Re: [PATCH 1/1] read-cache: update index format default to v4

[Matthias Sohn <matthias.sohn@gmail.com>]

On Tue, Sep 25, 2018 at 8:01 PM Stefan Beller <sbeller@google.com> wrote:
>
> On Tue, Sep 25, 2018 at 7:30 AM Derrick Stolee <stolee@gmail.com> wrote:
> >
> > On 9/25/2018 3:06 AM, Patrick Steinhardt wrote:
> > > On Mon, Sep 24, 2018 at 11:32:23PM +0200, SZEDER Gábor wrote:
> > >> On Mon, Sep 24, 2018 at 02:15:30PM -0700, Derrick Stolee via GitGitGadget wrote:
> > >>> From: Derrick Stolee <dstolee@microsoft.com>
> > >>>
> > >>> The index v4 format has been available since 2012 with 9d22778
> > >>> "reach-cache.c: write prefix-compressed names in the index". Since
> > >>> the format has been stable for so long, almost all versions of Git
> > >>> in use today understand version 4, removing one barrier to upgrade
> > >>> -- that someone may want to downgrade and needs a working repo.
> > >> What about alternative implementations, like JGit, libgit2, etc.?
> > > Speaking of libgit2, we are able to read and write index v4 since
> > > commit c1b370e93
> >
> > This is a good point, Szeder.
> >
> > Patrick: I'm glad LibGit2 is up-to-date with index formats.
> >
> > Unfortunately, taking a look (for the first time) at the JGit code
> > reveals that they don't appear to have v4 support. In
> > org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCache.java, the
> > DirCache.readFrom() method: lines 488-494, I see the following snippet:
> >
> >                  final int ver = NB.decodeInt32(hdr, 4);
> >                  boolean extended = false;
> >                  if (ver == 3)
> >                          extended = true;
> >                  else if (ver != 2)
> >                          throw new
> > CorruptObjectException(MessageFormat.format(
> > JGitText.get().unknownDIRCVersion, Integer.valueOf(ver)));
> >
> > It looks like this will immediately throw with versions other than 2 or 3.
> >
> > I'm adding Jonathan Nieder to CC so he can check with JGit people about
> > the impact of this change.
>
> JGit is used both on the server (which doesn't use index/staging area)
> as well as client side as e.g. an Eclipse integration, which would
> very much like to use the index.
>
> Adding Matthias Sohn as well, who is active in JGit and cares
> more about the client side than Googlers who only make use
> of the server side part of JGit.

thanks for the heads up, in fact JGit does not yet support index version 4.
I will look into this.

-Matthias