Re: [Bug report] diff.noprefix config is ignored for interactive `add`

[Jeff King <peff@peff.net>]

On Tue, Apr 06, 2021 at 12:15:28PM +0200, Nikita Bobko wrote:

> Steps to reproduce:
> 1. Run `git -c diff.noprefix=true add -p`
> 
> Expected behavior:
> `a/` and `b/` prefixes are not shown during interactive `add`
> like this:
> [...]
> Actual behavior:
> `a/` and `b/` prefixes are shown instead. Like this:

That's not too surprising. The add-interactive script is built around
the diff-tree plumbing command, which does not respect a lot of
"cosmetic" config, especially if it would make the diff hard to parse.
So the add-interactive command would have to manually plumb through the
config option, like we do for some other options.

In this case, I think you'd want to enable the option only for the
version of the diff we show to the user (since the machine-readable one
has to actually be parsed by git-apply). This is what we do for
supporting color diffs, for example.

I imagine something like this:

diff --git a/git-add--interactive.perl b/git-add--interactive.perl
index bc3a1e8eff..1a249e15cb 100755
--- a/git-add--interactive.perl
+++ b/git-add--interactive.perl
@@ -43,6 +43,12 @@
 		$repo->get_color('color.diff.new', 'green'),
 	) : ();
 
+# options to feed to diff to produce human-readable version
+my @human_diff_opts = (
+	$diff_use_color ? '--color' : (),
+	$repo->config_bool('diff.noprefix') ? qw(--no-prefix) : (),
+);
+
 my $normal_color = $repo->get_color("", "reset");
 
 my $diff_algorithm = $repo->config('diff.algorithm');
@@ -714,8 +720,8 @@ sub parse_diff {
 	}
 	my @diff = run_cmd_pipe("git", @diff_cmd, qw(--no-color --), $path);
 	my @colored = ();
-	if ($diff_use_color) {
-		my @display_cmd = ("git", @diff_cmd, qw(--color --), $path);
+	if (@human_diff_opts) {
+		my @display_cmd = ("git", @diff_cmd, @human_diff_opts, '--', $path);
 		if (defined $diff_filter) {
 			# quotemeta is overkill, but sufficient for shell-quoting
 			my $diff = join(' ', map { quotemeta } @display_cmd);

would work, but I didn't really test it. There's another hitch, which is
that this subsystem has all been re-written in C. So we'd really want to
implement it in the new code (possibly in both places, though maybe it
is time to consider cutting over from the perl script to the C one by
deafult?).

But hopefully this illustrates the general idea, and gives somebody
interested in the feature enough to work up their own patch.

-Peff