[GSoC] [PATCH 0/5] rebase: rewrite rebase in C

@@ -0,0 +1,738 @@
+#!/bin/sh
+#
+# Copyright (c) 2005 Junio C Hamano.
+#
+
+SUBDIRECTORY_OK=Yes
+OPTIONS_KEEPDASHDASH=
+OPTIONS_STUCKLONG=t
+OPTIONS_SPEC="\
+git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] [<upstream>] [<branch>]
+git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] --root [<branch>]
+git rebase --continue | --abort | --skip | --edit-todo
+--
+ Available options are
+v,verbose!         display a diffstat of what changed upstream
+q,quiet!           be quiet. implies --no-stat
+autostash          automatically stash/stash pop before and after
+fork-point         use 'merge-base --fork-point' to refine upstream
+onto=!             rebase onto given branch instead of upstream
+r,rebase-merges?   try to rebase merges instead of skipping them
+p,preserve-merges! try to recreate merges instead of ignoring them
+s,strategy=!       use the given merge strategy
+no-ff!             cherry-pick all commits, even if unchanged
+m,merge!           use merging strategies to rebase
+i,interactive!     let the user edit the list of commits to rebase
+x,exec=!           add exec lines after each commit of the editable list
+k,keep-empty	   preserve empty commits during rebase
+allow-empty-message allow rebasing commits with empty messages
+f,force-rebase!    force rebase even if branch is up to date
+X,strategy-option=! pass the argument through to the merge strategy
+stat!              display a diffstat of what changed upstream
+n,no-stat!         do not show diffstat of what changed upstream
+verify             allow pre-rebase hook to run
+rerere-autoupdate  allow rerere to update index with resolved conflicts
+root!              rebase all reachable commits up to the root(s)
+autosquash         move commits that begin with squash!/fixup! under -i
+committer-date-is-author-date! passed to 'git am'
+ignore-date!       passed to 'git am'
+signoff            passed to 'git am'
+whitespace=!       passed to 'git apply'
+ignore-whitespace! passed to 'git apply'
+C=!                passed to 'git apply'
+S,gpg-sign?        GPG-sign commits
+ Actions:
+continue!          continue
+abort!             abort and check out the original branch
+skip!              skip current patch and continue
+edit-todo!         edit the todo list during an interactive rebase
+quit!              abort but keep HEAD where it is
+show-current-patch! show the patch file being applied or merged
+"
+. git-sh-setup
+set_reflog_action rebase
+require_work_tree_exists
+cd_to_toplevel
+
+LF='
+'
+ok_to_skip_pre_rebase=
+resolvemsg="
+$(gettext 'Resolve all conflicts manually, mark them as resolved with
+"git add/rm <conflicted_files>", then run "git rebase --continue".
+You can instead skip this commit: run "git rebase --skip".
+To abort and get back to the state before "git rebase", run "git rebase --abort".')
+"
+squash_onto=
+unset onto
+unset restrict_revision
+cmd=
+strategy=
+strategy_opts=
+do_merge=
+merge_dir="$GIT_DIR"/rebase-merge
+apply_dir="$GIT_DIR"/rebase-apply
+verbose=
+diffstat=
+test "$(git config --bool rebase.stat)" = true && diffstat=t
+autostash="$(git config --bool rebase.autostash || echo false)"
+fork_point=auto
+git_am_opt=
+git_format_patch_opt=
+rebase_root=
+force_rebase=
+allow_rerere_autoupdate=
+# Non-empty if a rebase was in progress when 'git rebase' was invoked
+in_progress=
+# One of {am, merge, interactive}
+type=
+# One of {"$GIT_DIR"/rebase-apply, "$GIT_DIR"/rebase-merge}
+state_dir=
+# One of {'', continue, skip, abort}, as parsed from command line
+action=
+rebase_merges=
+rebase_cousins=
+preserve_merges=
+autosquash=
+keep_empty=
+allow_empty_message=
+signoff=
+test "$(git config --bool rebase.autosquash)" = "true" && autosquash=t
+case "$(git config --bool commit.gpgsign)" in
+true)	gpg_sign_opt=-S ;;
+*)	gpg_sign_opt= ;;
+esac
