"

                if test -f "$rewritten"/$p
                then
                        new_p=$(cat "$rewritten"/$p)

                        # If the todo reordered commits, and our parent is marked for
                        # rewriting, but hasn't been gotten to yet, assume the user meant to
                        # drop it on top of the current HEAD
                        if test -z "$new_p"
                        then
                                new_p=$(git rev-parse HEAD)
                        fi

                        test $p != $new_p && fast_forward=f
                        case "$new_parents" in
                        *$new_p*)
                                ;; # do nothing; that parent is already there
                        *)
                                new_parents="$new_parents $new_p"
                                ;;
                        esac
                else
                        if test -f "$dropped"/$p
                        then
                                fast_forward=f
                                replacement="$(cat "$dropped"/$p)"
                                test -z "$replacement" && replacement=root
                                pend=" $replacement$pend"
                        else
                                new_parents="$new_parents $p"
                        fi
                fi
        done
        case $fast_forward in
        t)
                output warn "Fast-forward to $sha1"
                output git reset --hard $sha1 ||
                        die "Cannot fast-forward to $sha1"
                ;;
        f)
                first_parent=$(expr "$new_parents" : ' \([^ ]*\)')

                if [ "$1" != "-n" ]
                then
                        # detach HEAD to current parent
                        output git checkout $first_parent 2> /dev/null ||
                                die "Cannot move HEAD to $first_parent"
                fi

                case "$new_parents" in
                ' '*' '*)
                        test "a$1" = a-n && die "Refusing to squash a merge: $sha1"

                        # redo merge
                        author_script_content=$(get_author_ident_from_commit $sha1)
                        eval "$author_script_content"
                        msg_content="$(commit_message $sha1)"
                        # No point in merging the first parent, that's HEAD
                        new_parents=${new_parents# $first_parent}
                        if ! do_with_author output \
                                git merge ${strategy:+-s $strategy} -m \
                                        "$msg_content" $new_parents
                        then
                                printf "%s\n" "$msg_content" > "$GIT_DIR"/MERGE_MSG
                                die_with_patch $sha1 "Error redoing merge $sha1"
                        fi
                        echo "$sha1 $(git rev-parse HEAD^0)" >> "$rewritten_list"
                        ;;
                *)
                        output git cherry-pick "$@" ||
                                die_with_patch $sha1 "Could not pick $sha1"
                        ;;
                esac
                ;;
        esac
}

nth_string () {
        case "$1" in
        *1[0-9]|*[04-9]) echo "$1"th;;
        *1) echo "$1"st;;
        *2) echo "$1"nd;;
        *3) echo "$1"rd;;
        esac
}

update_squash_messages () {
        if test -f "$squash_msg"; then
                mv "$squash_msg" "$squash_msg".bak || exit
                count=$(($(sed -n \
                        -e "1s/^# This is a combination of \(.*\) commits\./\1/p" \
                        -e "q" < "$squash_msg".bak)+1))
                {
                        echo "# This is a combination of $count commits."
                        sed -e 1d -e '2,/^./{
                                /^$/d
                        }' <"$squash_msg".bak
                } >"$squash_msg"
        else
                commit_message HEAD > "$fixup_msg" || die "Cannot write $fixup_msg"
                count=2
                {
                        echo "# This is a combination of 2 commits."
                        echo "# The first commit's message is:"
                        echo
                        cat "$fixup_msg"
                } >"$squash_msg"
        fi
        case $1 in
        squash)
                rm -f "$fixup_msg"
                echo
                echo "# This is the $(nth_string $count) commit message:"
                echo
                commit_message $2
                ;;
        fixup)
                echo
                echo "# The $(nth_string $count) commit message will be skipped:"
                echo
                commit_message $2 | sed -e 's/^/#       /'
                ;;
        esac >>"$squash_msg"
}

peek_next_command () {
        sed -n -e "/^#/d" -e '/^$/d' -e "s/ .*//p" -e "q" < "$todo"
}

