sequencer: support a new action: 'interactive rebase'

This patch introduces a new action for the sequencer. It really does not
do a whole lot of its own right now, but lays the ground work for
patches to come. The intention, of course, is to finally make the
sequencer the work horse of the interactive rebase (the original idea
behind the "sequencer" concept).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

sequencer.c

@@ -27,13 +27,28 @@ static GIT_PATH_FUNC(git_path_todo_file, "sequencer/todo")
 static GIT_PATH_FUNC(git_path_opts_file, "sequencer/opts")
 static GIT_PATH_FUNC(git_path_head_file, "sequencer/head")
 
+static GIT_PATH_FUNC(git_path_rebase_dir, "rebase-merge")
+/*
+ * The file containing rebase commands, comments, and empty lines.
+ * This file is created by "git rebase -i" then edited by the user. As
+ * the lines are processed, they are removed from the front of this
+ * file and written to the tail of 'done'.
+ */
+static GIT_PATH_FUNC(git_path_rebase_todo, "rebase-merge/git-rebase-todo")
+
+#define IS_REBASE_I() (opts->action == REPLAY_INTERACTIVE_REBASE)
+
 static const char *get_dir(const struct replay_opts *opts)
 {
+	if (IS_REBASE_I())
+		return git_path_rebase_dir();
 	return git_path_seq_dir();
 }
 
 static const char *get_todo_path(const struct replay_opts *opts)
 {
+	if (IS_REBASE_I())
+		return git_path_rebase_todo();
 	return git_path_todo_file();
 }
 
@@ -130,7 +145,15 @@ static void remove_sequencer_state(const struct replay_opts *opts)
 
 static const char *action_name(const struct replay_opts *opts)
 {
-	return opts->action == REPLAY_REVERT ? "revert" : "cherry-pick";
+	switch (opts->action) {
+	case REPLAY_REVERT:
+		return "revert";
+	case REPLAY_PICK:
+		return "cherry-pick";
+	case REPLAY_INTERACTIVE_REBASE:
+		return "rebase -i";
+	}
+	die("Unknown action: %d", opts->action);
 }
 
 struct commit_message {
@@ -310,7 +333,10 @@ static int do_recursive_merge(struct commit *base, struct commit *next,
 
 	if (active_cache_changed &&
 	    write_locked_index(&the_index, &index_lock, COMMIT_LOCK))
-		/* TRANSLATORS: %s will be "revert" or "cherry-pick" */
+		/*
+		 * TRANSLATORS: %s will be "revert", "cherry-pick" or
+		 * "rebase -i".
+		 */
 		return error(_("%s: Unable to write new index file"),
 			action_name(opts));
 	rollback_lock_file(&index_lock);
@@ -964,6 +990,9 @@ static int save_todo(struct todo_list *todo_list, struct replay_opts *opts)
 	const char *todo_path = get_todo_path(opts);
 	int next = todo_list->current, offset, fd;
 
+	if (IS_REBASE_I())
+		next++;
+
 	fd = hold_lock_file_for_update(&todo_lock, todo_path, LOCK_DIE_ON_ERROR);
 	offset = next < todo_list->nr ?
 		todo_list->items[next].offset_in_buf : todo_list->buf.len;

sequencer.h

@@ -7,14 +7,16 @@ const char *git_path_seq_dir(void);
 
 enum replay_action {
 	REPLAY_REVERT,
-	REPLAY_PICK
+	REPLAY_PICK,
+	REPLAY_INTERACTIVE_REBASE
 };
 
 enum replay_subcommand {
 	REPLAY_NONE,
 	REPLAY_REMOVE_STATE,
 	REPLAY_CONTINUE,
-	REPLAY_ROLLBACK
+	REPLAY_ROLLBACK,
+	REPLAY_SKIP
 };
 
 struct replay_opts {