1 files changed, 73 insertions, 0 deletions
diff --git a/replace-object.c b/replace-object.c
new file mode 100644
index 0000000000..801b5c1678
--- /dev/null
+++ b/replace-object.c
@@ -0,0 +1,73 @@
+#include "cache.h"
+#include "oidmap.h"
+#include "object-store.h"
+#include "replace-object.h"
+#include "refs.h"
+#include "repository.h"
+#include "commit.h"
+
+static int register_replace_ref(const char *refname,
+				const struct object_id *oid,
+				int flag, void *cb_data)
+{
+	/* Get sha1 from refname */
+	const char *slash = strrchr(refname, '/');
+	const char *hash = slash ? slash + 1 : refname;
+	struct replace_object *repl_obj = xmalloc(sizeof(*repl_obj));
+
+	if (get_oid_hex(hash, &repl_obj->original.oid)) {
+		free(repl_obj);
+		warning("bad replace ref name: %s", refname);
+		return 0;
+	}
+
+	/* Copy sha1 from the read ref */
+	oidcpy(&repl_obj->replacement, oid);
+
+	/* Register new object */
+	if (oidmap_put(the_repository->objects->replace_map, repl_obj))
+		die("duplicate replace ref: %s", refname);
+
+	return 0;
+}
+
+static void prepare_replace_object(struct repository *r)
+{
+	if (r->objects->replace_map)
+		return;
+
+	r->objects->replace_map =
+		xmalloc(sizeof(*r->objects->replace_map));
+	oidmap_init(r->objects->replace_map, 0);
+
+	for_each_replace_ref(r, register_replace_ref, NULL);
+}
+
+/* We allow "recursive" replacement. Only within reason, though */
+#define MAXREPLACEDEPTH 5
+
+/*
+ * If a replacement for object oid has been set up, return the
+ * replacement object's name (replaced recursively, if necessary).
+ * The return value is either oid or a pointer to a
+ * permanently-allocated value.  This function always respects replace
+ * references, regardless of the value of check_replace_refs.
+ */
+const struct object_id *do_lookup_replace_object(struct repository *r,
+						 const struct object_id *oid)
+{
+	int depth = MAXREPLACEDEPTH;
+	const struct object_id *cur = oid;
+
+	prepare_replace_object(r);
+
+	/* Try to recursively replace the object */
+	while (depth-- > 0) {
+		struct replace_object *repl_obj =
+			oidmap_get(r->objects->replace_map, cur);
+		if (!repl_obj)
+			return cur;
+		cur = &repl_obj->replacement;
+	}
+	die("replace depth too high for object %s", oid_to_hex(oid));
+}