# A squash/fixup has failed.  Prepare the long version of the squash
# commit message, then die_with_patch.  This code path requires the
# user to edit the combined commit message for all commits that have
# been squashed/fixedup so far.  So also erase the old squash
# messages, effectively causing the combined commit to be used as the
# new basis for any further squash/fixups.  Args: sha1 rest
die_failed_squash() {
        mv "$squash_msg" "$msg" || exit
        rm -f "$fixup_msg"
        cp "$msg" "$GIT_DIR"/MERGE_MSG || exit
        warn
        warn "Could not apply $1... $2"
        die_with_patch $1 ""
}

flush_rewritten_pending() {
        test -s "$rewritten_pending" || return
        newsha1="$(git rev-parse HEAD^0)"
        sed "s/$/ $newsha1/" < "$rewritten_pending" >> "$rewritten_list"
        rm -f "$rewritten_pending"
}

record_in_rewritten() {
        oldsha1="$(git rev-parse $1)"
        echo "$oldsha1" >> "$rewritten_pending"

        case "$(peek_next_command)" in
        squash|s|fixup|f)
                ;;
        *)
                flush_rewritten_pending
                ;;
        esac
}

do_next () {
        rm -f "$msg" "$author_script" "$amend" || exit
        read -r command sha1 rest < "$todo"
        case "$command" in
        '#'*|''|noop)
                mark_action_done
                ;;
        pick|p)
                comment_for_reflog pick

                mark_action_done
                pick_one $sha1 ||
                        die_with_patch $sha1 "Could not apply $sha1... $rest"
                record_in_rewritten $sha1
                ;;
        reword|r)
                comment_for_reflog reword

                mark_action_done
                pick_one $sha1 ||
                        die_with_patch $sha1 "Could not apply $sha1... $rest"
                git commit --amend --no-post-rewrite
                record_in_rewritten $sha1
                ;;
        edit|e)
                comment_for_reflog edit

                mark_action_done
                pick_one $sha1 ||
                        die_with_patch $sha1 "Could not apply $sha1... $rest"
                echo "$sha1" > "$dotest"/stopped-sha
                make_patch $sha1
                git rev-parse --verify HEAD > "$amend"
                warn "Stopped at $sha1... $rest"
                warn "You can amend the commit now, with"
                warn
                warn "  git commit --amend"
                warn
                warn "Once you are satisfied with your changes, run"
                warn
                warn "  git rebase --continue"
                warn
                exit 0
                ;;
        squash|s|fixup|f)
                case "$command" in
                squash|s)
                        squash_style=squash
                        ;;
                fixup|f)
                        squash_style=fixup
                        ;;
                esac
                comment_for_reflog $squash_style

                test -f "$done" && has_action "$done" ||
                        die "Cannot '$squash_style' without a previous commit"

                mark_action_done
                update_squash_messages $squash_style $sha1
                author_script_content=$(get_author_ident_from_commit HEAD)
                echo "$author_script_content" > "$author_script"
                eval "$author_script_content"
                output git reset --soft HEAD^
                pick_one -n $sha1 || die_failed_squash $sha1 "$rest"
                case "$(peek_next_command)" in
                squash|s|fixup|f)
                        # This is an intermediate commit; its message will only be
                        # used in case of trouble.  So use the long version:
                        do_with_author output git commit --no-verify -F "$squash_msg" ||
                                die_failed_squash $sha1 "$rest"
                        ;;
                *)
                        # This is the final command of this squash/fixup group
                        if test -f "$fixup_msg"
                        then
                                do_with_author git commit --no-verify -F "$fixup_msg" ||
                                        die_failed_squash $sha1 "$rest"
                        else
                                cp "$squash_msg" "$GIT_DIR"/SQUASH_MSG || exit
                                rm -f "$GIT_DIR"/MERGE_MSG
                                do_with_author git commit --no-verify -e ||
                                        die_failed_squash $sha1 "$rest"
                        fi
                        rm -f "$squash_msg" "$fixup_msg"
                        ;;
                esac
                record_in_rewritten $sha1
                ;;
        x|"exec")
                read -r command rest < "$todo"
                mark_action_done
                printf 'Executing: %s\n' "$rest"
                # "exec" command doesn't take a sha1 in the todo-list.
                # => can't just use $sha1 here.
                git rev-parse --verify HEAD > "$dotest"/stopped-sha
                ${SHELL:-@SHELL_PATH@} -c "$rest" # Actual execution
                status=$?
                if test "$status" -ne 0
                then
                        warn "Execution failed: $rest"
                        warn "You can fix the problem, and then run"
                        warn
                        warn "  git rebase --continue"
                        warn
                        exit "$status"
                fi
                # Run in subshell because require_clean_work_tree can die.
                if ! (require_clean_work_tree "rebase")
                then
                        warn "Commit or stash your changes, and then run"
                        warn
                        warn "  git rebase --continue"
                        warn
                        exit 1
                fi
                ;;
        *)
                warn "Unknown command: $command $sha1 $rest"
                if git rev-parse --verify -q "$sha1" >/dev/null
                then
                        die_with_patch $sha1 "Please fix this in the file $todo."
                else
                        die "Please fix this in the file $todo."
                fi
                ;;
        esac
        test -s "$todo" && return

