MIDX woes, was Re: [ANNOUNCE] Git v2.54.0-rc2

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Junio,

On Tue, 14 Apr 2026, Junio C Hamano wrote:

>  * Further work on incremental repacking using MIDX/bitmap

I just noticed that a fetch with v2.54.0-rc2 into an existing repository
rendered it unusable for Git v2.53.0:

  fatal: multi-pack-index version 2 not recognized

Is it possible that v2.54.0-rc2 forcefully uses a MIDX version that has
_just_ been introduced?

If so, that might have been a premature bump of the default MIDX version,
if even the preceding Git version fails to handle that MIDX version. It is
guaranteed to cause substantial problems in setups where e.g. libgit2 or
JGit is expected to be used interchangeably with Git. It also causes
problems when users have to downgrade Git, or use several Git versions
side by side (e.g. using GitHub Desktop, which bundles its own version of
Git).

Ciao,
Johannes