tracking repository reference in commit object

Dear,

The lifetime of objects should be synchronized to prevent them from being GC'd; as is done with %submodule-owners in (git submodule). For an example, see Guix 41425#10.

(use-modules (guix git) (guix channels) (guix tests git) (git))
(define dir (url-cache-directory (channel-url (car %default-channels))))

(define repo (repository-open dir))

(define merge (find-commit repo "Merge"))
(define left (car (commit-parents merge)))

merge
;; $1 = #<git-commit b4440de133401abc6ce8be6c1c2e720efd9b2ba3>
left
;; $2 = #<git-commit 141262f266ab702c856f634889d4130ae661e79f>

(commit-relation left merge)
;; $3 = ancestor

(define repo 42)
(commit-relation left merge)
;; $4 = ancestor

(gc)
(commit-relation left merge)
Segmentation fault