rebase: implement --[no-]autostash and rebase.autostash

This new feature allows a rebase to be executed on a dirty worktree or
index.  It works by creating a temporary "dangling merge commit" out
of the worktree and index changes (via 'git stash create'), and
automatically applying it after a successful rebase or abort.

rebase stores the SHA-1 hex of the temporary merge commit, along with
the rest of the rebase state, in either
.git/{rebase-merge,rebase-apply}/autostash depending on the kind of
rebase.  Since $state_dir is automatically removed at the end of a
successful rebase or abort, so is the autostash.

The advantage of this approach is that we do not affect the normal
stash's reflogs, making the autostash invisible to the end-user.  This
means that you can use 'git stash' during a rebase as usual.

When the autostash application results in a conflict, we push
$state_dir/autostash onto the normal stash and remove $state_dir
ending the rebase.  The user can inspect the stash, and pop or drop at
any time.

Most significantly, this feature means that a caller like pull (with
pull.rebase set to true) can easily be patched to remove the
require_clean_work_tree restriction.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 42 insertions, 3 deletions

diff --git a/git-rebase.sh b/git-rebase.sh
index f8b533d183..d0c11a910a 100755
--- a/git-rebase.sh
+++ b/git-rebase.sh
@@ -13,6 +13,7 @@ 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
 onto=!             rebase onto given branch instead of upstream
 p,preserve-merges! try to recreate merges instead of ignoring them
 s,strategy=!       use the given merge strategy
@@ -64,6 +65,7 @@ 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)"
 git_am_opt=
 rebase_root=
 force_rebase=
@@ -143,6 +145,29 @@ move_to_original_branch () {
 	esac
 }
 
+finish_rebase () {
+	if test -f "$state_dir/autostash"
+	then
+		stash_sha1=$(cat "$state_dir/autostash")
+		if git stash apply $stash_sha1 2>&1 >/dev/null
+		then
+			echo "$(gettext 'Applied autostash.')"
+		else
+			ref_stash=refs/stash &&
+			>>"$GIT_DIR/logs/$ref_stash" &&
+			git update-ref -m "autostash" $ref_stash $stash_sha1 ||
+			die "$(eval_gettext 'Cannot store $stash_sha1')"
+
+			gettext 'Applying autostash resulted in conflicts.
+Your changes are safe in the stash.
+You can run "git stash pop" or "git stash drop" it at any time.
+'
+		fi
+	fi
+	git gc --auto &&
+	rm -rf "$state_dir"
+}
+
 run_specific_rebase () {
 	if [ "$interactive_rebase" = implied ]; then
 		GIT_EDITOR=:
@@ -153,8 +178,7 @@ run_specific_rebase () {
 	ret=$?
 	if test $ret -eq 0
 	then
-		git gc --auto &&
-		rm -rf "$state_dir"
+		finish_rebase
 	fi
 	exit $ret
 }
@@ -248,6 +272,9 @@ do
 	--stat)
 		diffstat=t
 		;;
+	--autostash)
+		autostash=true
+		;;
 	-v)
 		verbose=t
 		diffstat=t
@@ -348,7 +375,7 @@ abort)
 		;;
 	esac
 	output git reset --hard $orig_head
-	rm -r "$state_dir"
+	finish_rebase
 	exit
 	;;
 edit-todo)
@@ -487,6 +514,18 @@ case "$#" in
 	;;
 esac
 
+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,