sequencer: refactor skip_unnecessary_picks() to work on a todo_list

This refactors skip_unnecessary_picks() to work on a todo_list.  As this
function is only called by complete_action() (and thus is not used by
rebase -p), the file-handling logic is completely dropped here.

Instead of truncating the todo list’s buffer, the items are moved to
the beginning of the list, eliminating the need to reparse the list.
This also means its buffer cannot be directly written to the disk.

rewrite_file() is then removed, as it is now unused.

Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -4700,52 +4700,22 @@ out:
 	return res;
 }
 
-static int rewrite_file(const char *path, const char *buf, size_t len)
-{
-	int rc = 0;
-	int fd = open(path, O_WRONLY | O_TRUNC);
-	if (fd < 0)
-		return error_errno(_("could not open '%s' for writing"), path);
-	if (write_in_full(fd, buf, len) < 0)
-		rc = error_errno(_("could not write to '%s'"), path);
-	if (close(fd) && !rc)
-		rc = error_errno(_("could not close '%s'"), path);
-	return rc;
-}
-
 /* skip picking commits whose parents are unchanged */
-static int skip_unnecessary_picks(struct repository *r, struct object_id *output_oid)
+static int skip_unnecessary_picks(struct repository *r,
+				  struct todo_list *todo_list,
+				  struct object_id *base_oid)
 {
-	const char *todo_file = rebase_path_todo();
-	struct strbuf buf = STRBUF_INIT;
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct object_id *parent_oid;
-	int fd, i;
+	int i;
 
-	if (!read_oneliner(&buf, rebase_path_onto(), 0))
-		return error(_("could not read 'onto'"));
-	if (get_oid(buf.buf, output_oid)) {
-		strbuf_release(&buf);
-		return error(_("need a HEAD to fixup"));
-	}
-	strbuf_release(&buf);
-
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
-		return -1;
-	if (todo_list_parse_insn_buffer(r, todo_list.buf.buf, &todo_list) < 0) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
-
-	for (i = 0; i < todo_list.nr; i++) {
-		struct todo_item *item = todo_list.items + i;
+	for (i = 0; i < todo_list->nr; i++) {
+		struct todo_item *item = todo_list->items + i;
 
 		if (item->command >= TODO_NOOP)
 			continue;
 		if (item->command != TODO_PICK)
 			break;
 		if (parse_commit(item->commit)) {
-			todo_list_release(&todo_list);
 			return error(_("could not parse commit '%s'"),
 				oid_to_hex(&item->commit->object.oid));
 		}
@@ -4754,42 +4724,26 @@ static int skip_unnecessary_picks(struct repository *r, struct object_id *output
 		if (item->commit->parents->next)
 			break; /* merge commit */
 		parent_oid = &item->commit->parents->item->object.oid;
-		if (!oideq(parent_oid, output_oid))
+		if (!oideq(parent_oid, base_oid))
 			break;
-		oidcpy(output_oid, &item->commit->object.oid);
+		oidcpy(base_oid, &item->commit->object.oid);
 	}
 	if (i > 0) {
-		int offset = get_item_line_offset(&todo_list, i);
 		const char *done_path = rebase_path_done();
 
-		fd = open(done_path, O_CREAT | O_WRONLY | O_APPEND, 0666);
-		if (fd < 0) {
-			error_errno(_("could not open '%s' for writing"),
-				    done_path);
-			todo_list_release(&todo_list);
-			return -1;
-		}
-		if (write_in_full(fd, todo_list.buf.buf, offset) < 0) {
+		if (todo_list_write_to_file(r, todo_list, done_path, NULL, NULL, i, 0)) {
 			error_errno(_("could not write to '%s'"), done_path);
-			todo_list_release(&todo_list);
-			close(fd);
-			return -1;
-		}
-		close(fd);
-
-		if (rewrite_file(rebase_path_todo(), todo_list.buf.buf + offset,
-				 todo_list.buf.len - offset) < 0) {
-			todo_list_release(&todo_list);
 			return -1;
 		}
 
-		todo_list.current = i;
-		if (is_fixup(peek_command(&todo_list, 0)))
-			record_in_rewritten(output_oid, peek_command(&todo_list, 0));
+		MOVE_ARRAY(todo_list->items, todo_list->items + i, todo_list->nr - i);
+		todo_list->nr -= i;
+		todo_list->current = 0;
+
+		if (is_fixup(peek_command(todo_list, 0)))
+			record_in_rewritten(base_oid, peek_command(todo_list, 0));
 	}
 
-	todo_list_release(&todo_list);
-
 	return 0;
 }
 
@@ -4860,6 +4814,11 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 		return -1;
 	}
 
+	if (opts->allow_ff && skip_unnecessary_picks(r, &new_todo, &oid)) {
+		todo_list_release(&new_todo);
+		return error(_("could not skip unnecessary pick commands"));
+	}
+
 	if (todo_list_write_to_file(r, &new_todo, todo_file, NULL, NULL, -1,
 				    flags & ~(TODO_LIST_SHORTEN_IDS))) {
 		todo_list_release(&new_todo);
@@ -4868,9 +4827,6 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 
 	todo_list_release(&new_todo);
 
-	if (opts->allow_ff && skip_unnecessary_picks(r, &oid))
-		return error(_("could not skip unnecessary pick commands"));
-
 	if (checkout_onto(opts, onto_name, oid_to_hex(&oid), orig_head))
 		return -1;