decorate: clean up and document API

diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index b69f7d3be2bd4585a6233d0f8361c55a76ae0a5d..22034f87e7f8c7fa1166d3731319aca610fef2a2 100644 (file)
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c
@@ -571,7 +571,7 @@ static void find_merge_parents(struct merge_parents *result,
        head_commit = lookup_commit(head);
        if (head_commit)
                commit_list_insert(head_commit, &parents);
-       parents = reduce_heads(parents);
+       reduce_heads_replace(&parents);
 
        while (parents) {
                struct commit *cmit = pop_commit(&parents);