Re: [PATCH v3 1/3] midx: teach "git multi-pack-index repack" honor "git repack" configurations

> "Son Luong Ngoc via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
> > From: Son Luong Ngoc <sluongng@gmail.com>
> >
> > Previously, when the "repack" subcommand of "git multi-pack-index" command
> > creates new packfile(s), it does not call the "git repack" command but
> > instead directly calls the "git pack-objects" command, and the
> > configuration variables meant for the "git repack" command, like
> > "repack.usedaeltabaseoffset", are ignored.
> 
> When we talk about the current state of the code (i.e. before
> applying this patch), we do not say "previously".  It's not like you
> are complaining about a recent breakage, e.g. "previously X worked
> like this but since change Y, it instead works like that, which
> breaks Z".
> 
> > This patch ensured "git multi-pack-index" checks the configuration
> > variables used by "git repack" and passes the corresponding options to
> > the underlying "git pack-objects" command.
> 
> We write this part in imperative mood, as if we are giving an order
> to the codebase to "become like so".  We do not give an observation
> about the patch or the author ("This patch does X, this patch also
> does Y", "I do X, I do Y").
> 
> Taking these two together, perhaps like:
> 
>     When the "repack" subcommand of "git multi-pack-index" command
>     creates new packfile(s), it does not call the "git repack"
>     command but instead directly calls the "git pack-objects"
>     command, and the configuration variables meant for the "git
>     repack" command, like "repack.usedaeltabaseoffset", are ignored.
> 
>     Check the configuration variables used by "git repack" ourselves
>     in "git multi-index-pack" and pass the corresponding options to
>     underlying "git pack-objects".

> 
> > Note that `repack.writeBitmaps` configuration is ignored, as the
> > pack bitmap facility is useful only with a single packfile.
> 
> Good.
> 
> > +	int delta_base_offset = 1;
> > +	int use_delta_islands = 0;
> 
> These give the default values for two configurations and over there
> builtin/repack.c has these lines:
> 
>     17	static int delta_base_offset = 1;
>     18	static int pack_kept_objects = -1;
>     19	static int write_bitmaps = -1;
>     20	static int use_delta_islands;
>     21	static char *packdir, *packtmp;
> 
> When somebody is tempted to update these to change the default used
> by "git repack", it should be easy to notice that such a change must
> be accompanied by a matching change to the lines you are introducing
> in this patch, or we'll be out of sync.
> 
> The easiest way to avoid such a problem may be to stop bypassing
> "git repack" and calling "pack-objects" ourselves.  That is the
> reason why the configuration variables honored by "git repack" are
> ignored in this codepath in the first place.  But that is not the
> approach we are taking, so we need a reasonable way to tell those
> who update this file and builtin/repack.c to make matching changes.
> At the very least, perhaps we should give a comment above these two
> lines in this file, e.g.
> 
> 	/*
> 	 * when updating the default for these configuration
> 	 * variables in builtin/repack.c, these must be adjusted
> 	 * to match.
> 	 */
> 	int delta_base_offset = 1;
> 	int use_delta_islands = 0;
> 
> or something like that.