Support for partial clones

[ThomasSowders]

Feature request: Add support for cloning and using repositories with the partial clone feature.

[olsen232]

#5776 has been closed since it is superceded by #5993 (and follow-ups)

[olsen232]

My current plan -

1. New error code EMISSING for when objects are referenced by the ODB, but missing from the ODB. New GIT_EMISSING error #5993
2. Detect when packfiles are promisor packfiles - Implements .promisor packfile detection #5996
3. New error code EPROMISED - return it when an EMISSING occurs in a promisor-packfile (not yet done)

This will make it easier to work with partial clones, which is my focus right now (as opposed to creating partial clones)

[olsen232]

@ethomson just looking at recent commits, it seems like you are the best at making things happen in libgit2 - can you comment on if this is a reasonable plan, and maybe even find me a reviewer with the necessary permissions?

[ethomson]

@ethomson just looking at recent commits, it seems like you are the best at making things happen in libgit2 - can you comment on if this is a reasonable plan, and maybe even find me a reviewer with the necessary permissions?

👋 Hey @olsen232, sorry for the delay in getting back to you. This seems reasonable to me. I need to do a bit more research on partial clones but overall, I think that this seems like the right direction.

[erikmchut]

@olsen232 are you still working on some of the prerequisites for partial clones?

[olsen232]

Hi @erikmchut and @ethomson

am I still working on it? Not really - I have a fork of libgit2 that seems to do what I want it to for now. I think Edward got a bit put off by the ambiguity of the problem, or git's implementation, or of my approach - the way it works in Git means that asking "is object 30f94c... missing but promised?" is unanswerable in a reasonable amount of time in the general case, but asking "is object 30f94c at path foo/bar/baz missing but promised" is answerable. This kinda messes up the existing error codes paradigm a bit and nothing ever got merged to libgit2.

The PR that got stuck is here: #5993