+
+read_basic_state () {
+	test -f "$state_dir/head-name" &&
+	test -f "$state_dir/onto" &&
+	head_name=$(cat "$state_dir"/head-name) &&
+	onto=$(cat "$state_dir"/onto) &&
+	# We always write to orig-head, but interactive rebase used to write to
+	# head. Fall back to reading from head to cover for the case that the
+	# user upgraded git with an ongoing interactive rebase.
+	if test -f "$state_dir"/orig-head
+	then
+		orig_head=$(cat "$state_dir"/orig-head)
+	else
+		orig_head=$(cat "$state_dir"/head)
+	fi &&
+	GIT_QUIET=$(cat "$state_dir"/quiet) &&
+	test -f "$state_dir"/verbose && verbose=t
+	test -f "$state_dir"/strategy && strategy="$(cat "$state_dir"/strategy)"
+	test -f "$state_dir"/strategy_opts &&
+		strategy_opts="$(cat "$state_dir"/strategy_opts)"
+	test -f "$state_dir"/allow_rerere_autoupdate &&
+		allow_rerere_autoupdate="$(cat "$state_dir"/allow_rerere_autoupdate)"
+	test -f "$state_dir"/gpg_sign_opt &&
+		gpg_sign_opt="$(cat "$state_dir"/gpg_sign_opt)"
+	test -f "$state_dir"/signoff && {
+		signoff="$(cat "$state_dir"/signoff)"
+		force_rebase=t
+	}
+}
+
+write_basic_state () {
+	echo "$head_name" > "$state_dir"/head-name &&
+	echo "$onto" > "$state_dir"/onto &&
+	echo "$orig_head" > "$state_dir"/orig-head &&
+	echo "$GIT_QUIET" > "$state_dir"/quiet &&
+	test t = "$verbose" && : > "$state_dir"/verbose
+	test -n "$strategy" && echo "$strategy" > "$state_dir"/strategy
+	test -n "$strategy_opts" && echo "$strategy_opts" > \
+		"$state_dir"/strategy_opts
+	test -n "$allow_rerere_autoupdate" && echo "$allow_rerere_autoupdate" > \
+		"$state_dir"/allow_rerere_autoupdate
+	test -n "$gpg_sign_opt" && echo "$gpg_sign_opt" > "$state_dir"/gpg_sign_opt
+	test -n "$signoff" && echo "$signoff" >"$state_dir"/signoff
+}
+
+output () {
+	case "$verbose" in
+	'')
+		output=$("$@" 2>&1 )
+		status=$?
+		test $status != 0 && printf "%s\n" "$output"
+		return $status
+		;;
+	*)
+		"$@"
+		;;
+	esac
+}
+
+move_to_original_branch () {
+	case "$head_name" in
+	refs/*)
+		message="rebase finished: $head_name onto $onto"
+		git update-ref -m "$message" \
+			$head_name $(git rev-parse HEAD) $orig_head &&
+		git symbolic-ref \
+			-m "rebase finished: returning to $head_name" \
+			HEAD $head_name ||
+		die "$(eval_gettext "Could not move back to \$head_name")"
+		;;
+	esac
+}
+
+apply_autostash () {
+	if test -f "$state_dir/autostash"
+	then
+		stash_sha1=$(cat "$state_dir/autostash")
+		if git stash apply $stash_sha1 >/dev/null 2>&1
+		then
+			echo "$(gettext 'Applied autostash.')" >&2
+		else
+			git stash store -m "autostash" -q $stash_sha1 ||
+			die "$(eval_gettext "Cannot store \$stash_sha1")"
+			gettext 'Applying autostash resulted in conflicts.
+Your changes are safe in the stash.
+You can run "git stash pop" or "git stash drop" at any time.
+' >&2
+		fi
+	fi
+}
+
+finish_rebase () {
+	rm -f "$(git rev-parse --git-path REBASE_HEAD)"
+	apply_autostash &&
+	{ git gc --auto || true; } &&
+	rm -rf "$state_dir"
+}
+
+run_specific_rebase () {
+	if [ "$interactive_rebase" = implied ]; then
+		GIT_EDITOR=:
+		export GIT_EDITOR
+		autosquash=
+	fi
+	. git-rebase--$type
+
+	if test -z "$preserve_merges"
+	then
+		git_rebase__$type
+	else
+		git_rebase__preserve_merges
+	fi
+
+	ret=$?
+	if test $ret -eq 0
+	then
+		finish_rebase
+	elif test $ret -eq 2 # special exit status for rebase -i
+	then
+		apply_autostash &&
+		rm -rf "$state_dir" &&
+		die "Nothing to do"
+	fi
+	exit $ret
+}
+
+run_pre_rebase_hook () {
+	if test -z "$ok_to_skip_pre_rebase" &&
+	   test -x "$(git rev-parse --git-path hooks/pre-rebase)"
+	then
+		"$(git rev-parse --git-path hooks/pre-rebase)" ${1+"$@"} ||
+		die "$(gettext "The pre-rebase hook refused to rebase.")"
+	fi
+}
+
+test -f "$apply_dir"/applying &&
+	die "$(gettext "It looks like 'git am' is in progress. Cannot rebase.")"
+
+if test -d "$apply_dir"
+then
+	type=am
+	state_dir="$apply_dir"
