[PATCH v5 6/9] add -p: adjust offsets of subsequent hunks when one is skipped

[Phillip Wood <phillip.wood@talktalk.net>]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

Since commit 8cbd431082 ("git-add--interactive: replace hunk
recounting with apply --recount", 2008-7-2) if a hunk is skipped then
we rely on the context lines to apply subsequent hunks in the right
place. While this works most of the time it is possible for hunks to
end up being applied in the wrong place. To fix this adjust the offset
of subsequent hunks to correct for any change in the number of
insertions or deletions due to the skipped hunk. The change in offset
due to edited hunks that have the number of insertions or deletions
changed is ignored here, it will be fixed in the next commit.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 git-add--interactive.perl  | 15 +++++++++++++--
 t/t3701-add-interactive.sh |  2 +-
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/git-add--interactive.perl b/git-add--interactive.perl
index 8ababa6453..7a0a5896bb 100755
--- a/git-add--interactive.perl
+++ b/git-add--interactive.perl
@@ -926,14 +926,25 @@ sub coalesce_overlapping_hunks {
 	my @out = ();
 
 	my ($last_o_ctx, $last_was_dirty);
+	my $ofs_delta = 0;
 
-	for (grep { $_->{USE} } @in) {
+	for (@in) {
 		if ($_->{TYPE} ne 'hunk') {
 			push @out, $_;
 			next;
 		}
 		my $text = $_->{TEXT};
-		my ($o_ofs) = parse_hunk_header($text->[0]);
+		my ($o_ofs, $o_cnt, $n_ofs, $n_cnt) =
+						parse_hunk_header($text->[0]);
+		unless ($_->{USE}) {
+			$ofs_delta += $o_cnt - $n_cnt;
+			next;
+		}
+		if ($ofs_delta) {
+			$n_ofs += $ofs_delta;
+			$_->{TEXT}->[0] = format_hunk_header($o_ofs, $o_cnt,
+							     $n_ofs, $n_cnt);
+		}
 		if (defined $last_o_ctx &&
 		    $o_ofs <= $last_o_ctx &&
 		    !$_->{DIRTY} &&
diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
index 094eeca405..e3150a4e07 100755
--- a/t/t3701-add-interactive.sh
+++ b/t/t3701-add-interactive.sh
@@ -544,7 +544,7 @@ test_expect_success 'set up pathological context' '
 	test_write_lines +b " a" >patch
 '
 
-test_expect_failure 'add -p works with pathological context lines' '
+test_expect_success 'add -p works with pathological context lines' '
 	git reset &&
 	printf "%s\n" n y |
 	git add -p &&
-- 
2.16.2