On Wed, May 20, 2020 at 6:06 PM Han-Wen Nienhuys [off-list ref] wrote:

quoted

quoted

+The `message_length` may be 0, in which case there was no message
+supplied for the update.
+
+Contrary to traditional reflog (which is a file), renames are encoded as
+a combination of ref deletion and ref creation.

Yay?  How does the deletion record look like?  The new object name
being 0*hashlength?  I didn't see it defined in the description (and
I am guessing that log_type of 0x0 is *NOT* used for that purpose).

quoting the spec:

"Log record entries use `log_type` to indicate what follows:

* `0x0`: deletion; no log data."

quoted

So, NEEDSWORK: describe how "creation of a ref" and "deletion of a ref"
appears in a log as a log record entry.

the creation would be the appearance of a reflog record for the ref.
You'd have to search back in time to decide if a reflog record it was
an update to an existing record or a creation.

Correction. This is one of the things that confused me earlier: reflog
entries for creating and deleting branches look like this

    000000000000 -> xxxxx      (create)
    xxxxxx.. xx        -> 00000 .. (delete)

respectively. When the rename happens, we can signal that the deletion
and addition are linked, because they occur at the same update_index.

The deletion records for logs (type=0x0) remove a reflog entry at a
specific (earlier used) update_index. So you could have the following
situation:

0x0001.ref : reflog "refs/heads/master" @ update_index=0x0001,
new=xxx, old=yyy ...

and then a subsequent table could specify

0x0020.ref : reflog "refs/heads/master" @ update_index=0x0001 (type=0x0)

which would hide the earlier reflog entry.

Jonathan Nieder said that this is used for git-stash, but I have never
understood why this is necessary, and would love to clarify this
better.

I'll clarify the explanation to reflect this.

-- 
Han-Wen Nienhuys - Google Munich
I work 80%. Don't expect answers from me on Fridays.
--
Google Germany GmbH, Erika-Mann-Strasse 33, 80636 Munich
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado