replace: introduce --convert-graft-file

This option is intended to help with the transition away from the
now-deprecated graft file.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-replace.txt

@@ -11,6 +11,7 @@ SYNOPSIS
 'git replace' [-f] <object> <replacement>
 'git replace' [-f] --edit <object>
 'git replace' [-f] --graft <commit> [<parent>...]
+'git replace' [-f] --convert-graft-file
 'git replace' -d <object>...
 'git replace' [--format=<format>] [-l [<pattern>]]
 
@@ -87,9 +88,13 @@ OPTIONS
 	content as <commit> except that its parents will be
 	[<parent>...] instead of <commit>'s parents. A replacement ref
 	is then created to replace <commit> with the newly created
-	commit. See contrib/convert-grafts-to-replace-refs.sh for an
-	example script based on this option that can convert grafts to
-	replace refs.
+	commit. Use `--convert-graft-file` to convert a
+	`$GIT_DIR/info/grafts` file and use replace refs instead.
+
+--convert-graft-file::
+	Creates graft commits for all entries in `$GIT_DIR/info/grafts`
+	and deletes that file upon success. The purpose is to help users
+	with transitioning off of the now-deprecated graft file.
 
 -l <pattern>::
 --list <pattern>::

builtin/replace.c

@@ -20,6 +20,7 @@ static const char * const git_replace_usage[] = {
 	N_("git replace [-f] <object> <replacement>"),
 	N_("git replace [-f] --edit <object>"),
 	N_("git replace [-f] --graft <commit> [<parent>...]"),
+	N_("git replace [-f] --convert-graft-file"),
 	N_("git replace -d <object>..."),
 	N_("git replace [--format=<format>] [-l [<pattern>]]"),
 	NULL
@@ -481,6 +482,38 @@ static int create_graft(int argc, const char **argv, int force, int gentle)
 	return replace_object_oid(old_ref, &old_oid, "replacement", &new_oid, force);
 }
 
+static int convert_graft_file(int force)
+{
+	const char *graft_file = get_graft_file();
+	FILE *fp = fopen_or_warn(graft_file, "r");
+	struct strbuf buf = STRBUF_INIT, err = STRBUF_INIT;
+	struct argv_array args = ARGV_ARRAY_INIT;
+
+	if (!fp)
+		return -1;
+
+	while (strbuf_getline(&buf, fp) != EOF) {
+		if (*buf.buf == '#')
+			continue;
+
+		argv_array_split(&args, buf.buf);
+		if (args.argc && create_graft(args.argc, args.argv, force, 1))
+			strbuf_addf(&err, "\n\t%s", buf.buf);
+		argv_array_clear(&args);
+	}
+	fclose(fp);
+
+	strbuf_release(&buf);
+
+	if (!err.len)
+		return unlink_or_warn(graft_file);
+
+	warning(_("could not convert the following graft(s):\n%s"), err.buf);
+	strbuf_release(&err);
+
+	return -1;
+}
+
 int cmd_replace(int argc, const char **argv, const char *prefix)
 {
 	int force = 0;
@@ -492,6 +525,7 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 		MODE_DELETE,
 		MODE_EDIT,
 		MODE_GRAFT,
+		MODE_CONVERT_GRAFT_FILE,
 		MODE_REPLACE
 	} cmdmode = MODE_UNSPECIFIED;
 	struct option options[] = {
@@ -499,6 +533,7 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 		OPT_CMDMODE('d', "delete", &cmdmode, N_("delete replace refs"), MODE_DELETE),
 		OPT_CMDMODE('e', "edit", &cmdmode, N_("edit existing object"), MODE_EDIT),
 		OPT_CMDMODE('g', "graft", &cmdmode, N_("change a commit's parents"), MODE_GRAFT),
+		OPT_CMDMODE(0, "convert-graft-file", &cmdmode, N_("convert existing graft file"), MODE_CONVERT_GRAFT_FILE),
 		OPT_BOOL_F('f', "force", &force, N_("replace the ref if it exists"),
 			   PARSE_OPT_NOCOMPLETE),
 		OPT_BOOL(0, "raw", &raw, N_("do not pretty-print contents for --edit")),
@@ -521,7 +556,8 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 	if (force &&
 	    cmdmode != MODE_REPLACE &&
 	    cmdmode != MODE_EDIT &&
-	    cmdmode != MODE_GRAFT)
+	    cmdmode != MODE_GRAFT &&
+	    cmdmode != MODE_CONVERT_GRAFT_FILE)
 		usage_msg_opt("-f only makes sense when writing a replacement",
 			      git_replace_usage, options);
 
@@ -554,6 +590,12 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 				      git_replace_usage, options);
 		return create_graft(argc, argv, force, 0);
 
+	case MODE_CONVERT_GRAFT_FILE:
+		if (argc != 0)
+			usage_msg_opt("--convert-graft-file takes no argument",
+				      git_replace_usage, options);
+		return !!convert_graft_file(force);
+
 	case MODE_LIST:
 		if (argc > 1)
 			usage_msg_opt("only one pattern can be given with -l",