builtin add -p: fix hunk splitting

The C reimplementation of "add -p" fails to split the last hunk in a
file if hunk ends with an addition or deletion without any post context
line unless it is the last file to be processed.

To determine whether a hunk can be split a counter is incremented each
time a context line follows an insertion or deletion. If at the end of
the hunk the value of this counter is greater than one then the hunk
can be split into that number of smaller hunks. If the last hunk in a
file ends with an insertion or deletion then there is no following
context line and the counter will not be incremented. This case is
already handled at the end of the loop where counter is incremented if
the last hunk ended with an insertion or deletion. Unfortunately there
is no similar check between files (likely because the perl version
only ever parses one diff at a time). Fix this by checking if the last
hunk ended with an insertion or deletion when we see the diff header
of a new file and extend the existing regression test.

Reproted-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

add-patch.c

@@ -383,6 +383,17 @@ static int is_octal(const char *p, size_t len)
 	return 1;
 }
 
+static void complete_file(char marker, struct hunk *hunk)
+{
+	if (marker == '-' || marker == '+')
+		/*
+		 * Last hunk ended in non-context line (i.e. it
+		 * appended lines to the file, so there are no
+		 * trailing context lines).
+		 */
+		hunk->splittable_into++;
+}
+
 static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 {
 	struct strvec args = STRVEC_INIT;
@@ -472,6 +483,7 @@ static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 			eol = pend;
 
 		if (starts_with(p, "diff ")) {
+			complete_file(marker, hunk);
 			ALLOC_GROW_BY(s->file_diff, s->file_diff_nr, 1,
 				   file_diff_alloc);
 			file_diff = s->file_diff + s->file_diff_nr - 1;
@@ -598,13 +610,7 @@ static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 				file_diff->hunk->colored_end = hunk->colored_end;
 		}
 	}
-
-	if (marker == '-' || marker == '+')
-		/*
-		 * Last hunk ended in non-context line (i.e. it appended lines
-		 * to the file, so there are no trailing context lines).
-		 */
-		hunk->splittable_into++;
+	complete_file(marker, hunk);
 
 	/* non-colored shorter than colored? */
 	if (colored_p != colored_pend) {

t/t3701-add-interactive.sh

@@ -326,7 +326,9 @@ test_expect_success 'correct message when there is nothing to do' '
 test_expect_success 'setup again' '
 	git reset --hard &&
 	test_chmod +x file &&
-	echo content >>file
+	echo content >>file &&
+	test_write_lines A B C D>file2 &&
+	git add file2
 '
 
 # Write the patch file with a new line at the top and bottom
@@ -341,13 +343,27 @@ test_expect_success 'setup patch' '
 	 content
 	+lastline
 	\ No newline at end of file
+	diff --git a/file2 b/file2
+	index 8422d40..35b930a 100644
+	--- a/file2
+	+++ b/file2
+	@@ -1,4 +1,5 @@
+	-A
+	+Z
+	 B
+	+Y
+	 C
+	-D
+	+X
 	EOF
 '
 
 # Expected output, diff is similar to the patch but w/ diff at the top
 test_expect_success 'setup expected' '
 	echo diff --git a/file b/file >expected &&
-	sed "/^index/s/ 100644/ 100755/" patch >>expected &&
+	sed -e "/^index 180b47c/s/ 100644/ 100755/" \
+	    -e /1,5/s//1,4/ \
+	    -e /Y/d patch >>expected &&
 	cat >expected-output <<-\EOF
 	--- a/file
 	+++ b/file
@@ -366,6 +382,28 @@ test_expect_success 'setup expected' '
 	 content
 	+lastline
 	\ No newline at end of file
+	--- a/file2
+	+++ b/file2
+	@@ -1,4 +1,5 @@
+	-A
+	+Z
+	 B
+	+Y
+	 C
+	-D
+	+X
+	@@ -1,2 +1,2 @@
+	-A
+	+Z
+	 B
+	@@ -2,2 +2,3 @@
+	 B
+	+Y
+	 C
+	@@ -3,2 +4,2 @@
+	 C
+	-D
+	+X
 	EOF
 '
 
@@ -373,8 +411,8 @@ test_expect_success 'setup expected' '
 test_expect_success 'add first line works' '
 	git commit -am "clear local changes" &&
 	git apply patch &&
-	test_write_lines s y y | git add -p file 2>error >raw-output &&
-	sed -n -e "s/^([1-2]\/[1-2]) Stage this hunk[^@]*\(@@ .*\)/\1/" \
+	test_write_lines s y y s y n y | git add -p 2>error >raw-output &&
+	sed -n -e "s/^([1-9]\/[1-9]) Stage this hunk[^@]*\(@@ .*\)/\1/" \
 	       -e "/^[-+@ \\\\]"/p raw-output >output &&
 	test_must_be_empty error &&
 	git diff --cached >diff &&