feat: filters and partial cloning: initial support

[staehle]

Resolves #1046

Hi @Byron! I'm Jake Staehle and I work at Roku here with @cesfahani. We've had an internal version of this for our internal tools for quite some time, but I recently updated our gitoxide version to 0.49 and had to refactor this code myself for all the changes since 0.40 -- I would very much rather not do that again, so it's upstreaming time :)

Introduce gix::remote::fetch::ObjectFilter (currently blob filters only) and plumb it through clone/fetch all the way into the fetch protocol, returning a clear error if the remote doesn’t advertise filter capability.

Also persist the partial-clone configuration on clone (remote.<name>.partialclonefilter, remote.<name>.promisor, extensions.partialclone) so the repository is marked as a promisor/partial clone in the same way as Git.

On the CLI/plumbing side, add --filter <spec> to gix clone, and allow fetch arguments to be either refspecs or raw object IDs (treated as additional wants).

Includes tests for filter parsing and for persisting partial-clone settings during clone, as well as a full round-trip test creating a blobless bare clone using gix, creating (using real git) a worktree from that, and then using gix verify that --filter=blob:none is working!

I did create a new repo https://github.com/staehle/gitoxide-testing for that last test to work properly, with a small set of known commits, tags, and blob objects. If you think this is useful, I'd be glad to transfer the repo to you / the GitoxideLabs group!

Let me know what you think! Thanks!

Credit:

• Original work by Cameron Esfahani cesfahani@roku.com
• Rewritten for modern Gitoxide by Jake Staehle jstaehle@roku.com

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[Copilot]

The condition is inverted. When additional_wants is empty, the code calls negotiate::add_wants() but then still iterates over additional_wants (lines 315-318), which does nothing. When additional_wants is NOT empty, it skips the normal wants logic and manually implements it (lines 323-350). This should be !self.additional_wants.is_empty() to properly handle the case when additional wants are present.

Suggested change

	if self.additional_wants.is_empty() {
	if !self.additional_wants.is_empty() {

[staehle]

It looks confusing so I get why copilot doesn't understand, but the condition is not inverted, and the behavior matches the surrounding design.

When additional_wants is empty, add_wants() delegates to negotiate::add_wants and then iterates self.additional_wants (which is empty), so that loop is a harmless no-op. This is the "normal fetch" path.

When additional_wants is non-empty, the code intentionally avoids negotiate::add_wants and instead builds the wants list itself (including want_ref() when supported) and then appends the additional object-id wants. This aligns with the other deliberate behavior you already saw:

• mark_complete_and_common_ref() forces MustNegotiate when additional wants exist.
• one_round() returns an "empty round" and intentionally skips have exchange/negotiation rounds since we want to ask for these objects directly.

So, flipping the condition to !self.additional_wants.is_empty() would make the non-empty case call negotiate::add_wants and then fall through into the manual wants logic, which would duplicate/alter behavior and be wrong.

[Copilot]

The filter is being suppressed when additional_wants is present (line 105). This means users cannot use object filters when fetching specific objects by ID. Unless there's a technical limitation preventing filters with additional wants, this restriction should be removed or clearly documented why filters and additional wants are mutually exclusive.

Suggested change

	.map(crate::remote::fetch::ObjectFilter::to_argument_string)
	.filter(|_| self.additional_wants.is_empty());
	.map(crate::remote::fetch::ObjectFilter::to_argument_string);

[staehle]

Hard disagree. This is intentional -- additional_wants SHOULD ignore blob filters, since if you specifically want to checkout a commit, you NEED those blobs.