add -p: fix checkout -p with pathological context

Commit fecc6f3a68 ("add -p: adjust offsets of subsequent hunks when one is
skipped", 2018-03-01) fixed adding hunks in the correct place when a
previous hunk has been skipped. However it did not address patches that
are applied in reverse. In that case we need to adjust the pre-image
offset so that when apply reverses the patch the post-image offset is
adjusted correctly. We subtract rather than add the delta as the patch
is reversed (the easiest way to think about it is to consider a hunk of
deletions that is skipped - in that case we want to reduce offset so we
need to subtract).

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/git-add--interactive.perl b/git-add--interactive.perl
index 8361ef45e7..85d0dc1196 100755
--- a/git-add--interactive.perl
+++ b/git-add--interactive.perl
@@ -957,7 +957,11 @@ sub coalesce_overlapping_hunks {
 			next;
 		}
 		if ($ofs_delta) {
-			$n_ofs += $ofs_delta;
+			if ($patch_mode_flavour{IS_REVERSE}) {
+				$o_ofs -= $ofs_delta;
+			} else {
+				$n_ofs += $ofs_delta;
+			}
 			$_->{TEXT}->[0] = format_hunk_header($o_ofs, $o_cnt,
 							     $n_ofs, $n_cnt);
 		}