Re: [PATCH v4 00/16] Fix git-gc losing objects in multi worktree

[Michael J Gruber <git@grubix.eu>]

Nguyễn Thái Ngọc Duy venit, vidit, dixit 23.08.2017 14:36:
> "git gc" when used in multiple worktrees ignore some per-worktree
> references: object references in the index, HEAD and reflog. This
> series fixes it by making the revision walker include these from all
> worktrees by default (and the series is basically split in three parts
> in the same order). There's a couple more cleanups in refs.c. Luckily
> it does not conflict with anything in 'pu'.
> 
> Compared to v3 [1], the largest change is supporting multi worktree in
> the reflog iterator. The merge iterator is now used (Micheal was right
> all along).
> 
> [1] https://public-inbox.org/git/20170419110145.5086-1-pclouds@gmail.com/
> 
> Nguyễn Thái Ngọc Duy (16):
>   revision.h: new flag in struct rev_info wrt. worktree-related refs
>   refs.c: use is_dir_sep() in resolve_gitlink_ref()
>   revision.c: refactor add_index_objects_to_pending()
>   revision.c: --indexed-objects add objects from all worktrees
>   refs.c: refactor get_submodule_ref_store(), share common free block
>   refs: move submodule slash stripping code to get_submodule_ref_store
>   refs: add refs_head_ref()
>   revision.c: use refs_for_each*() instead of for_each_*_submodule()
>   refs.c: move for_each_remote_ref_submodule() to submodule.c
>   refs: remove dead for_each_*_submodule()
>   revision.c: --all adds HEAD from all worktrees
>   files-backend: make reflog iterator go through per-worktree reflog
>   revision.c: --reflog add HEAD reflog from all worktrees
>   rev-list: expose and document --single-worktree
>   refs.c: remove fallback-to-main-store code get_submodule_ref_store()
>   refs.c: reindent get_submodule_ref_store()

I probably won't be able to review this (many commits without commit
message), but I'm happy to see progress on the "--all" and prune front
(and will test). I suggest we think about the UI exposure a bit when it
comes to including all heads or naming options, though:

* HEAD is "the current head"
* refs/heads is where all local branch heads are

* --branches is the rev-list/log option for refs/heads/*
* --all is the rev-list/log option for refs/* plus HEAD
* HEAD is the rev-list/log argument for HEAD

* --heads is the show-ref option limiting to refs/heads/*
* --head is the show-ref option which adds HEAD

* refs/heads is the for-each-ref-pattern for refs/heads/*
* HEAD is not the for-each-ref-pattern for HEAD
[I'll suggest a patch to change the latter, shortly.]

I would hope that the result of this series and other efforts will be:

* consistent way to specify "all local branch heads"
* consistent way to specify "the head" aka HEAD
* consistent way to specify "all linked worktree heads"
[* maybe something for submodules...]

This may require changing the misnamed show-ref option, but also
thinking twice before changing the meaning of "--all" for the
rev-list/log family: it's easy to say "--all --linked" or "--all
--heads" to get everything plus all linked worktree heads when "--all"
== "--branches --tags HEAD", but it's more cumbersome with a changed
--all that is "really everything". I gues my suggestion would be:

--all as it is now (refs/* plus HEAD)

--head alternative way to say HEAD (as it is now for show-ref)

--heads HEAD for all linked worktrees (incompatible change for show-ref)

And all of them should work the same for the rev-list/log family as well
as for-each-ref/show-ref.

I thinking that changing show-ref (porcelain, not quite as commonly
used) should do the least harm compared to all other options.

Michael