Re: [PATCH] diff-tree: read the index so attribute checks work in bare repositories

> On Tue, Dec 5, 2017 at 2:13 PM, Brandon Williams <bmwill@google.com> wrote:
> > A regression was introduced in 557a5998d (submodule: remove
> > gitmodules_config, 2017-08-03) to how attribute processing was handled
> > in bare repositories when running the diff-tree command.
> >
> > By default the attribute system will first try to read ".gitattribute"
> > files from the working tree and then falls back to reading them from the
> > index if there isn't a copy checked out in the worktree.  Prior to
> > 557a5998d the index was read as a side effect of the call to
> > 'gitmodules_config()' which ensured that the index was already populated
> > before entering the attribute subsystem.
> >
> > Since the call to 'gitmodules_config()' was removed the index is no
> > longer being read so when the attribute system tries to read from the
> > in-memory index it doesn't find any ".gitattribute" entries effectively
> > ignoring any configured attributes.
> >
> > Fix this by explicitly reading the index during the setup of diff-tree.
> >
> > Reported-by: Ben Boeckel <ben.boeckel@kitware.com>
> > Signed-off-by: Brandon Williams <bmwill@google.com>
> > ---
> >
> > This patch should fix the regression.  Let me know if it doesn't solve the
> > issue and I'll investigate some more.
> >
> 
> Thanks for fixing this bug! The commit message is helpful
> to understand how this bug could slip in!
> 
> > diff --git a/builtin/diff-tree.c b/builtin/diff-tree.c
> > index d66499909..cfe7d0281 100644
> > --- a/builtin/diff-tree.c
> > +++ b/builtin/diff-tree.c
> > @@ -110,6 +110,7 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
> >
> >         git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
> >         init_revisions(opt, prefix);
> > +       read_cache();
> 
> 
> Although we do have very few unchecked calls to read_cache, I'd suggest
> to avoid spreading them. Most of the read_cache calls are guarded via:
> 
>     if (read_cache() < 0)
>         die(_("index file corrupt"));

> 
> I wonder if this hints at a bad API, and we'd rather have read_cache
> die() on errors, and the few callers that try to get out of trouble might
> need to use read_cache_gently() instead.
> (While this potentially large refactoring may be deferred, I'd ask for
> an if at least)
> 
> Thanks,
> Stefan