Merge branch 'ag/sequencer-reduce-rewriting-todo'

The scripted version of "git rebase -i" wrote and rewrote the todo
list many times during a single step of its operation, and the
recent C-rewrite made a faithful conversion of the logic to C.  The
implementation has been updated to carry necessary information
around in-core to avoid rewriting the same file over and over
unnecessarily.

* ag/sequencer-reduce-rewriting-todo:
  rebase--interactive: move transform_todo_file()
  sequencer: use edit_todo_list() in complete_action()
  rebase-interactive: rewrite edit_todo_list() to handle the initial edit
  rebase-interactive: append_todo_help() changes
  rebase-interactive: use todo_list_write_to_file() in edit_todo_list()
  sequencer: refactor skip_unnecessary_picks() to work on a todo_list
  rebase--interactive: move rearrange_squash_in_todo_file()
  rebase--interactive: move sequencer_add_exec_commands()
  sequencer: change complete_action() to use the refactored functions
  sequencer: make sequencer_make_script() write its script to a strbuf
  sequencer: refactor rearrange_squash() to work on a todo_list
  sequencer: refactor sequencer_add_exec_commands() to work on a todo_list
  sequencer: refactor check_todo_list() to work on a todo_list
  sequencer: introduce todo_list_write_to_file()
  sequencer: refactor transform_todos() to work on a todo_list
  sequencer: remove the 'arg' field from todo_item
  sequencer: make the todo_list structure public
  sequencer: changes in parse_insn_buffer()

sequencer.h

@@ -10,6 +10,7 @@ struct repository;
 const char *git_path_commit_editmsg(void);
 const char *git_path_seq_dir(void);
 const char *rebase_path_todo(void);
+const char *rebase_path_todo_backup(void);
 
 #define APPEND_SIGNOFF_DEDUP (1u << 0)
 
@@ -66,14 +67,60 @@ struct replay_opts {
 };
 #define REPLAY_OPTS_INIT { .action = -1, .current_fixups = STRBUF_INIT }
 
-enum missing_commit_check_level {
-	MISSING_COMMIT_CHECK_IGNORE = 0,
-	MISSING_COMMIT_CHECK_WARN,
-	MISSING_COMMIT_CHECK_ERROR
+/*
+ * Note that ordering matters in this enum. Not only must it match the mapping
+ * of todo_command_info (in sequencer.c), it is also divided into several
+ * sections that matter.  When adding new commands, make sure you add it in the
+ * right section.
+ */
+enum todo_command {
+	/* commands that handle commits */
+	TODO_PICK = 0,
+	TODO_REVERT,
+	TODO_EDIT,
+	TODO_REWORD,
+	TODO_FIXUP,
+	TODO_SQUASH,
+	/* commands that do something else than handling a single commit */
+	TODO_EXEC,
+	TODO_BREAK,
+	TODO_LABEL,
+	TODO_RESET,
+	TODO_MERGE,
+	/* commands that do nothing but are counted for reporting progress */
+	TODO_NOOP,
+	TODO_DROP,
+	/* comments (not counted for reporting progress) */
+	TODO_COMMENT
 };
 
-int write_message(const void *buf, size_t len, const char *filename,
-		  int append_eol);
+struct todo_item {
+	enum todo_command command;
+	struct commit *commit;
+	unsigned int flags;
+	int arg_len;
+	/* The offset of the command and its argument in the strbuf */
+	size_t offset_in_buf, arg_offset;
+};
+
+struct todo_list {
+	struct strbuf buf;
+	struct todo_item *items;
+	int nr, alloc, current;
+	int done_nr, total_nr;
+	struct stat_data stat;
+};
+
+#define TODO_LIST_INIT { STRBUF_INIT }
+
+int todo_list_parse_insn_buffer(struct repository *r, char *buf,
+				struct todo_list *todo_list);
+int todo_list_write_to_file(struct repository *r, struct todo_list *todo_list,
+			    const char *file, const char *shortrevisions,
+			    const char *shortonto, int num, unsigned flags);
+void todo_list_release(struct todo_list *todo_list);
+const char *todo_item_get_arg(struct todo_list *todo_list,
+			      struct todo_item *item);
 
 /* Call this to setup defaults before parsing command line options */
 void sequencer_init_config(struct replay_opts *opts);
@@ -93,19 +140,19 @@ int sequencer_remove_state(struct replay_opts *opts);
  * commits should be rebased onto the new base, this flag needs to be passed.
  */
 #define TODO_LIST_REBASE_COUSINS (1U << 4)
-int sequencer_make_script(struct repository *repo, FILE *out,
-			  int argc, const char **argv,
-			  unsigned flags);
+#define TODO_LIST_APPEND_TODO_HELP (1U << 5)
 
-int sequencer_add_exec_commands(struct repository *r, const char *command);
-int transform_todos(struct repository *r, unsigned flags);
-enum missing_commit_check_level get_missing_commit_check_level(void);
-int check_todo_list(struct repository *r);
+int sequencer_make_script(struct repository *r, struct strbuf *out, int argc,
+			  const char **argv, unsigned flags);
+
+void todo_list_add_exec_commands(struct todo_list *todo_list,
+				 struct string_list *commands);
+int check_todo_list_from_file(struct repository *r);
 int complete_action(struct repository *r, struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
-		    const char *onto, const char *orig_head, const char *cmd,
-		    unsigned autosquash);
-int rearrange_squash(struct repository *r);
+		    const char *onto, const char *orig_head, struct string_list *commands,
+		    unsigned autosquash, struct todo_list *todo_list);
+int todo_list_rearrange_squash(struct todo_list *todo_list);
 
 /*
  * Append a signoff to the commit message in "msgbuf". The ignore_footer