+elif test -d "$merge_dir"
+then
+	if test -d "$merge_dir"/rewritten
+	then
+		type=preserve-merges
+		interactive_rebase=explicit
+		preserve_merges=t
+	elif test -f "$merge_dir"/interactive
+	then
+		type=interactive
+		interactive_rebase=explicit
+	else
+		type=merge
+	fi
+	state_dir="$merge_dir"
+fi
+test -n "$type" && in_progress=t
+
+total_argc=$#
+while test $# != 0
+do
+	case "$1" in
+	--no-verify)
+		ok_to_skip_pre_rebase=yes
+		;;
+	--verify)
+		ok_to_skip_pre_rebase=
+		;;
+	--continue|--skip|--abort|--quit|--edit-todo|--show-current-patch)
+		test $total_argc -eq 2 || usage
+		action=${1##--}
+		;;
+	--onto=*)
+		onto="${1#--onto=}"
+		;;
+	--exec=*)
+		cmd="${cmd}exec ${1#--exec=}${LF}"
+		test -z "$interactive_rebase" && interactive_rebase=implied
+		;;
+	--interactive)
+		interactive_rebase=explicit
+		;;
+	--keep-empty)
+		keep_empty=yes
+		;;
+	--allow-empty-message)
+		allow_empty_message=--allow-empty-message
+		;;
+	--no-keep-empty)
+		keep_empty=
+		;;
+	--rebase-merges)
+		rebase_merges=t
+		test -z "$interactive_rebase" && interactive_rebase=implied
+		;;
+	--rebase-merges=*)
+		rebase_merges=t
+		case "${1#*=}" in
+		rebase-cousins) rebase_cousins=t;;
+		no-rebase-cousins) rebase_cousins=;;
+		*) die "Unknown mode: $1";;
+		esac
+		test -z "$interactive_rebase" && interactive_rebase=implied
+		;;
+	--preserve-merges)
+		preserve_merges=t
+		test -z "$interactive_rebase" && interactive_rebase=implied
+		;;
+	--autosquash)
+		autosquash=t
+		;;
+	--no-autosquash)
+		autosquash=
+		;;
+	--fork-point)
+		fork_point=t
+		;;
+	--no-fork-point)
+		fork_point=
+		;;
+	--merge)
+		do_merge=t
+		;;
+	--strategy-option=*)
+		strategy_opts="$strategy_opts $(git rev-parse --sq-quote "--${1#--strategy-option=}")"
+		do_merge=t
+		test -z "$strategy" && strategy=recursive
+		;;
+	--strategy=*)
+		strategy="${1#--strategy=}"
+		do_merge=t
+		;;
+	--no-stat)
+		diffstat=
+		;;
+	--stat)
+		diffstat=t
+		;;
+	--autostash)
+		autostash=true
+		;;
+	--no-autostash)
+		autostash=false
+		;;
+	--verbose)
+		verbose=t
+		diffstat=t
+		GIT_QUIET=
+		;;
+	--quiet)
+		GIT_QUIET=t
+		git_am_opt="$git_am_opt -q"
+		verbose=
+		diffstat=
+		;;
+	--whitespace=*)
+		git_am_opt="$git_am_opt --whitespace=${1#--whitespace=}"
+		case "${1#--whitespace=}" in
+		fix|strip)
+			force_rebase=t
+			;;
+		esac
+		;;
+	--ignore-whitespace)
+		git_am_opt="$git_am_opt $1"
+		;;
+	--signoff)
+		signoff=--signoff
+		;;
+	--no-signoff)
+		signoff=
+		;;
+	--committer-date-is-author-date|--ignore-date)
+		git_am_opt="$git_am_opt $1"
+		force_rebase=t
+		;;
+	-C*)
+		git_am_opt="$git_am_opt $1"
+		;;
+	--root)
+		rebase_root=t
+		;;
+	--force-rebase|--no-ff)
+		force_rebase=t
+		;;
+	--rerere-autoupdate|--no-rerere-autoupdate)
+		allow_rerere_autoupdate="$1"
+		;;
+	--gpg-sign)
+		gpg_sign_opt=-S
+		;;
+	--gpg-sign=*)
+		gpg_sign_opt="-S${1#--gpg-sign=}"
+		;;
+	--)
+		shift
+		break
+		;;
+	*)
+		usage
+		;;
+	esac
+	shift
+done
+test $# -gt 2 && usage
+
+if test -n "$action"
+then
+	test -z "$in_progress" && die "$(gettext "No rebase in progress?")"
+	# Only interactive rebase uses detailed reflog messages
+	if test -n "$interactive_rebase" && test "$GIT_REFLOG_ACTION" = rebase
+	then
+		GIT_REFLOG_ACTION="rebase -i ($action)"
+		export GIT_REFLOG_ACTION
+	fi
+fi
+
+if test "$action" = "edit-todo" && test -z "$interactive_rebase"
+then
+	die "$(gettext "The --edit-todo action can only be used during interactive rebase.")"
+fi
+
+case "$action" in
+continue)
+	# Sanity check
+	git rev-parse --verify HEAD >/dev/null ||
+		die "$(gettext "Cannot read HEAD")"
+	git update-index --ignore-submodules --refresh &&
+	git diff-files --quiet --ignore-submodules || {
+		echo "$(gettext "You must edit all merge conflicts and then
+mark them as resolved using git add")"
+		exit 1
+	}
+	read_basic_state
+	run_specific_rebase
+	;;
+skip)
