add -p: gracefully handle unparseable hunk headers in colored diffs

In
https://lore.kernel.org/git/ecf6f5be-22ca-299f-a8f1-bda38e5ca246@gmail.com,
Phillipe Blain reported that the built-in `git add -p` command fails
when asked to use [`diff-so-fancy`][diff-so-fancy] to colorize the diff.

The reason is that this tool produces colored diffs with a hunk header
that does not contain any parseable `@@ ... @@` line range information,
and therefore we cannot detect any part in that header that comes after
the line range.

As proposed by Phillip Wood, let's take that for a clear indicator that
we should show the hunk headers verbatim. This is what the Perl version
of the interactive `add` command did, too.

[diff-so-fancy]: https://github.com/so-fancy/diff-so-fancy

Reported-by: Philippe Blain <levraiphilippeblain@gmail.com>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
index 6b1137e7c9..447fc3380a 100755
--- a/t/t3701-add-interactive.sh
+++ b/t/t3701-add-interactive.sh
@@ -767,6 +767,16 @@ test_expect_success 'detect bogus diffFilter output' '
 	grep "mismatched output" output
 '
 
+test_expect_success 'handle iffy colored hunk headers' '
+	git reset --hard &&
+
+	echo content >test &&
+	printf n >n &&
+	force_color git -c interactive.diffFilter="sed s/.*@@.*/XX/" \
+		add -p >output 2>&1 <n &&
+	grep "^XX$" output
+'
+
 test_expect_success 'diff.algorithm is passed to `git diff-files`' '
 	git reset --hard &&