Re: [PATCH v2 8/9] object-store: remove global array of cached objects

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 11, 2025, 22:58 UTC
Message-ID: <xmqqtt6ul30k.fsf@gitster.g>
In-Reply-To: <20250411-pks-split-object-file-v2-8-2bea0c9033ae@pks.im>

Patrick Steinhardt <ps@pks.im> writes:

Show 7 quoted lines

> Cached objects are virtual objects that can be set up without writing
> anything into the object store directly. This mechanism for example
> allows us to create fake commits in git-blame(1).
>
> The cached objects are stored in a global variable. Refactor the code so
> that we instead store the array as part of the raw object store. This is
> another step into the direction of libifying our object database.

While we do need some execution context object to hang these virtual objects, once we decide that it cannot be global, I am not sure if epository objects are good home for them. If your application running in a repository needs to give one object name to a virtual object, and then that same application wants to access a submodule of that repository in the same process image, wouldn't you have one in-core repository object for the top-level superproject, and one for each submodule? If a submodule commit bound to a path in the superproject's tree is a viertual "pretend" commit object or if it has a virtual "pretend" tree object, don't you need to expose these to both submodule and superproject repositories, if your application wants to seamlessly cross the module boundary (think "git grep --recurse-submodules" or something)?

For now, as long as the_repository is being used as that "execution context object", and not a repository instance passed along the call chain, then the globalness of these virtual objects is maintained, so this change will not cause breakage (e.g., such an application may want to pick up the virtual object from the repository instance for the superproject and it may find it, but when traversing down to a submdoule, the same virtual object may not be found in the repository instance for the submodule it descended into and working in, if you make it per repository and pass repository instance around along the call chain). But eventually somebody will start saying "let's remove USE_THE_REPOSITORY_VARIABLE", at which point I am not sure how subtle such a bug would become.