diff --no-index: reset temporary buffer lengths on directory iteration

Commit 875b91b (diff --no-index: use strbuf for temporary pathnames,
2012-04-25) introduced a regression when using diff --no-index with
directories.  When iterating through a directory, the switch to strbuf
from heap-allocated char arrays caused paths to form like 'dir/file1',
'dir/file1file2', rather than 'dir/file1', 'dir/file2' as expected.

Avoid this by resetting the paths variables to their original length
before each iteration.

Signed-off-by: Bobby Powers <bobbypowers@gmail.com>
Reviewed-by: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-no-index.c

@@ -68,6 +68,7 @@ static int queue_diff(struct diff_options *o,
 		struct string_list p1 = STRING_LIST_INIT_DUP;
 		struct string_list p2 = STRING_LIST_INIT_DUP;
 		int i1, i2, ret = 0;
+		size_t len1 = 0, len2 = 0;
 
 		if (name1 && read_directory(name1, &p1))
 			return -1;
@@ -80,18 +81,23 @@ static int queue_diff(struct diff_options *o,
 			strbuf_addstr(&buffer1, name1);
 			if (buffer1.len && buffer1.buf[buffer1.len - 1] != '/')
 				strbuf_addch(&buffer1, '/');
+			len1 = buffer1.len;
 		}
 
 		if (name2) {
 			strbuf_addstr(&buffer2, name2);
 			if (buffer2.len && buffer2.buf[buffer2.len - 1] != '/')
 				strbuf_addch(&buffer2, '/');
+			len2 = buffer2.len;
 		}
 
 		for (i1 = i2 = 0; !ret && (i1 < p1.nr || i2 < p2.nr); ) {
 			const char *n1, *n2;
 			int comp;
 
+			strbuf_setlen(&buffer1, len1);
+			strbuf_setlen(&buffer2, len2);
+
 			if (i1 == p1.nr)
 				comp = 1;
 			else if (i2 == p2.nr)

t/t4053-diff-no-index.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+test_description='diff --no-index'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	mkdir a &&
+	mkdir b &&
+	echo 1 >a/1 &&
+	echo 2 >a/2
+'
+
+test_expect_success 'git diff --no-index directories' '
+	git diff --no-index a b >cnt
+	test $? = 1 && test_line_count = 14 cnt
+'
+
+test_done