From: Daniel Barkalow <barkalow@iabervon.org>

Helpers may use a line like "? name unchanged" to specify that there
is nothing new at that name, without any git-specific code to
determine the correct response.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
---

	Unchanged.

 Documentation/git-remote-helpers.txt |    4 +++-
 transport-helper.c                   |   22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletions(-)

diff --git a/Documentation/git-remote-helpers.txt b/Documentation/git-remote-helpers.txt
index d6c5268..f4b6a5a 100644
--- a/Documentation/git-remote-helpers.txt
+++ b/Documentation/git-remote-helpers.txt
@@ -84,7 +84,9 @@ CAPABILITIES
 REF LIST ATTRIBUTES
 -------------------
 
-None are defined yet, but the caller must accept any which are supplied.
+'unchanged'::
+	This ref is unchanged since the last import or fetch, although
+	the helper cannot necessarily determine what value that produced.
 
 Documentation
 -------------
diff --git a/transport-helper.c b/transport-helper.c
index 628a5ca..c87530e 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -206,6 +206,22 @@ static int fetch(struct transport *transport,
 	return -1;
 }
 
+static int has_attribute(const char *attrs, const char *attr) {
+	int len;
+	if (!attrs)
+		return 0;
+
+	len = strlen(attr);
+	for (;;) {
+		const char *space = strchrnul(attrs, ' ');
+		if (len == space - attrs && !strncmp(attrs, attr, len))
+			return 1;
+		if (!*space)
+			return 0;
+		attrs = space + 1;
+	}
+}
+
 static struct ref *get_refs_list(struct transport *transport, int for_push)
 {
 	struct child_process *helper;
@@ -240,6 +256,12 @@ static struct ref *get_refs_list(struct transport *transport, int for_push)
 			(*tail)->symref = xstrdup(buf.buf + 1);
 		else if (buf.buf[0] != '?')
 			get_sha1_hex(buf.buf, (*tail)->old_sha1);
+		if (eon) {
+			if (has_attribute(eon + 1, "unchanged")) {
+				(*tail)->status |= REF_STATUS_UPTODATE;
+				read_ref((*tail)->name, (*tail)->old_sha1);
+			}
+		}
 		tail = &((*tail)->next);
 	}
 	strbuf_release(&buf);
-- 
1.6.5.3.164.g07b0c

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