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

[Stefan Beller <sbeller@google.com>]

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.

Stefan