sequencer: add update-ref command

Add the boilerplate for an "update-ref" command in the sequencer. This
connects to the current no-op do_update_ref() which will be filled in
after more connections are created.

The syntax in the todo list will be "update-ref <ref-name>" to signal
that we should store the current commit as the value for updating
<ref-name> at the end of the rebase.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

rebase-interactive.c

@@ -57,6 +57,9 @@ void append_todo_help(int command_count,
 "        create a merge commit using the original merge commit's\n"
 "        message (or the oneline, if no original merge commit was\n"
 "        specified); use -c <commit> to reword the commit message\n"
+"u, update-ref <ref> = track a placeholder for the <ref> to be updated\n"
+"                      to this position in the new commits. The <ref> is\n"
+"                      updated at the end of the rebase\n"
 "\n"
 "These lines can be re-ordered; they are executed from top to bottom.\n");
 	unsigned edit_todo = !(shortrevisions && shortonto);

sequencer.c

@@ -1723,6 +1723,7 @@ static struct {
 	[TODO_LABEL] = { 'l', "label" },
 	[TODO_RESET] = { 't', "reset" },
 	[TODO_MERGE] = { 'm', "merge" },
+	[TODO_UPDATE_REF] = { 'u', "update-ref" },
 	[TODO_NOOP] = { 0,   "noop" },
 	[TODO_DROP] = { 'd', "drop" },
 	[TODO_COMMENT] = { 0,   NULL },
@@ -2504,7 +2505,7 @@ static int parse_insn_line(struct repository *r, struct todo_item *item,
 			     command_to_string(item->command));
 
 	if (item->command == TODO_EXEC || item->command == TODO_LABEL ||
-	    item->command == TODO_RESET) {
+	    item->command == TODO_RESET || item->command == TODO_UPDATE_REF) {
 		item->commit = NULL;
 		item->arg_offset = bol - buf;
 		item->arg_len = (int)(eol - bol);
@@ -4104,6 +4105,11 @@ leave_merge:
 	return ret;
 }
 
+static int do_update_ref(struct repository *r, const char *ref_name)
+{
+	return 0;
+}
+
 static int is_final_fixup(struct todo_list *todo_list)
 {
 	int i = todo_list->current;
@@ -4479,6 +4485,12 @@ static int pick_commits(struct repository *r,
 				return error_with_patch(r, item->commit,
 							arg, item->arg_len,
 							opts, res, 0);
+		} else if (item->command == TODO_UPDATE_REF) {
+			struct strbuf ref = STRBUF_INIT;
+			strbuf_add(&ref, arg, item->arg_len);
+			if ((res = do_update_ref(r, ref.buf)))
+				reschedule = 1;
+			strbuf_release(&ref);
 		} else if (!is_noop(item->command))
 			return error(_("unknown command %d"), item->command);
 

sequencer.h

@@ -96,6 +96,7 @@ enum todo_command {
 	TODO_LABEL,
 	TODO_RESET,
 	TODO_MERGE,
+	TODO_UPDATE_REF,
 	/* commands that do nothing but are counted for reporting progress */
 	TODO_NOOP,
 	TODO_DROP,