[PATCH v3 2/5] add -p: gracefully ignore unparseable hunk headers in colored diffs

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

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.

Let's punt for now and simply show nothing apart from the line range in
that case.

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

Reported-by: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 add-patch.c                | 15 ++++++---------
 t/t3701-add-interactive.sh |  9 +++++++++
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/add-patch.c b/add-patch.c
index 509ca04456b..f2fffe1af02 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -357,16 +357,13 @@ static int parse_hunk_header(struct add_p_state *s, struct hunk *hunk)
 	eol = memchr(line, '\n', s->colored.len - hunk->colored_start);
 	if (!eol)
 		eol = s->colored.buf + s->colored.len;
-	p = memmem(line, eol - line, "@@ -", 4);
-	if (!p)
-		return error(_("could not parse colored hunk header '%.*s'"),
-			     (int)(eol - line), line);
-	p = memmem(p + 4, eol - p - 4, " @@", 3);
-	if (!p)
-		return error(_("could not parse colored hunk header '%.*s'"),
-			     (int)(eol - line), line);
 	hunk->colored_start = eol - s->colored.buf + (*eol == '\n');
-	header->colored_extra_start = p + 3 - s->colored.buf;
+	p = memmem(line, eol - line, "@@ -", 4);
+	if (p && (p = memmem(p + 4, eol - p - 4, " @@", 3)))
+		header->colored_extra_start = p + 3 - s->colored.buf;
+	else
+		/* could not parse colored hunk header, showing nothing */
+		header->colored_extra_start = hunk->colored_start;
 	header->colored_extra_end = hunk->colored_start;
 
 	return 0;
diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
index 88d8133f38f..c2187f9cec8 100755
--- a/t/t3701-add-interactive.sh
+++ b/t/t3701-add-interactive.sh
@@ -766,6 +766,15 @@ test_expect_success 'detect bogus diffFilter output' '
 	force_color test_must_fail git add -p <y
 '
 
+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/g" \
+		add -p <n
+'
+
 test_expect_success 'handle very large filtered diff' '
 	git reset --hard &&
 	# The specific number here is not important, but it must
-- 
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