[PATCH] add--interactive: allow custom diff highlighting programs

From: Jeff King <peff@peff.net>
Date: Feb 27, 2016, 05:37 UTC
Message-ID: <20160227053706.GA21117@sigill.intra.peff.net>

The patch hunk selector of add--interactive knows how ask git for colorized diffs, and correlate them with the uncolored diffs we apply. But there's not any way for somebody who uses a diff-filter tool like contrib's diff-highlight to see their normal highlighting.

This patch lets users define an arbitrary shell command to pipe the colorized diff through. The exact output shouldn't matter (since we just show the result to humans) as long as it is line-compatible with the original diff (so that hunk-splitting can split the colorized version, too).

I left two minor issues with the new system that I don't think are worth fixing right now, but could be done later:

  1. We only filter colorized diffs. Theoretically a user
     could want to filter a non-colorized diff, but I find
     it unlikely in practice. Users who are doing things
     like diff-highlighting are likely to want color, too.

  2. add--interactive will re-colorize a diff which has been
     hand-edited, but it won't have run through the filter.
     Fixing this is conceptually easy (just pipe the diff
     through the filter), but practically hard to do without
     using tempfiles (it would need to feed data to and read
     the result from the filter without deadlocking; this
     raises portability questions with respect to Windows).

I've punted on both issues for now, and if somebody really cares later, they can do a patch on top.

Signed-off-by: Jeff King <peff@peff.net>
---
This is a little hack I whipped up after the diff-so-fancy people asked
me about it in:

  https://github.com/so-fancy/diff-so-fancy/issues/35

It's something I've wanted for a while with diff-highlight. I made sure it works (the final hunk of this patch was added via highlighted "add -p". Woohoo!), but other than that it hasn't been exposed to a lot of corner cases.

I'm actually not sure whether it will work well with diff-so-fancy or not; they change the diff header around a bit, and there's not a complete 1:1 correspondence in the lines. _But_ I think it might work OK in practice, because their diff header remains 4 lines long, and the hunks themselves have 1:1 line correspondence.

 Documentation/config.txt  |  8 ++++++++
 git-add--interactive.perl | 12 ++++++++++--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 2cd6bdd..f5834ec 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1886,6 +1886,14 @@ interactive.singleKey::
 	setting is silently ignored if portable keystroke input
 	is not available; requires the Perl module Term::ReadKey.
 
+interactive.diffFilter::
+	When an interactive command (such as `git add --patch`) shows
+	a colorized diff, git will pipe the diff through the shell
+	command defined by this configuration variable. The command may
+	mark up the diff further for human consumption, provided that it
+	retains a one-to-one correspondence with the lines in the
+	original diff. Defaults to disabled (no filtering).
+
 log.abbrevCommit::
 	If true, makes linkgit:git-log[1], linkgit:git-show[1], and
 	linkgit:git-whatchanged[1] assume `--abbrev-commit`. You may
diff --git a/git-add--interactive.perl b/git-add--interactive.perl
index 77876d4..822f857 100755
--- a/git-add--interactive.perl
+++ b/git-add--interactive.perl
@@ -45,6 +45,7 @@ my ($diff_new_color) =
 my $normal_color = $repo->get_color("", "reset");
 
 my $diff_algorithm = $repo->config('diff.algorithm');
+my $diff_filter = $repo->config('interactive.difffilter');
 
 my $use_readkey = 0;
 my $use_termcap = 0;
@@ -754,7 +755,14 @@ sub parse_diff {
 	my @diff = run_cmd_pipe("git", @diff_cmd, "--", $path);
 	my @colored = ();
 	if ($diff_use_color) {
-		@colored = run_cmd_pipe("git", @diff_cmd, qw(--color --), $path);
+		my @display_cmd = ("git", @diff_cmd, qw(--color --), $path);
+		if (defined $diff_filter) {
+			# quotemeta is overkill, but sufficient for shell-quoting
+			my $diff = join(' ', map { quotemeta } @display_cmd);
+			@display_cmd = ("$diff | $diff_filter");
+		}
+
+		@colored = run_cmd_pipe(@display_cmd);
 	}
 	my (@hunk) = { TEXT => [], DISPLAY => [], TYPE => 'header' };
 
@@ -765,7 +773,7 @@ sub parse_diff {
 		}
 		push @{$hunk[-1]{TEXT}}, $diff[$i];
 		push @{$hunk[-1]{DISPLAY}},
-			($diff_use_color ? $colored[$i] : $diff[$i]);
+			(@colored ? $colored[$i] : $diff[$i]);
 	}
 	return @hunk;
 }

-- 
2.7.2.767.g705917e