Re: [PATCH] glossary: describe "worktree"

[Han-Wen Nienhuys <hanwen@google.com>]

On Thu, Feb 10, 2022 at 8:14 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Han-Wen Nienhuys <hanwen@google.com> writes:
>
> > on a tangent: I posted a patch to write MERGE_AUTOSTASH,
> > rebase-merge/autostash, etc. as refs.
> > Is that the right direction? They are read like refs, but they are
> > together in a directory with other bits of stateful data (similar to
> > what is appended to FETCH_HEAD). Perhaps I should rather change the
> > read path, so they're always read as files rather than refs?
>
> I think that would be a lot more preferrable.  If a file is written
> to record pieces of info, among which an object name happens to be
> included, it does not have to be recorded as a ref.  Especially if
> it is an ephemeral file like MERGE_AUTOSTASH and FETCH_HEAD.

For FETCH_HEAD, doing

  git fetch host refs/changes/23/123/1 && git checkout FETCH_HEAD

is the standard idiom for downloading a change from Gerrit. I suspect
there might be other similar idioms. This means we have to read them
through the refs machinery.

I think the most sensible approach is to pass the read/write through
refs_* functions, but special-case the storage, so it doesn't go
through reftable. We already do this for FETCH_HEAD and MERGE_HEAD in
refs_read_raw_refs.

This means we need a formal definition of which refs should be treated
as files. Maybe we could do as follows:

Pseudorefs are
  1) all uppercase toplevel names except for HEAD
  2) all refs that are not under refs/* (for example:
rebase-{merge,apply}/autostash)

Pseudorefs are always stored as files containing a hex object_id.

Pseudorefs can be read or written through refs_* functions, but given
the storage guarantees, it's also valid to read/write them outside
refs_* functions

It is forbidden to make cross-ref transactions that involve pseudorefs.

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Han-Wen Nienhuys - Google Munich
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