Subject: [PATCH 2/2] add-patch: update hunk splitability after editing

From: "Phillip Wood via GitGitGadget" <[email-masked]>
Date: Fri, 21 Feb 2025 14:57:17 +0000

From: Phillip Wood <[email-masked]>

When the users edits a hunk if they change deletion lines to context
lines or vice versa then the number of hunks that the edited hunk can be
split into may differ from the unedited hunk and so we need to update
hunk->splittable_into. In practice users are unlikely to hit this bug as
it is doubtful that a user who has edited a hunk will split it
afterwards.

Signed-off-by: Phillip Wood <[email-masked]>
---
 add-patch.c                | 12 +++++++++++-
 t/t3701-add-interactive.sh | 21 +++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/add-patch.c b/add-patch.c
index f44f98275cc..982745373df 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -1182,19 +1182,29 @@ static ssize_t recount_edited_hunk(struct add_p_state *s, struct hunk *hunk,
 {
 	struct hunk_header *header = &hunk->header;
 	size_t i;
+	char ch, marker = ' ';
 
+	hunk->splittable_into = 0;
 	header->old_count = header->new_count = 0;
 	for (i = hunk->start; i < hunk->end; ) {
-		switch(normalize_marker(&s->plain.buf[i])) {
+		ch = normalize_marker(&s->plain.buf[i]);
+		switch (ch) {
 		case '-':
 			header->old_count++;
+			if (marker == ' ')
+				hunk->splittable_into++;
+			marker = ch;
 			break;
 		case '+':
 			header->new_count++;
+			if (marker == ' ')
+				hunk->splittable_into++;
+			marker = ch;
 			break;
 		case ' ':
 			header->old_count++;
 			header->new_count++;
+			marker = ch;
 			break;
 		}
 
diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
index 760f3d0d30f..cb81bfe64c8 100755
--- a/t/t3701-add-interactive.sh
+++ b/t/t3701-add-interactive.sh
@@ -1240,4 +1240,25 @@ test_expect_success 'splitting previous hunk marks split hunks as undecided' '
 	test_cmp expect actual
 '
 
+test_expect_success 'splitting edited hunk' '
+	# Before the first hunk is edited it can be split into two
+	# hunks, after editing it can be split into three hunks.
+
+	write_script fake-editor.sh <<-\EOF &&
+	sed "s/^ c/-c/" "$1" >"$1.tmp" &&
+	mv "$1.tmp" "$1"
+	EOF
+
+	test_write_lines a b c d e f g h i j k l m n>file &&
+	git add file &&
+	test_write_lines A b c d E f g h i j k l M n >file &&
+	(
+		test_set_editor "$(pwd)/fake-editor.sh" &&
+		test_write_lines e K s j y n y q | git add -p file
+	) &&
+	git cat-file blob :file >actual &&
+	test_write_lines a b d e f g h i j k l M n >expect &&
+	test_cmp expect actual
+'
+
 test_done
-- 
gitgitgadget