Signed-off-by: Johannes Schindelin <redacted>
---
 git-rebase--interactive.sh |   3 +
 sequencer.c                | 181 ++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 180 insertions(+), 4 deletions(-)

diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index d47bd29593a..3d2cd19d65a 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh

@@ -162,6 +162,9 @@ 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
 d, drop = remove commit
+l, label = label current HEAD with a name
+t, reset = reset HEAD to a label
+b, bud = reset HEAD to the revision labeled 'onto'
 
 These lines can be re-ordered; they are executed from top to bottom.
 " | git stripspace --comment-lines >>"$todo"

diff --git a/sequencer.c b/sequencer.c
index 4d3f60594cb..91cc55a002f 100644
--- a/sequencer.c
+++ b/sequencer.c

@@ -21,6 +21,8 @@
 #include "log-tree.h"
 #include "wt-status.h"
 #include "hashmap.h"
+#include "unpack-trees.h"
+#include "worktree.h"
 
 #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
 

@@ -116,6 +118,13 @@ static GIT_PATH_FUNC(rebase_path_stopped_sha, "rebase-merge/stopped-sha")
 static GIT_PATH_FUNC(rebase_path_rewritten_list, "rebase-merge/rewritten-list")
 static GIT_PATH_FUNC(rebase_path_rewritten_pending,
 	"rebase-merge/rewritten-pending")
+
+/*
+ * The path of the file listing refs that need to be deleted after the rebase
+ * finishes. This is used by the `merge` command.
+ */
+static GIT_PATH_FUNC(rebase_path_refs_to_delete, "rebase-merge/refs-to-delete")
+
 /*
  * The following files are written by git-rebase just after parsing the
  * command-line (and are only consumed, not modified, by the sequencer).

@@ -767,6 +776,9 @@ enum todo_command {
 	TODO_SQUASH,
 	/* commands that do something else than handling a single commit */
 	TODO_EXEC,
+	TODO_LABEL,
+	TODO_RESET,
+	TODO_BUD,
 	/* commands that do nothing but are counted for reporting progress */
 	TODO_NOOP,
 	TODO_DROP,

@@ -785,6 +797,9 @@ static struct {
 	{ 'f', "fixup" },
 	{ 's', "squash" },
 	{ 'x', "exec" },
+	{ 'l', "label" },
+	{ 't', "reset" },
+	{ 'b', "bud" },
 	{ 0,   "noop" },
 	{ 'd', "drop" },
 	{ 0,   NULL }

@@ -1253,7 +1268,8 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 		if (skip_prefix(bol, todo_command_info[i].str, &bol)) {
 			item->command = i;
 			break;
-		} else if (bol[1] == ' ' && *bol == todo_command_info[i].c) {
+		} else if ((bol + 1 == eol || bol[1] == ' ') &&
+			   *bol == todo_command_info[i].c) {
 			bol++;
 			item->command = i;
 			break;

@@ -1265,7 +1281,7 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 	padding = strspn(bol, " \t");
 	bol += padding;
 
-	if (item->command == TODO_NOOP) {
+	if (item->command == TODO_NOOP || item->command == TODO_BUD) {
 		if (bol != eol)
 			return error(_("%s does not accept arguments: '%s'"),
 				     command_to_string(item->command), bol);

@@ -1279,7 +1295,8 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 		return error(_("missing arguments for %s"),
 			     command_to_string(item->command));
 
-	if (item->command == TODO_EXEC) {
+	if (item->command == TODO_EXEC || item->command == TODO_LABEL ||
+	    item->command == TODO_RESET) {
 		item->commit = NULL;
 		item->arg = bol;
 		item->arg_len = (int)(eol - bol);

@@ -1919,6 +1936,139 @@ static int do_exec(const char *command_line)
 	return status;
 }
 