        comment_for_reflog finish &&
        headname=$(cat "$dotest"/head-name) &&
        oldhead=$(cat "$dotest"/head) &&
        shortonto=$(git rev-parse --short $(cat "$dotest"/onto)) &&
        newhead=$(git rev-parse HEAD) &&
        case $headname in
        refs/*)
                message="$GIT_REFLOG_ACTION: $headname onto $shortonto" &&
                git update-ref -m "$message" $headname $newhead $oldhead &&
                git symbolic-ref HEAD $headname
                ;;
        esac && {
                test ! -f "$dotest"/verbose ||
                        git diff-tree --stat $(cat "$dotest"/head)..HEAD
        } &&
        {
                test -s "$rewritten_list" &&
                git notes copy --for-rewrite=rebase < "$rewritten_list" ||
                true # we don't care if this copying failed
        } &&
        if test -x "$GIT_DIR"/hooks/post-rewrite &&
                test -s "$rewritten_list"; then
                "$GIT_DIR"/hooks/post-rewrite rebase < "$rewritten_list"
                true # we don't care if this hook failed
        fi &&
        rm -rf "$dotest" &&
        git gc --auto &&
        warn "Successfully rebased and updated $headname."

        exit
}

do_rest () {
        while :
        do
                do_next
        done
}

# skip picking commits whose parents are unchanged
skip_unnecessary_picks () {
        fd=3
        while read -r command rest
        do
                # fd=3 means we skip the command
                case "$fd,$command" in
                3,pick|3,p)
                        # pick a commit whose parent is current $onto -> skip
                        sha1=${rest%% *}
                        case "$(git rev-parse --verify --quiet "$sha1"^)" in
                        "$onto"*)
                                onto=$sha1
                                ;;
                        *)
                                fd=1
                                ;;
                        esac
                        ;;
                3,#*|3,)
                        # copy comments
                        ;;
                *)
                        fd=1
                        ;;
                esac
                printf '%s\n' "$command${rest:+ }$rest" >&$fd
        done <"$todo" >"$todo.new" 3>>"$done" &&
        mv -f "$todo".new "$todo" &&
        case "$(peek_next_command)" in
        squash|s|fixup|f)
                record_in_rewritten "$onto"
                ;;
        esac ||
        die "Could not skip unnecessary pick commands"
}

get_saved_options () {
        test -d "$rewritten" && preserve_merges=t
        test -f "$dotest"/strategy && strategy="$(cat "$dotest"/strategy)"
        test -f "$dotest"/verbose && verbose=t
        test -f "$dotest"/rebase-root && rebase_root=t
}

# Rearrange the todo list that has both "pick sha1 msg" and
# "pick sha1 fixup!/squash! msg" appears in it so that the latter
# comes immediately after the former, and change "pick" to
# "fixup"/"squash".
rearrange_squash () {
        # extract fixup!/squash! lines and resolve any referenced sha1's
        while read -r pick sha1 message
        do
                case "$message" in
                "squash! "*|"fixup! "*)
                        action="${message%%!*}"
                        rest="${message#*! }"
                        echo "$sha1 $action $rest"
                        # if it's a single word, try to resolve to a full sha1 and
                        # emit a second copy. This allows us to match on both message
                        # and on sha1 prefix
                        if test "${rest#* }" = "$rest"; then
                                fullsha="$(git rev-parse -q --verify "$rest" 2>/dev/null)"
                                if test -n "$fullsha"; then
                                        # prefix the action to uniquely identify this line as
                                        # intended for full sha1 match
                                        echo "$sha1 +$action $fullsha"
                                fi
                        fi
                esac
        done >"$1.sq" <"$1"
        test -s "$1.sq" || return

        used=
        while read -r pick sha1 message
        do
                case " $used" in
                *" $sha1 "*) continue ;;
                esac
                printf '%s\n' "$pick $sha1 $message"
                used="$used$sha1 "
                while read -r squash action msg_content
                do
                        case " $used" in
                        *" $squash "*) continue ;;
                        esac
                        emit=0
                        case "$action" in
                        +*)
                                action="${action#+}"
                                # full sha1 prefix test
                                case "$msg_content" in "$sha1"*) emit=1;; esac ;;
                        *)
                                # message prefix test
                                case "$message" in "$msg_content"*) emit=1;; esac ;;
                        esac
                        if test $emit = 1; then
                                printf '%s\n' "$action $squash $action! $msg_content"
                                used="$used$squash "
                        fi
                done <"$1.sq"
        done >"$1.rearranged" <"$1"
        cat "$1.rearranged" >"$1"
        rm -f "$1.sq" "$1.rearranged"
}