+	output git reset --hard HEAD || exit $?
+	read_basic_state
+	run_specific_rebase
+	;;
+abort)
+	git rerere clear
+	read_basic_state
+	case "$head_name" in
+	refs/*)
+		git symbolic-ref -m "rebase: aborting" HEAD $head_name ||
+		die "$(eval_gettext "Could not move back to \$head_name")"
+		;;
+	esac
+	output git reset --hard $orig_head
+	finish_rebase
+	exit
+	;;
+quit)
+	exec rm -rf "$state_dir"
+	;;
+edit-todo)
+	run_specific_rebase
+	;;
+show-current-patch)
+	run_specific_rebase
+	die "BUG: run_specific_rebase is not supposed to return here"
+	;;
+esac
+
+# Make sure no rebase is in progress
+if test -n "$in_progress"
+then
+	state_dir_base=${state_dir##*/}
+	cmd_live_rebase="git rebase (--continue | --abort | --skip)"
+	cmd_clear_stale_rebase="rm -fr \"$state_dir\""
+	die "
+$(eval_gettext 'It seems that there is already a $state_dir_base directory, and
+I wonder if you are in the middle of another rebase.  If that is the
+case, please try
+	$cmd_live_rebase
+If that is not the case, please
+	$cmd_clear_stale_rebase
+and run me again.  I am stopping in case you still have something
+valuable there.')"
+fi
+
+if test -n "$rebase_root" && test -z "$onto"
+then
+	test -z "$interactive_rebase" && interactive_rebase=implied
+fi
+
+if test -n "$keep_empty"
+then
+	test -z "$interactive_rebase" && interactive_rebase=implied
+fi
+
+if test -n "$interactive_rebase"
+then
+	if test -z "$preserve_merges"
+	then
+		type=interactive
+	else
+		type=preserve-merges
+	fi
+
+	state_dir="$merge_dir"
+elif test -n "$do_merge"
+then
+	type=merge
+	state_dir="$merge_dir"
+else
+	type=am
+	state_dir="$apply_dir"
+fi
+
+if test -t 2 && test -z "$GIT_QUIET"
+then
+	git_format_patch_opt="$git_format_patch_opt --progress"
+fi
+
+if test -n "$signoff"
+then
+	test -n "$preserve_merges" &&
+		die "$(gettext "error: cannot combine '--signoff' with '--preserve-merges'")"
+	git_am_opt="$git_am_opt $signoff"
+	force_rebase=t
+fi
+
+if test -z "$rebase_root"
+then
+	case "$#" in
+	0)
+		if ! upstream_name=$(git rev-parse --symbolic-full-name \
+			--verify -q @{upstream} 2>/dev/null)
+		then
+			. git-parse-remote
+			error_on_missing_default_upstream "rebase" "rebase" \
+				"against" "git rebase $(gettext '<branch>')"
+		fi
+
+		test "$fork_point" = auto && fork_point=t
+		;;
+	*)	upstream_name="$1"
+		if test "$upstream_name" = "-"
+		then
+			upstream_name="@{-1}"
+		fi
+		shift
+		;;
+	esac
+	upstream=$(peel_committish "${upstream_name}") ||
+	die "$(eval_gettext "invalid upstream '\$upstream_name'")"
+	upstream_arg="$upstream_name"
+else
+	if test -z "$onto"
+	then
+		empty_tree=$(git hash-object -t tree /dev/null)
+		onto=$(git commit-tree $empty_tree </dev/null)
+		squash_onto="$onto"
+	fi
+	unset upstream_name
+	unset upstream
+	test $# -gt 1 && usage
+	upstream_arg=--root
+fi
+
+# Make sure the branch to rebase onto is valid.
+onto_name=${onto-"$upstream_name"}
+case "$onto_name" in
+*...*)
+	if	left=${onto_name%...*} right=${onto_name#*...} &&
+		onto=$(git merge-base --all ${left:-HEAD} ${right:-HEAD})
+	then
+		case "$onto" in
+		?*"$LF"?*)
+			die "$(eval_gettext "\$onto_name: there are more than one merge bases")"
+			;;
+		'')
+			die "$(eval_gettext "\$onto_name: there is no merge base")"
+			;;
+		esac
+	else
+		die "$(eval_gettext "\$onto_name: there is no merge base")"
+	fi
+	;;
+*)
+	onto=$(peel_committish "$onto_name") ||
+	die "$(eval_gettext "Does not point to a valid commit: \$onto_name")"
+	;;
+esac
+
+# If the branch to rebase is given, that is the branch we will rebase
+# $branch_name -- branch/commit being rebased, or HEAD (already detached)
+# $orig_head -- commit object name of tip of the branch before rebasing
+# $head_name -- refs/heads/<that-branch> or "detached HEAD"
+switch_to=
+case "$#" in
+1)
+	# Is it "rebase other $branchname" or "rebase other $commit"?
+	branch_name="$1"
+	switch_to="$1"
