Re: [PATCH 01/20] pack-revindex: introduce a new API

On Tue, Jan 12, 2021 at 03:41:28AM -0500, Jeff King wrote:

quoted

+int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos)
+{
+	int ret;
+
+	if (load_pack_revindex(p) < 0)
+		return -1;

This one lazy-loads the revindex for us, which seems handy...

quoted

+uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos)
+{
+	if (!p->revindex)
+		BUG("pack_pos_to_index: reverse index not yet loaded");
+	if (pos >= p->num_objects)
+		BUG("pack_pos_to_index: out-of-bounds object at %"PRIu32, pos);
+	return p->revindex[pos].nr;
+}

But these ones don't. I'm glad we at least catch it with a BUG(), but it
makes the API a little funny. Returning an error here would require a
similarly awkward out-parameter, I guess.

Having now looked at the callers through the series, I think adding an
error return to pack_pos_to_index() would be really awkward (since it
cannot currently fail).

We _could_ insist that callers of offset_to_pack_pos() also make sure
the revindex is loaded themselves. But it would be annoying and
error-prone to check the existing callers. So I'm OK with leaving this
asymmetry in the API.

-Peff