rebase: add --quit to cleanup rebase, leave everything else untouched

There are occasions when you decide to abort an in-progress rebase and
move on to do something else but you forget to do "git rebase --abort"
first. Or the rebase has been in progress for so long you forgot about
it. By the time you realize that (e.g. by starting another rebase)
it's already too late to retrace your steps. The solution is normally

    rm -r .git/<some rebase dir>

and continue with your life. But there could be two different
directories for <some rebase dir> (and it obviously requires some
knowledge of how rebase works), and the ".git" part could be much
longer if you are not at top-dir, or in a linked worktree. And
"rm -r" is very dangerous to do in .git, a mistake in there could
destroy object database or other important data.

Provide "git rebase --quit" for this use case, mimicking a precedent
that is "git cherry-pick --quit".

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -12,7 +12,7 @@ SYNOPSIS
 	[<upstream> [<branch>]]
 'git rebase' [-i | --interactive] [options] [--exec <cmd>] [--onto <newbase>]
 	--root [<branch>]
-'git rebase' --continue | --skip | --abort | --edit-todo
+'git rebase' --continue | --skip | --abort | --quit | --edit-todo
 
 DESCRIPTION
 -----------
@@ -252,6 +252,11 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 	will be reset to where it was when the rebase operation was
 	started.
 
+--quit::
+	Abort the rebase operation but HEAD is not reset back to the
+	original branch. The index and working tree are also left
+	unchanged as a result.
+
 --keep-empty::
 	Keep the commits that do not change anything from its
 	parents in the result.

contrib/completion/git-completion.bash

@@ -1670,10 +1670,10 @@ _git_rebase ()
 {
 	local dir="$(__gitdir)"
 	if [ -f "$dir"/rebase-merge/interactive ]; then
-		__gitcomp "--continue --skip --abort --edit-todo"
+		__gitcomp "--continue --skip --abort --quit --edit-todo"
 		return
 	elif [ -d "$dir"/rebase-apply ] || [ -d "$dir"/rebase-merge ]; then
-		__gitcomp "--continue --skip --abort"
+		__gitcomp "--continue --skip --abort --quit"
 		return
 	fi
 	__git_complete_strategy && return

git-rebase.sh

@@ -43,6 +43,7 @@ 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
 "
 . git-sh-setup
 . git-sh-i18n
@@ -239,7 +240,7 @@ do
 	--verify)
 		ok_to_skip_pre_rebase=
 		;;
-	--continue|--skip|--abort|--edit-todo)
+	--continue|--skip|--abort|--quit|--edit-todo)
 		test $total_argc -eq 2 || usage
 		action=${1##--}
 		;;
@@ -402,6 +403,9 @@ abort)
 	finish_rebase
 	exit
 	;;
+quit)
+	exec rm -rf "$state_dir"
+	;;
 edit-todo)
 	run_specific_rebase
 	;;

t/t3407-rebase-abort.sh

@@ -99,4 +99,28 @@ testrebase() {
 testrebase "" .git/rebase-apply
 testrebase " --merge" .git/rebase-merge
 
+test_expect_success 'rebase --quit' '
+	cd "$work_dir" &&
+	# Clean up the state from the previous one
+	git reset --hard pre-rebase &&
+	test_must_fail git rebase master &&
+	test_path_is_dir .git/rebase-apply &&
+	head_before=$(git rev-parse HEAD) &&
+	git rebase --quit &&
+	test $(git rev-parse HEAD) = $head_before &&
+	test ! -d .git/rebase-apply
+'
+
+test_expect_success 'rebase --merge --quit' '
+	cd "$work_dir" &&
+	# Clean up the state from the previous one
+	git reset --hard pre-rebase &&
+	test_must_fail git rebase --merge master &&
+	test_path_is_dir .git/rebase-merge &&
+	head_before=$(git rev-parse HEAD) &&
+	git rebase --quit &&
+	test $(git rev-parse HEAD) = $head_before &&
+	test ! -d .git/rebase-merge
+'
+
 test_done