Re: CFT: merge-recursive in C (updated)

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Jun 29, 2006, 18:40 UTC
Message-ID: <Pine.LNX.4.63.0606291945200.29667@wbgn013.biozentrum.uni-wuerzburg.de>
In-Reply-To: <81b0412b0606290143g5a3a0f5atbda3f4250411e92e@mail.gmail.com>

Hi,

On Thu, 29 Jun 2006, Alex Riesen wrote:

Show 35 quoted lines

> [cc list restored, I'm lost in the maze of git update-index, all cache
> changing functions looking almost the same]
> 
> On 6/29/06, Junio C Hamano <junkio@cox.net> wrote:
> > > this broke t6022-merge-rename.sh (the second test). It produces an
> > > index with this:
> > >
> > > .../t/trash$ git-diff-index white
> > > :100644 100644 2d603156dc5bdf6295c789cac08e3c9942a0b82a
> > 0000000000000000000000000000000000000000 M      B
> > > :100644 100644 ba41fb96393979b22691106b06bf5231eab57b85
> > 0000000000000000000000000000000000000000 M      N
> > >
> > > whereas git-merge-recursive (and the previous version, without pipe):
> > >
> > > .../t/trash$ git-diff-index white
> > > :100644 100644 2d603156dc5bdf6295c789cac08e3c9942a0b82a
> > 0000000000000000000000000000000000000000 M      B
> > >
> > > I can see that "git update-index --add" is somehow different from a
> > > pipe to "git update-index --index-info", but not very clear. Does this
> > > "zero-sha1" mean that the file "N" is not in the index?
> > 
> > When diff-index and diff-files compare a tree entry or an index
> > entry with a file in the working tree, they do not compute the
> > blob hash value for the file in the working tree.  0{40} is used
> > on the RHS in such a case.  When the working tree file matches
> > the corresponding index entry, then we know RHS matches what is
> > in the index, so both sides have the blob hash value.
> 
> Ok. Am I correct in the assumption, that if the file in working tree has
> the same SHA1 as LHS, than the next "git-update-index --refresh" will
> remove the entry from git-diff-index output?
> This is what actually happens, if I do "git-update-index --refresh", so I
> suspect that I have an SHA1 update gone missing somewhere.

I think the problem is more like this (in ce_match_stat_basic()):

        if (ce->ce_mtime.sec != htonl(st->st_mtime))
                changed |= MTIME_CHANGED;
        if (ce->ce_ctime.sec != htonl(st->st_ctime))
                changed |= CTIME_CHANGED;

If you update with --index-info, the mtime and ctime is not updated from the file in the working directory.

All the more a reason to go forward with direct calls to read_cache() and write_cache(). At the moment, my plan is

- trivially split the read_cache() code into read_cache()/read_cache_from(),
- introduce flush_cache(),
- trivially rewrite add_file_to_cache(), and add_cache_info() from
  builtin-update-index.c, move that to read-tree.c, too, and
- throw out the pipe to git-update-index from merge-recursive.c 
  altogether.

This should be less intrusive than it sounds: with the introduction of read_cache_from() it should be trivial to handle the problem of different index files.

We have to put a lock_file on the index file at the start, and write the index file at the end.

Ciao, Dscho