+
+	# Is it a local branch?
+	if git show-ref --verify --quiet -- "refs/heads/$branch_name" &&
+	   orig_head=$(git rev-parse -q --verify "refs/heads/$branch_name")
+	then
+		head_name="refs/heads/$branch_name"
+	# If not is it a valid ref (branch or commit)?
+	elif orig_head=$(git rev-parse -q --verify "$branch_name")
+	then
+		head_name="detached HEAD"
+
+	else
+		die "$(eval_gettext "fatal: no such branch/commit '\$branch_name'")"
+	fi
+	;;
+0)
+	# Do not need to switch branches, we are already on it.
+	if branch_name=$(git symbolic-ref -q HEAD)
+	then
+		head_name=$branch_name
+		branch_name=$(expr "z$branch_name" : 'zrefs/heads/\(.*\)')
+	else
+		head_name="detached HEAD"
+		branch_name=HEAD
+	fi
+	orig_head=$(git rev-parse --verify HEAD) || exit
+	;;
+*)
+	die "BUG: unexpected number of arguments left to parse"
+	;;
+esac
+
+if test "$fork_point" = t
+then
+	new_upstream=$(git merge-base --fork-point "$upstream_name" \
+			"${switch_to:-HEAD}")
+	if test -n "$new_upstream"
+	then
+		restrict_revision=$new_upstream
+	fi
+fi
+
+if test "$autostash" = true && ! (require_clean_work_tree) 2>/dev/null
+then
+	stash_sha1=$(git stash create "autostash") ||
+	die "$(gettext 'Cannot autostash')"
+
+	mkdir -p "$state_dir" &&
+	echo $stash_sha1 >"$state_dir/autostash" &&
+	stash_abbrev=$(git rev-parse --short $stash_sha1) &&
+	echo "$(eval_gettext 'Created autostash: $stash_abbrev')" &&
+	git reset --hard
+fi
+
+require_clean_work_tree "rebase" "$(gettext "Please commit or stash them.")"
+
+# Now we are rebasing commits $upstream..$orig_head (or with --root,
+# everything leading up to $orig_head) on top of $onto
+
+# Check if we are already based on $onto with linear history,
+# but this should be done only when upstream and onto are the same
+# and if this is not an interactive rebase.
+mb=$(git merge-base "$onto" "$orig_head")
+if test -z "$interactive_rebase" && test "$upstream" = "$onto" &&
+	test "$mb" = "$onto" && test -z "$restrict_revision" &&
+	# linear history?
+	! (git rev-list --parents "$onto".."$orig_head" | sane_grep " .* ") > /dev/null
+then
+	if test -z "$force_rebase"
+	then
+		# Lazily switch to the target branch if needed...
+		test -z "$switch_to" ||
+		GIT_REFLOG_ACTION="$GIT_REFLOG_ACTION: checkout $switch_to" \
+			git checkout -q "$switch_to" --
+		if test "$branch_name" = "HEAD" &&
+			 ! git symbolic-ref -q HEAD
+		then
+			say "$(eval_gettext "HEAD is up to date.")"
+		else
+			say "$(eval_gettext "Current branch \$branch_name is up to date.")"
+		fi
+		finish_rebase
+		exit 0
+	else
+		if test "$branch_name" = "HEAD" &&
+			 ! git symbolic-ref -q HEAD
+		then
+			say "$(eval_gettext "HEAD is up to date, rebase forced.")"
+		else
+			say "$(eval_gettext "Current branch \$branch_name is up to date, rebase forced.")"
+		fi
+	fi
+fi
+
+# If a hook exists, give it a chance to interrupt
+run_pre_rebase_hook "$upstream_arg" "$@"
+
+if test -n "$diffstat"
+then
+	if test -n "$verbose"
+	then
+		echo "$(eval_gettext "Changes from \$mb to \$onto:")"
+	fi
+	# We want color (if set), but no pager
+	GIT_PAGER='' git diff --stat --summary "$mb" "$onto"
+fi
+
+test -n "$interactive_rebase" && run_specific_rebase
+
+# Detach HEAD and reset the tree
+say "$(gettext "First, rewinding head to replay your work on top of it...")"
+
+GIT_REFLOG_ACTION="$GIT_REFLOG_ACTION: checkout $onto_name" \
+	git checkout -q "$onto^0" || die "could not detach HEAD"
+git update-ref ORIG_HEAD $orig_head
+
+# If the $onto is a proper descendant of the tip of the branch, then
+# we just fast-forwarded.
+if test "$mb" = "$orig_head"
+then
+	say "$(eval_gettext "Fast-forwarded \$branch_name to \$onto_name.")"
+	move_to_original_branch
+	finish_rebase
+	exit 0
+fi
+
+if test -n "$rebase_root"
+then
+	revisions="$onto..$orig_head"
+else
+	revisions="${restrict_revision-$upstream}..$orig_head"
+fi
+
+run_specific_rebase

