[PATCH v3 04/16] sequencer: introduce todo_list_write_to_file()

[Alban Gruin <alban.gruin@gmail.com>]

This introduces a new function to recreate the text of a todo list from
its commands and write it to a file.  This will be useful as the next
few commits will change the use of the buffer in struct todo_list so it
will no longer be a mirror of the file on disk.

This functionality can already be found in todo_list_transform(), but it
is specifically made to replace the buffer of a todo list, which is not
the desired behaviour.  Thus, the part of todo_list_transform() that
actually creates the buffer is moved to a new function,
todo_list_to_strbuf().  The rest is unused, and so is dropped.

todo_list_write_to_file() can also take care of appending the help text
to the buffer before writing it to the disk, or to write only the first
n items of the list.  This feature will be used by
skip_unnecessary_picks(), which has to write done commands in a file.

Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
---
 sequencer.c | 60 ++++++++++++++++++++++++++++++++++++-----------------
 sequencer.h |  6 +++++-
 2 files changed, 46 insertions(+), 20 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index e1097660ed..19f24825d4 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4454,24 +4454,27 @@ int sequencer_add_exec_commands(const char *commands)
 	return i;
 }
 
-void todo_list_transform(struct todo_list *todo_list, unsigned flags)
+static void todo_list_to_strbuf(struct todo_list *todo_list, struct strbuf *buf,
+				int num, unsigned flags)
 {
-	struct strbuf buf = STRBUF_INIT;
 	struct todo_item *item;
-	int i;
+	int i, max = todo_list->nr;
 
-	for (item = todo_list->items, i = 0; i < todo_list->nr; i++, item++) {
+	if (num > 0 && num < max)
+		max = num;
+
+	for (item = todo_list->items, i = 0; i < max; i++, item++) {
 		/* if the item is not a command write it and continue */
 		if (item->command >= TODO_COMMENT) {
-			strbuf_addf(&buf, "%.*s\n", item->arg_len, item->arg);
+			strbuf_addf(buf, "%.*s\n", item->arg_len, item->arg);
 			continue;
 		}
 
 		/* add command to the buffer */
 		if (flags & TODO_LIST_ABBREVIATE_CMDS)
-			strbuf_addch(&buf, command_to_char(item->command));
+			strbuf_addch(buf, command_to_char(item->command));
 		else
-			strbuf_addstr(&buf, command_to_string(item->command));
+			strbuf_addstr(buf, command_to_string(item->command));
 
 		/* add commit id */
 		if (item->commit) {
@@ -4481,27 +4484,47 @@ void todo_list_transform(struct todo_list *todo_list, unsigned flags)
 
 			if (item->command == TODO_MERGE) {
 				if (item->flags & TODO_EDIT_MERGE_MSG)
-					strbuf_addstr(&buf, " -c");
+					strbuf_addstr(buf, " -c");
 				else
-					strbuf_addstr(&buf, " -C");
+					strbuf_addstr(buf, " -C");
 			}
 
-			strbuf_addf(&buf, " %s", oid);
+			strbuf_addf(buf, " %s", oid);
 		}
 
 		/* add all the rest */
 		if (!item->arg_len)
-			strbuf_addch(&buf, '\n');
+			strbuf_addch(buf, '\n');
 		else
-			strbuf_addf(&buf, " %.*s\n", item->arg_len, item->arg);
+			strbuf_addf(buf, " %.*s\n", item->arg_len, item->arg);
 	}
+}
 
-	strbuf_reset(&todo_list->buf);
-	strbuf_add(&todo_list->buf, buf.buf, buf.len);
+int todo_list_write_to_file(struct todo_list *todo_list, const char *file,
+			    const char *shortrevisions, const char *shortonto,
+			    int num, unsigned flags)
+{
+	int edit_todo = !(shortrevisions && shortonto), res;
+	struct strbuf buf = STRBUF_INIT;
+
+	todo_list_to_strbuf(todo_list, &buf, num, flags);
+
+	if (flags & TODO_LIST_APPEND_TODO_HELP) {
+		int command_count = count_commands(todo_list);
+		if (!edit_todo) {
+			strbuf_addch(&buf, '\n');
+			strbuf_commented_addf(&buf, Q_("Rebase %s onto %s (%d command)",
+						       "Rebase %s onto %s (%d commands)",
+						       command_count),
+					      shortrevisions, shortonto, command_count);
+		}
+		append_todo_help(edit_todo, flags & TODO_LIST_KEEP_EMPTY, &buf);
+	}
+
+	res = write_message(buf.buf, buf.len, file, 0);
 	strbuf_release(&buf);
 
-	if (todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list))
-		BUG("unusable todo list");
+	return res;
 }
 
 int transform_todo_file(unsigned flags)
@@ -4518,9 +4541,8 @@ int transform_todo_file(unsigned flags)
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
 
-	todo_list_transform(&todo_list, flags);
-
-	res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
+	res = todo_list_write_to_file(&todo_list, todo_file,
+				      NULL, NULL, -1, flags);
 	todo_list_release(&todo_list);
 	return res;
 }
diff --git a/sequencer.h b/sequencer.h
index 708d042f0e..e69357c95b 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,7 +119,9 @@ struct todo_list {
 #define TODO_LIST_INIT { STRBUF_INIT }
 
 int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list);
-void todo_list_transform(struct todo_list *todo_list, unsigned flags);
+int todo_list_write_to_file(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);
 
 /* Call this to setup defaults before parsing command line options */
@@ -139,6 +141,8 @@ 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)
+#define TODO_LIST_APPEND_TODO_HELP (1U << 5)
+
 int sequencer_make_script(FILE *out, int argc, const char **argv,
 			  unsigned flags);
 
-- 
2.19.1.872.ga867da739e