+static int merging_a_throwaway_tag(struct commit *commit)
+{
+ char *tag_ref;
+ struct object_id oid;
+ int is_throwaway_tag = 0;
+
+ /* Are we merging a tag? */
+ if (!merge_remote_util(commit) ||
+ !merge_remote_util(commit)->obj ||
+ merge_remote_util(commit)->obj->type != OBJ_TAG)
+ return is_throwaway_tag;
+
+ /*
+ * Now we know we are merging a tag object. Are we downstream
+ * and following the tags from upstream? If so, we must have
+ * the tag object pointed at by "refs/tags/$T" where $T is the
+ * tagname recorded in the tag object. We want to allow such
+ * a "just to catch up" merge to fast-forward.
+ *
+ * Otherwise, we are playing an integrator's role, making a
+ * merge with a throw-away tag from a contributor with
+ * something like "git pull $contributor $signed_tag".
+ * We want to forbid such a merge from fast-forwarding
+ * by default; otherwise we would not keep the signature
+ * anywhere.
+ */
+ tag_ref = xstrfmt("refs/tags/%s",
+ ((struct tag *)merge_remote_util(commit)->obj)->tag);
+ if (!read_ref(tag_ref, &oid) &&
+ !oidcmp(&oid, &merge_remote_util(commit)->obj->oid))
+ is_throwaway_tag = 0;
+ else
+ is_throwaway_tag = 1;
+ free(tag_ref);
+ return is_throwaway_tag;
+}
+