LF='
'
parse_onto () {
        case "$1" in
        *...*)
                if      left=${1%...*} right=${1#*...} &&
                        onto=$(git merge-base --all ${left:-HEAD} ${right:-HEAD})
                then
                        case "$onto" in
                        ?*"$LF"?* | '')
                                exit 1 ;;
                        esac
                        echo "$onto"
                        exit 0
                fi
        esac
        git rev-parse --verify "$1^0"
}

case "$action" in
continue)
        get_saved_options
        comment_for_reflog continue

        # Sanity check
        git rev-parse --verify HEAD >/dev/null ||
                die "Cannot read HEAD"
        git update-index --ignore-submodules --refresh &&
                git diff-files --quiet --ignore-submodules ||
                die "Working tree is dirty"

        # do we have anything to commit?
        if git diff-index --cached --quiet --ignore-submodules HEAD --
        then
                : Nothing to commit -- skip this
        else
                . "$author_script" ||
                        die "Cannot find the author identity"
                current_head=
                if test -f "$amend"
                then
                        current_head=$(git rev-parse --verify HEAD)
                        test "$current_head" = $(cat "$amend") ||
                        die "\
You have uncommitted changes in your working tree. Please, commit them
first and then run 'git rebase --continue' again."
                        git reset --soft HEAD^ ||
                        die "Cannot rewind the HEAD"
                fi
                do_with_author git commit --no-verify -F "$msg" -e || {
                        test -n "$current_head" && git reset --soft $current_head
                        die "Could not commit staged changes."
                }
        fi

        record_in_rewritten "$(cat "$dotest"/stopped-sha)"

        require_clean_work_tree "rebase"
        do_rest
        ;;
abort)
        get_saved_options
        comment_for_reflog abort

        git rerere clear

        headname=$(cat "$dotest"/head-name)
        head=$(cat "$dotest"/head)
        case $headname in
        refs/*)
                git symbolic-ref HEAD $headname
                ;;
        esac &&
        output git reset --hard $head &&
        rm -rf "$dotest"
        exit
        ;;
skip)
        get_saved_options
        comment_for_reflog skip

        git rerere clear

        output git reset --hard && do_rest
        ;;
esac

if test -n "$onto"
then
        onto=$(parse_onto "$onto") || die "Does not point to a valid commit: $1"
fi

test -z "$rebase_root" -a $# -ge 1 -a $# -le 2 ||
test ! -z "$rebase_root" -a $# -le 1 || usage

git var GIT_COMMITTER_IDENT >/dev/null ||
        die "You need to set your committer info first"

if test -z "$rebase_root"
then
        upstream_arg="$1"
        upstream=$(git rev-parse --verify "$1") || die "Invalid base"
        test -z "$onto" && onto=$upstream
        shift
else
        upstream=
        upstream_arg=--root
        test -z "$onto" &&
                die "You must specify --onto when using --root"
fi
run_pre_rebase_hook "$upstream_arg" "$@"

comment_for_reflog start

require_clean_work_tree "rebase" "Please commit or stash them."

if test ! -z "$1"
then
        output git checkout "$1" -- ||
                die "Could not checkout $1"
fi

head=$(git rev-parse --verify HEAD) || die "No HEAD?"
mkdir "$dotest" || die "Could not create temporary $dotest"