@@ -78,6 +78,7 @@
 /git-init-db
 /git-interpret-trailers
 /git-instaweb
+/git-legacy-rebase
 /git-log
 /git-ls-files
 /git-ls-remote

@@ -609,7 +609,7 @@ SCRIPT_SH += git-merge-one-file.sh
 SCRIPT_SH += git-merge-resolve.sh
 SCRIPT_SH += git-mergetool.sh
 SCRIPT_SH += git-quiltimport.sh
-SCRIPT_SH += git-rebase.sh
+SCRIPT_SH += git-legacy-rebase.sh
 SCRIPT_SH += git-remote-testgit.sh
 SCRIPT_SH += git-request-pull.sh
 SCRIPT_SH += git-stash.sh

@@ -1059,6 +1059,7 @@ BUILTIN_OBJS += builtin/prune.o
 BUILTIN_OBJS += builtin/pull.o
 BUILTIN_OBJS += builtin/push.o
 BUILTIN_OBJS += builtin/read-tree.o
+BUILTIN_OBJS += builtin/rebase.o
 BUILTIN_OBJS += builtin/rebase--helper.o
 BUILTIN_OBJS += builtin/receive-pack.o
 BUILTIN_OBJS += builtin/reflog.o

@@ -202,6 +202,7 @@ extern int cmd_prune_packed(int argc, const char **argv, const char *prefix);
 extern int cmd_pull(int argc, const char **argv, const char *prefix);
 extern int cmd_push(int argc, const char **argv, const char *prefix);
 extern int cmd_read_tree(int argc, const char **argv, const char *prefix);
+extern int cmd_rebase(int argc, const char **argv, const char *prefix);
 extern int cmd_rebase__helper(int argc, const char **argv, const char *prefix);
 extern int cmd_receive_pack(int argc, const char **argv, const char *prefix);
 extern int cmd_reflog(int argc, const char **argv, const char *prefix);

@@ -0,0 +1,55 @@
+/*
+ * "git rebase" builtin command
+ *
+ * Copyright (c) 2018 Pratik Karki
+ */
+
+#include "builtin.h"
+#include "run-command.h"
+#include "exec-cmd.h"
+#include "argv-array.h"
+#include "dir.h"
+
+static int use_builtin_rebase(void)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf out = STRBUF_INIT;
+	int ret;
+
+	argv_array_pushl(&cp.args,
+			 "config", "--bool", "rebase.usebuiltin", NULL);
+	cp.git_cmd = 1;
+	if (capture_command(&cp, &out, 6))
+		return 0;
+
+	strbuf_trim(&out);
+	ret = !strcmp("true", out.buf);
+	strbuf_release(&out);
+	return ret;
+}
+
+int cmd_rebase(int argc, const char **argv, const char *prefix)
+{
+	/*
+	* NEEDSWORK: Once the builtin rebase has been tested enough
+	* and git-legacy-rebase.sh is retired to contrib/, this preamble
+	* can be removed.
+	*/
+	if (!use_builtin_rebase()) {
+		const char *path = mkpath("%s/git-legacy-rebase",
+					  git_exec_path());
+
+		if (sane_execvp(path, (char **)argv) < 0)
+			die_errno("could not exec %s", path);
+
+		return 0;
+	}
+
+	if (argc != 2)
+		die("Usage: %s <base>", argv[0]);
+	prefix = setup_git_directory();
+	trace_repo_setup(prefix);
+	setup_work_tree();
+
+	die("TODO");
+}

@@ -518,6 +518,12 @@ static struct cmd_struct commands[] = {
 	{ "pull", cmd_pull, RUN_SETUP | NEED_WORK_TREE },
 	{ "push", cmd_push, RUN_SETUP },
 	{ "read-tree", cmd_read_tree, RUN_SETUP | SUPPORT_SUPER_PREFIX},
+	/*
+	 *NEEDSWORK: Until the rebase is independent and needs no redirection
+	 to rebase shell script this is kept as is, then should be changed to
+	 RUN_SETUP | NEED_WORK_TREE
+	*/
+	{ "rebase", cmd_rebase },
 	{ "rebase--helper", cmd_rebase__helper, RUN_SETUP | NEED_WORK_TREE },
 	{ "receive-pack", cmd_receive_pack },
 	{ "reflog", cmd_reflog, RUN_SETUP },

