[RFC/PATCH 2/9] ref-filter: implement '--points-at' option

[Karthik Nayak <karthik.188@gmail.com>]

In 'tag -l' we have '--points-at' option which lets users
list only tags which point to a particular commit, Implement
this option in 'ref-filter.{c,h}' so that the other commands
can benefit from this.

Based-on-patch-by: Jeff King <peff@peff.net>
Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 ref-filter.c | 26 ++++++++++++++++++++++++++
 ref-filter.h |  1 +
 2 files changed, 27 insertions(+)

diff --git a/ref-filter.c b/ref-filter.c
index 745d3b3..456b0fa 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -841,6 +841,29 @@ static int match_name_as_path(const char **pattern, const char *refname)
 	return 0;
 }
 
+/*
+ * Given a ref (sha1, refname) see if it points to a one of the sha1s
+ * in a sha1_array.
+ */
+static int match_points_at(struct sha1_array *points_at, const unsigned char *sha1,
+			   const char *refname)
+{
+	struct object *obj;
+
+	if (!points_at || !points_at->nr)
+		return 1;
+
+	if (sha1_array_lookup(points_at, sha1) >= 0)
+		return 1;
+
+	obj = parse_object_or_die(sha1, refname);
+	if (obj->type == OBJ_TAG &&
+	    sha1_array_lookup(points_at, ((struct tag *)obj)->tagged->sha1) >= 0)
+		return 1;
+
+	return 0;
+}
+
 /* Allocate space for a new ref_array_item and copy the objectname and flag to it */
 static struct ref_array_item *new_ref_array_item(const char *refname,
 						 const unsigned char *objectname,
@@ -874,6 +897,9 @@ int ref_filter_handler(const char *refname, const struct object_id *oid, int fla
 	if (*filter->name_patterns && !match_name_as_path(filter->name_patterns, refname))
 		return 0;
 
+	if (!match_points_at(&filter->points_at, oid->hash, refname))
+		return 0;
+
 	/*
 	 * We do not open the object yet; sort may only need refname
 	 * to do its job and the resulting list may yet to be pruned
diff --git a/ref-filter.h b/ref-filter.h
index 041a39a..a8980e7 100644
--- a/ref-filter.h
+++ b/ref-filter.h
@@ -39,6 +39,7 @@ struct ref_array {
 
 struct ref_filter {
 	const char **name_patterns;
+	struct sha1_array points_at;
 };
 
 struct ref_filter_cbdata {
-- 
2.4.2