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

> On Tue, Dec 5, 2017 at 5:13 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.
> 
> This commit message does a good job of explaining the issue, so
> someone who hasn't followed the thread (or has not followed it
> closely, like me) can understand the problem and solution. Thanks.
> 
> A few comments below...
> 
> > Reported-by: Ben Boeckel <ben.boeckel@kitware.com>
> > Signed-off-by: Brandon Williams <bmwill@google.com>
> > ---
> > diff --git 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();
> 
> 557a5998d (submodule: remove gitmodules_config, 2017-08-03) touched a
> fair number of built-in commands. It's not clear from the current
> patch's commit message if diff-tree is the only command which
> regressed. Is it? Or are other commands also likely to have regressed?
> Perhaps the commit message could say something about this. For
> instance: "All other commands touched by 557a5998d have been audited
> and were found to be regression-free" or "Other commands may regress
> in the same way, but we will take a wait-and-see attitude and fix them
> as needed because <fill-in-reason>".

> 
> > diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
> > @@ -636,6 +636,23 @@ test_expect_success 'check with space before tab in indent (diff-tree)' '
> > +test_expect_success 'check with ignored trailing whitespace attr (diff-tree)' '
> > +       test_when_finished "git reset --hard HEAD^" &&
> 
> A few style nits...
> 
> > +       # Create a whitespace error that should be ignored.
> 
> Comments in nearby tests are not capitalized and do not end with period.
> 
> > +       echo "* -whitespace" > ".gitattributes" &&
> 
> Please drop unnecessary quotes around the filename, as the extra noise
> makes it a bit harder to read. Also, lose space after redirection
> operator:
> 
>     echo "* -whitespace" >.gitattributes &&
> 
> > +       git add ".gitattributes" &&
> > +       echo "trailing space -> " > "trailing-space" &&
> 
> All the nearby tests use some variation of:
> 
>     echo "foo ();  " >x &&
> 
> which differs from the "trailing space ->" and filename
> 'trailing-space' used in this test. Lack of consistency makes this new
> test stick out like a sore thumb.

> 
> > +       git add "trailing-space" &&
> > +       git commit -m "trailing space" &&
> > +
> > +       # With a worktree diff-tree ignores the whitespace error
> > +       git diff-tree --root --check HEAD &&
> > +
> > +       # Without a worktree diff-tree still ignores the whitespace error
> > +       git -C .git diff-tree --root --check HEAD
> > +'