Re: [PATCH 4/4] odb: drop `alternates_db` field

On Tue, Aug 11, 2026 at 05:31:17PM -0500, Justin Tobler wrote:
> On 26/08/10 03:33PM, Patrick Steinhardt wrote:
> > The `struct object_database::alternates_db` field tracks the value of
> > the "GIT_ALTERNATE_OBJECT_DIRECTORIES" environment variable and is
> > used in `odb_prepare_alternates()`. It's not necessary to store it as a
> > separate field anymore though, as we stopped lazy-loading alternates.
> > Consequently, we can simply pass it to `odb_prepare_alternates()` via
> > `odb_new()` now.
> > 
> > Do so and remove the field.
> > 
> > Signed-off-by: Patrick Steinhardt <[email protected]>
> > ---
> [snip]
> > @@ -1126,7 +1126,7 @@ void odb_prepare(struct object_database *o, enum odb_prepare_flags flags)
> >  	 * the lifetime of the process.
> >  	 */
> >  	if (flags & ODB_PREPARE_FLUSH_CACHES) {
> > -		odb_prepare_alternates(o);
> > +		odb_prepare_alternates(o, NULL);
> >  		o->object_count_valid = 0;
> >  	}
> 
> Naive question: is the reason we don't need to wire the
> `GIT_ALTERNATE_OBJECT_DIRECTORIES` environment variable here because
> they have already been added as sources? IOW, when we invoke
> `odb_prepare_alternates()` after the initial set up, we only really care
> about re-reading the alternates file.

Yes, exactly. We set up alternates exactly once in `odb_new()`, and we
don't expect the environment variable to ever change in a running
process. And as `odb_prepare_alternates()` only adds but never removes
any it's fine to ignore those here.

I'll add a comment.

Patrick