+static int safe_append(const char *filename, const char *fmt, ...)
+{
+	va_list ap;
+	struct lock_file lock = LOCK_INIT;
+	int fd = hold_lock_file_for_update(&lock, filename, 0);
+	struct strbuf buf = STRBUF_INIT;
+
+	if (fd < 0)
+		return error_errno(_("could not lock '%s'"), filename);
+
+	if (strbuf_read_file(&buf, filename, 0) < 0 && errno != ENOENT)
+		return error_errno(_("could not read '%s'"), filename);
+	strbuf_complete(&buf, '\n');
+	va_start(ap, fmt);
+	strbuf_vaddf(&buf, fmt, ap);
+	va_end(ap);
+
+	if (write_in_full(fd, buf.buf, buf.len) < 0) {
+		rollback_lock_file(&lock);
+		return error_errno(_("could not write to '%s'"), filename);
+	}
+	if (commit_lock_file(&lock) < 0) {
+		rollback_lock_file(&lock);
+		return error(_("failed to finalize '%s'."), filename);
+	}
+
+	return 0;
+}
+
+static int do_label(const char *name, int len)
+{
+	struct ref_store *refs = get_main_ref_store();
+	struct ref_transaction *transaction;
+	struct strbuf ref_name = STRBUF_INIT, err = STRBUF_INIT;
+	struct strbuf msg = STRBUF_INIT;
+	int ret = 0;
+	struct object_id head_oid;
+
+	strbuf_addf(&ref_name, "refs/rewritten/%.*s", len, name);
+	strbuf_addf(&msg, "label '%.*s'", len, name);

+
+	strbuf_addf(&ref_name, "refs/rewritten/%.*s", len, name);
+	if (get_oid(ref_name.buf, &oid) &&
+	    get_oid(ref_name.buf + strlen("refs/rewritten/"), &oid)) {
+		error(_("could not read '%s'"), ref_name.buf);
+		rollback_lock_file(&lock);
+		strbuf_release(&ref_name);
+		return -1;
+	}
+
+	memset(&opts, 0, sizeof(opts));
+	opts.head_idx = 1;
+	opts.src_index = &the_index;
+	opts.dst_index = &the_index;
+	opts.fn = oneway_merge;
+	opts.merge = 1;
+	opts.update = 1;
+	opts.reset = 1;
+
+	read_cache_unmerged();
+	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, &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) {
+		struct strbuf msg = STRBUF_INIT;
+
+		strbuf_addf(&msg, "(rebase -i) reset '%.*s'", len, name);
+		ret = update_ref(msg.buf, "HEAD", &oid, NULL, 0,
+				 UPDATE_REFS_MSG_ON_ERR);
+		strbuf_release(&msg);
+	}
+
+	strbuf_release(&ref_name);
+	return ret;
+}
+
 static int is_final_fixup(struct todo_list *todo_list)
 {
 	int i = todo_list->current;

@@ -2102,7 +2252,13 @@ static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 				/* `current` will be incremented below */
 				todo_list->current = -1;
 			}
-		} else if (!is_noop(item->command))
+		} else if (item->command == TODO_LABEL)
+			res = do_label(item->arg, item->arg_len);
+		else if (item->command == TODO_RESET)
+			res = do_reset(item->arg, item->arg_len);
+		else if (item->command == TODO_BUD)
+			res = do_reset("onto", 4);
+		else if (!is_noop(item->command))
 			return error(_("unknown command %d"), item->command);
 
 		todo_list->current++;

@@ -2207,6 +2363,23 @@ static int pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
 		}
 		apply_autostash(opts);
 
+		strbuf_reset(&buf);
+		if (strbuf_read_file(&buf, rebase_path_refs_to_delete(), 0)
+		    > 0) {
+			char *p = buf.buf;
+			while (*p) {
+				char *eol = strchr(p, '\n');
+				if (eol)
+					*eol = '\0';
+				if (delete_ref("(rebase -i) cleanup",
+					       p, NULL, 0) < 0)
+					warning(_("could not delete '%s'"), p);
+				if (!eol)
+					break;
+				p = eol + 1;
+			}
+		}
+
 		fprintf(stderr, "Successfully rebased and updated %s.\n",
 			head_ref.buf);