merge-tree: support multiple batched merges with --stdin

Add an option, --stdin, to merge-tree which will accept lines of input
with two branches to merge per line, and which will perform all the
merges and give output for each in turn.  This option implies -z, and
modifies the output to also include a merge status since the exit code
of the program can no longer convey that information now that multiple
merges are involved.

This could be useful, for example, by Git hosting providers.  When one
branch is updated, one may want to check whether all code reviews
targetting that branch can still cleanly merge.  Avoiding the overhead
of starting up a separate process for each of those code reviews might
provide significant savings in a repository with many code reviews.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 39 insertions, 3 deletions

diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index ae5782917b..fe853aa8f9 100644
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -402,6 +402,7 @@ struct merge_tree_options {
 	int allow_unrelated_histories;
 	int show_messages;
 	int name_only;
+	int use_stdin;
 };
 
 static int real_merge(struct merge_tree_options *o,
@@ -412,6 +413,7 @@ static int real_merge(struct merge_tree_options *o,
 	struct commit_list *merge_bases = NULL;
 	struct merge_options opt;
 	struct merge_result result = { 0 };
+	int show_messages = o->show_messages;
 
 	parent1 = get_merge_parent(branch1);
 	if (!parent1)
@@ -443,9 +445,11 @@ static int real_merge(struct merge_tree_options *o,
 	if (result.clean < 0)
 		die(_("failure to merge"));
 
-	if (o->show_messages == -1)
-		o->show_messages = !result.clean;
+	if (show_messages == -1)
+		show_messages = !result.clean;
 
+	if (o->use_stdin)
+		printf("%d%c", result.clean, line_termination);
 	printf("%s%c", oid_to_hex(&result.tree->object.oid), line_termination);
 	if (!result.clean) {
 		struct string_list conflicted_files = STRING_LIST_INIT_NODUP;
@@ -467,11 +471,13 @@ static int real_merge(struct merge_tree_options *o,
 		}
 		string_list_clear(&conflicted_files, 1);
 	}
-	if (o->show_messages) {
+	if (show_messages) {
 		putchar(line_termination);
 		merge_display_update_messages(&opt, line_termination == '\0',
 					      &result);
 	}
+	if (o->use_stdin)
+		putchar(line_termination);
 	merge_finalize(&opt, &result);
 	return !result.clean; /* result.clean < 0 handled above */
 }
@@ -505,6 +511,10 @@ int cmd_merge_tree(int argc, const char **argv, const char *prefix)
 			   &o.allow_unrelated_histories,
 			   N_("allow merging unrelated histories"),
 			   PARSE_OPT_NONEG),
+		OPT_BOOL_F(0, "stdin",
+			   &o.use_stdin,
+			   N_("perform multiple merges, one per line of input"),
+			   PARSE_OPT_NONEG),
 		OPT_END()
 	};
 
@@ -512,6 +522,32 @@ int cmd_merge_tree(int argc, const char **argv, const char *prefix)
 	original_argc = argc - 1; /* ignoring argv[0] */
 	argc = parse_options(argc, argv, prefix, mt_options,
 			     merge_tree_usage, PARSE_OPT_STOP_AT_NON_OPTION);
+
+	/* Handle --stdin */
+	if (o.use_stdin) {
+		struct strbuf buf = STRBUF_INIT;
+
+		if (o.mode == MODE_TRIVIAL)
+			die(_("--trivial-merge is incompatible with all other options"));
+		line_termination = '\0';
+		while (strbuf_getline_lf(&buf, stdin) != EOF) {
+			struct strbuf **split;
+			int result;
+
+			split = strbuf_split(&buf, ' ');
+			if (!split[0] || !split[1] || split[2])
+				die(_("malformed input line: '%s'."), buf.buf);
+			strbuf_rtrim(split[0]);
+			result = real_merge(&o, split[0]->buf, split[1]->buf, prefix);
+			if (result < 0)
+				die(_("merging cannot continue; got unclean result of %d"), result);
+			strbuf_list_free(split);
+		}
+		strbuf_release(&buf);
+		return 0;
+	}
+
+	/* Figure out which mode to use */
 	switch (o.mode) {
 	default:
 		BUG("unexpected command mode %d", o.mode);