On Tue, Jun 04, 2024 at 03:28:07PM +0000, Karthik Nayak wrote:

Patrick Steinhardt [off-list ref] writes:

quoted

+int repo_migrate_ref_storage_format(struct repository *repo,
+				    enum ref_storage_format format,
+				    unsigned int flags,
+				    struct strbuf *errbuf)
+{
+	struct ref_store *old_refs = NULL, *new_refs = NULL;
+	struct ref_transaction *transaction = NULL;
+	struct strbuf buf = STRBUF_INIT;
+	struct migration_data data;
+	size_t reflog_count = 0;
+	char *new_gitdir = NULL;
+	int did_migrate_refs = 0;
+	int ret;
+
+	old_refs = get_main_ref_store(repo);

Should we add a check to ensure the `old_refs->repo->ref_storage_format`
and `format` are different?

Hm, yeah. We do have that check in git-refs(1), but having it here as
well wouldn't hurt. As the patch series has been merged to `next`, I'll
leave this for a future iteration though. Probably the one where I
implement support for migrating reflogs.

quoted

+
+	/*
+	 * We do not have any interfaces that would allow us to write many
+	 * reflog entries. Once we have them we can remove this restriction.
+	 */
+	if (refs_for_each_reflog(old_refs, count_reflogs, &reflog_count) < 0) {
+		strbuf_addstr(errbuf, "cannot count reflogs");
+		ret = -1;
+		goto done;
+	}
+	if (reflog_count) {
+		strbuf_addstr(errbuf, "migrating reflogs is not supported yet");
+		ret = -1;
+		goto done;
+	}

Isn't this restrictive? It would be nice to perhaps say "git refs
migrate --ignore-reflogs", which could make it possible to not care
about reflogs. But maybe that can be part of a follow up.

Oh yeah, it is. In this case it would be possible to add a flag to
override this check, because the result would be that we simply discard
all reflogs altogether. But I don't think adding such a flag makes
sense, because I'd much rather want to remove the underlying restriction
itself and start handling the migration of reflogs.

quoted

+	/*
+	 * Worktrees complicate the migration because every worktree has a
+	 * separate ref storage. While it should be feasible to implement, this
+	 * is pushed out to a future iteration.
+	 *
+	 * TODO: we should really be passing the caller-provided repository to
+	 * `has_worktrees()`, but our worktree subsystem doesn't yet support
+	 * that.
+	 */
+	if (has_worktrees()) {
+		strbuf_addstr(errbuf, "migrating repositories with worktrees is not supported yet");
+		ret = -1;
+		goto done;
+	}
+

Same as above.

Allowing users to override this would leave them with broken worktree
refdbs, so I don't think we should add such a flag, either.

Patrick