@@ -117,6 +117,7 @@
 /git-read-tree
 /git-rebase
 /git-rebase--am
+/git-rebase--common
 /git-rebase--helper
 /git-rebase--interactive
 /git-rebase--merge

@@ -619,6 +619,7 @@ SCRIPT_SH += git-web--browse.sh
 SCRIPT_LIB += git-mergetool--lib
 SCRIPT_LIB += git-parse-remote
 SCRIPT_LIB += git-rebase--am
+SCRIPT_LIB += git-rebase--common
 SCRIPT_LIB += git-rebase--interactive
 SCRIPT_LIB += git-rebase--preserve-merges
 SCRIPT_LIB += git-rebase--merge

@@ -102,6 +102,7 @@ case "$(git config --bool commit.gpgsign)" in
 true)	gpg_sign_opt=-S ;;
 *)	gpg_sign_opt= ;;
 esac
+. git-rebase--common
 
 read_basic_state () {
 	test -f "$state_dir/head-name" &&

@@ -132,67 +133,6 @@ read_basic_state () {
 	}
 }
 
-write_basic_state () {
-	echo "$head_name" > "$state_dir"/head-name &&
-	echo "$onto" > "$state_dir"/onto &&
-	echo "$orig_head" > "$state_dir"/orig-head &&
-	echo "$GIT_QUIET" > "$state_dir"/quiet &&
-	test t = "$verbose" && : > "$state_dir"/verbose
-	test -n "$strategy" && echo "$strategy" > "$state_dir"/strategy
-	test -n "$strategy_opts" && echo "$strategy_opts" > \
-		"$state_dir"/strategy_opts
-	test -n "$allow_rerere_autoupdate" && echo "$allow_rerere_autoupdate" > \
-		"$state_dir"/allow_rerere_autoupdate
-	test -n "$gpg_sign_opt" && echo "$gpg_sign_opt" > "$state_dir"/gpg_sign_opt
-	test -n "$signoff" && echo "$signoff" >"$state_dir"/signoff
-}
-
-output () {
-	case "$verbose" in
-	'')
-		output=$("$@" 2>&1 )
-		status=$?
-		test $status != 0 && printf "%s\n" "$output"
-		return $status
-		;;
-	*)
-		"$@"
-		;;
-	esac
-}
-
-move_to_original_branch () {
-	case "$head_name" in
-	refs/*)
-		message="rebase finished: $head_name onto $onto"
-		git update-ref -m "$message" \
-			$head_name $(git rev-parse HEAD) $orig_head &&
-		git symbolic-ref \
-			-m "rebase finished: returning to $head_name" \
-			HEAD $head_name ||
-		die "$(eval_gettext "Could not move back to \$head_name")"
-		;;
-	esac
-}
-
-apply_autostash () {
-	if test -f "$state_dir/autostash"
-	then
-		stash_sha1=$(cat "$state_dir/autostash")
-		if git stash apply $stash_sha1 >/dev/null 2>&1
-		then
-			echo "$(gettext 'Applied autostash.')" >&2
-		else
-			git stash store -m "autostash" -q $stash_sha1 ||
-			die "$(eval_gettext "Cannot store \$stash_sha1")"
-			gettext 'Applying autostash resulted in conflicts.
-Your changes are safe in the stash.
-You can run "git stash pop" or "git stash drop" at any time.
-' >&2
-		fi
-	fi
-}
-
 finish_rebase () {
 	rm -f "$(git rev-parse --git-path REBASE_HEAD)"
 	apply_autostash &&

