Re: [PATCH 1/2] midx: fix `BUG()` when getting preferred pack without a reverse index

> On Tue, Dec 09, 2025 at 07:22:11PM -0500, Taylor Blau wrote:
> > On Mon, Dec 08, 2025 at 07:27:14PM +0100, Patrick Steinhardt wrote:
> > > The function `midx_preferred_pack()` returns the preferred pack for a
> > > given multi-pack index. To compute the preferred pack we:
> > >
> > >   1. Look up the position of the first object indexed by the multi-pack
> > >      index.
> > >
> > >   2. Convert this position from pseudo-pack order into MIDX order.
> > >
> > >   3. We then look up pack that corresponds to this MIDX index.
> >
> > I think the implementation of midx_preferred_pack() works a little bit
> > differently than is described here. I often get confused when working in
> > this area juggling between the various object/pack orderings in my head.
>
> Hm, I feel like I am missing something.
>
> > midx_preferred_pack() cares about converting from the first position in
> > pseudo-pack order back into MIDX object order. To do that, we convert
> > the pseudo-pack position into a MIDX one, and then lookup the pack that
> > represents that object.
>
> Isn't that what I say in (2) and (3)? Or is this about (1) being
> inaccurate? Would this sequence be more accurate:
>
>   1. Take the first position indexed by the MIDX in pseudo-pack order.
>
>   2. Convert this pseudo-pack position into the MIDX position.
>
>   3. We then look up the pack that corresponds to this MIDX position.
>
> In any case, I agree with you that juggling these different positions is
> quite something :)