: > "$dotest"/interactive || die "Could not mark as interactive"
git symbolic-ref HEAD > "$dotest"/head-name 2> /dev/null ||
        echo "detached HEAD" > "$dotest"/head-name

echo $head > "$dotest"/head
case "$rebase_root" in
'')
        rm -f "$dotest"/rebase-root ;;
*)
        : >"$dotest"/rebase-root ;;
esac
echo $onto > "$dotest"/onto
test -z "$strategy" || echo "$strategy" > "$dotest"/strategy
test t = "$verbose" && : > "$dotest"/verbose
if test t = "$preserve_merges"
then
        if test -z "$rebase_root"
        then
                mkdir "$rewritten" &&
                for c in $(git merge-base --all $head $upstream)
                do
                        echo $onto > "$rewritten"/$c ||
                                die "Could not init rewritten commits"
                done
        else
                mkdir "$rewritten" &&
                echo $onto > "$rewritten"/root ||
                        die "Could not init rewritten commits"
        fi
        # No cherry-pick because our first pass is to determine
        # parents to rewrite and skipping dropped commits would
        # prematurely end our probe
        merges_option=
        first_after_upstream="$(git rev-list --reverse --first-parent $upstream..$head | head -n 1)"
else
        merges_option="--no-merges --cherry-pick"
fi

shorthead=$(git rev-parse --short $head)
shortonto=$(git rev-parse --short $onto)
if test -z "$rebase_root"
        # this is now equivalent to ! -z "$upstream"
then
        shortupstream=$(git rev-parse --short $upstream)
        revisions=$upstream...$head
        shortrevisions=$shortupstream..$shorthead
else
        revisions=$onto...$head
        shortrevisions=$shorthead
fi
git rev-list $merges_option --pretty=oneline --abbrev-commit \
        --abbrev=7 --reverse --left-right --topo-order \
        $revisions | \
        sed -n "s/^>//p" |
while read -r shortsha1 rest
do
        if test t != "$preserve_merges"
        then
                printf '%s\n' "pick $shortsha1 $rest" >> "$todo"
        else
                sha1=$(git rev-parse $shortsha1)
                if test -z "$rebase_root"
                then
                        preserve=t
                        for p in $(git rev-list --parents -1 $sha1 | cut -d' ' -s -f2-)
                        do
                                if test -f "$rewritten"/$p -a \( $p != $onto -o $sha1 = $first_after_upstream \)
                                then
                                        preserve=f
                                fi
                        done
                else
                        preserve=f
                fi
                if test f = "$preserve"
                then
                        touch "$rewritten"/$sha1
                        printf '%s\n' "pick $shortsha1 $rest" >> "$todo"
                fi
        fi
done

# Watch for commits that been dropped by --cherry-pick
if test t = "$preserve_merges"
then
        mkdir "$dropped"
        # Save all non-cherry-picked changes
        git rev-list $revisions --left-right --cherry-pick | \
                sed -n "s/^>//p" > "$dotest"/not-cherry-picks
        # Now all commits and note which ones are missing in
        # not-cherry-picks and hence being dropped
        git rev-list $revisions |
        while read rev
        do
                if test -f "$rewritten"/$rev -a "$(sane_grep "$rev" "$dotest"/not-cherry-picks)" = ""
                then
                        # Use -f2 because if rev-list is telling us this commit is
                        # not worthwhile, we don't want to track its multiple heads,
                        # just the history of its first-parent for others that will
                        # be rebasing on top of it
                        git rev-list --parents -1 $rev | cut -d' ' -s -f2 > "$dropped"/$rev
                        short=$(git rev-list -1 --abbrev-commit --abbrev=7 $rev)
                        sane_grep -v "^[a-z][a-z]* $short" <"$todo" > "${todo}2" ; mv "${todo}2" "$todo"
                        rm "$rewritten"/$rev
                fi
        done
fi

test -s "$todo" || echo noop >> "$todo"
test -n "$autosquash" && rearrange_squash "$todo"
cat >> "$todo" << EOF

# Rebase $shortrevisions onto $shortonto
#
# Commands:
#  p, pick = use commit
#  r, reword = use commit, but edit the commit message
#  e, edit = use commit, but stop for amending
#  s, squash = use commit, but meld into previous commit
#  f, fixup = like "squash", but discard this commit's log message
#  x, exec = run command (the rest of the line) using shell
#
# If you remove a line here THAT COMMIT WILL BE LOST.
# However, if you remove everything, the rebase will be aborted.
#
EOF

has_action "$todo" ||
        die_abort "Nothing to do"

cp "$todo" "$todo".backup
git_editor "$todo" ||
        die_abort "Could not execute editor"

has_action "$todo" ||
        die_abort "Nothing to do"

test -d "$rewritten" || test -n "$force_rebase" || skip_unnecessary_picks

output git checkout $onto || die_abort "could not detach HEAD"
git update-ref ORIG_HEAD $head
do_rest