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

[Eric Sunshine <sunshine@sunshineco.com>]

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
> +'