add -p: fix counting when splitting and coalescing

When a file has no trailing new line at the end diff records this by
appending "\ No newline at end of file" below the last line of the
file. This line should not be counted in the hunk header. Fix the
splitting and coalescing code to count files without a trailing new line
properly and change one of the tests to test splitting without a
trailing new line.

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

git-add--interactive.perl

@@ -793,6 +793,11 @@ sub split_hunk {
 		while (++$i < @$text) {
 			my $line = $text->[$i];
 			my $display = $display->[$i];
+			if ($line =~ /^\\/) {
+				push @{$this->{TEXT}}, $line;
+				push @{$this->{DISPLAY}}, $display;
+				next;
+			}
 			if ($line =~ /^ /) {
 				if ($this->{ADDDEL} &&
 				    !defined $next_hunk_start) {
@@ -891,6 +896,9 @@ sub merge_hunk {
 			$n_cnt++;
 			push @line, $line;
 			next;
+		} elsif ($line =~ /^\\/) {
+			push @line, $line;
+			next;
 		}
 
 		last if ($o1_ofs <= $ofs);
@@ -909,6 +917,9 @@ sub merge_hunk {
 			$n_cnt++;
 			push @line, $line;
 			next;
+		} elsif ($line =~ /^\\/) {
+			push @line, $line;
+			next;
 		}
 		$ofs++;
 		$o_cnt++;

t/t3701-add-interactive.sh

@@ -237,14 +237,15 @@ test_expect_success 'setup patch' '
 	 baseline
 	 content
 	+lastline
+	\ No newline at end of file
 	EOF
 '
 
-# Expected output, similar to the patch but w/ diff at the top
+# Expected output, diff is similar to the patch but w/ diff at the top
 test_expect_success 'setup expected' '
-	cat >expected <<-\EOF
-	diff --git a/file b/file
-	index b6f2c08..61b9053 100755
+	echo diff --git a/file b/file >expected &&
+	cat patch |sed "/^index/s/ 100644/ 100755/" >>expected &&
+	cat >expected-output <<-\EOF
 	--- a/file
 	+++ b/file
 	@@ -1,2 +1,4 @@
@@ -252,16 +253,30 @@ test_expect_success 'setup expected' '
 	 baseline
 	 content
 	+lastline
+	\ No newline at end of file
+	@@ -1,2 +1,3 @@
+	+firstline
+	 baseline
+	 content
+	@@ -1,2 +2,3 @@
+	 baseline
+	 content
+	+lastline
+	\ No newline at end of file
 	EOF
 '
 
 # Test splitting the first patch, then adding both
-test_expect_success 'add first line works' '
+test_expect_success C_LOCALE_OUTPUT 'add first line works' '
 	git commit -am "clear local changes" &&
 	git apply patch &&
-	(echo s; echo y; echo y) | git add -p file &&
-	git diff --cached > diff &&
-	diff_cmp expected diff
+	printf "%s\n" s y y | git add -p file 2>error |
+		sed -n -e "s/^Stage this hunk[^@]*\(@@ .*\)/\1/" \
+		       -e "/^[-+@ \\\\]"/p  >output &&
+	test_must_be_empty error &&
+	git diff --cached >diff &&
+	diff_cmp expected diff &&
+	test_cmp expected-output output
 '
 
 test_expect_success 'setup expected' '