@@ -0,0 +1,61 @@
+
+write_basic_state () {
+	echo "$head_name" > "$state_dir"/head-name &&
+	echo "$onto" > "$state_dir"/onto &&
+	echo "$orig_head" > "$state_dir"/orig-head &&
+	echo "$GIT_QUIET" > "$state_dir"/quiet &&
+	test t = "$verbose" && : > "$state_dir"/verbose
+	test -n "$strategy" && echo "$strategy" > "$state_dir"/strategy
+	test -n "$strategy_opts" && echo "$strategy_opts" > \
+		"$state_dir"/strategy_opts
+	test -n "$allow_rerere_autoupdate" && echo "$allow_rerere_autoupdate" > \
+		"$state_dir"/allow_rerere_autoupdate
+	test -n "$gpg_sign_opt" && echo "$gpg_sign_opt" > "$state_dir"/gpg_sign_opt
+	test -n "$signoff" && echo "$signoff" >"$state_dir"/signoff
+}
+
+apply_autostash () {
+	if test -f "$state_dir/autostash"
+	then
+		stash_sha1=$(cat "$state_dir/autostash")
+		if git stash apply $stash_sha1 >/dev/null 2>&1
+		then
+			echo "$(gettext 'Applied autostash.')" >&2
+		else
+			git stash store -m "autostash" -q $stash_sha1 ||
+			die "$(eval_gettext "Cannot store \$stash_sha1")"
+			gettext 'Applying autostash resulted in conflicts.
+Your changes are safe in the stash.
+You can run "git stash pop" or "git stash drop" at any time.
+' >&2
+		fi
+	fi
+}
+
+move_to_original_branch () {
+	case "$head_name" in
+	refs/*)
+		message="rebase finished: $head_name onto $onto"
+		git update-ref -m "$message" \
+			$head_name $(git rev-parse HEAD) $orig_head &&
+		git symbolic-ref \
+			-m "rebase finished: returning to $head_name" \
+			HEAD $head_name ||
+		die "$(eval_gettext "Could not move back to \$head_name")"
+		;;
+	esac
+}
+
+output () {
+	case "$verbose" in
+	'')
+		output=$("$@" 2>&1 )
+		status=$?
+		test $status != 0 && printf "%s\n" "$output"
+		return $status
+		;;
+	*)
+		"$@"
+		;;
+	esac
+}

@@ -2,6 +2,11 @@
 #include "remote.h"
 #include "refspec.h"
 #include "checkout.h"
+#include "unpack-trees.h"
+#include "lockfile.h"
+#include "refs.h"
+#include "tree.h"
+#include "cache-tree.h"
 
 struct tracking_name_data {
 	/* const */ char *src_ref;

@@ -42,3 +47,62 @@ const char *unique_tracking_name(const char *name, struct object_id *oid)
 	free(cb_data.dst_ref);
 	return NULL;
 }
+
+int detach_head_to(struct object_id *oid, const char *action,
+		   const char *reflog_message)
+{
+	struct strbuf ref_name = STRBUF_INIT;
+	struct tree_desc desc;
+	struct lock_file lock = LOCK_INIT;
+	struct unpack_trees_options unpack_tree_opts;
+	struct tree *tree;
+	int ret = 0;
+
+	if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0)
+		return -1;
+
+	memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
+	setup_unpack_trees_porcelain(&unpack_tree_opts, action);
+	unpack_tree_opts.head_idx = 1;
+	unpack_tree_opts.src_index = &the_index;
+	unpack_tree_opts.dst_index = &the_index;
+	unpack_tree_opts.fn = oneway_merge;
+	unpack_tree_opts.merge = 1;
+	unpack_tree_opts.update = 1;
+
+	if (read_cache_unmerged()) {
+		rollback_lock_file(&lock);
+		strbuf_release(&ref_name);
+		return error_resolve_conflict(_(action));
+	}
+
+	if (!fill_tree_descriptor(&desc, oid)) {
+		error(_("failed to find tree of %s"), oid_to_hex(oid));
+		rollback_lock_file(&lock);
+		free((void *)desc.buffer);
+		strbuf_release(&ref_name);
+		return -1;
+	}
+
+	if (unpack_trees(1, &desc, &unpack_tree_opts)) {
+		rollback_lock_file(&lock);
+		free((void *)desc.buffer);
+		strbuf_release(&ref_name);
+		return -1;
+	}
+
+	tree = parse_tree_indirect(oid);
+	prime_cache_tree(&the_index, tree);
+
+	if (write_locked_index(&the_index, &lock, COMMIT_LOCK) < 0)
+		ret = error(_("could not write index"));
+	free((void *)desc.buffer);
+
+	if (!ret)
+		ret = update_ref(reflog_message, "HEAD", oid,
+				 NULL, 0, UPDATE_REFS_MSG_ON_ERR);
+
+	strbuf_release(&ref_name);
+	return ret;
+
+}

@@ -10,4 +10,7 @@
  */
 extern const char *unique_tracking_name(const char *name, struct object_id *oid);
 
+int detach_head_to(struct object_id *oid, const char *action,
+		   const char *reflog_message);
+
 #endif /* CHECKOUT_H */

@@ -29,6 +29,7 @@
 #include "oidset.h"
 #include "commit-slab.h"
 #include "alias.h"
+#include "checkout.h"
 
 #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
 

@@ -2756,14 +2757,7 @@ static int do_reset(const char *name, int len, struct replay_opts *opts)
 {
 	struct strbuf ref_name = STRBUF_INIT;
 	struct object_id oid;
-	struct lock_file lock = LOCK_INIT;
-	struct tree_desc desc;
-	struct tree *tree;
-	struct unpack_trees_options unpack_tree_opts;
-	int ret = 0, i;
-
-	if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0)
-		return -1;
+	int i;
 
 	if (len == 10 && !strncmp("[new root]", name, len)) {
 		if (!opts->have_squash_onto) {