[PATCH alt-v2] Improve function dir.c:trim_trailing_spaces()

[Pasha Bolokhov <pasha.bolokhov@gmail.com>]

Discard the unnecessary 'nr_spaces' variable, remove 'strlen()' and
improve the 'if' structure. Switch to pointers instead of integers

Slightly more rare occurrences of 'text  \    ' with a backslash
in between spaces are handled correctly. Namely, the code in
8ba87adad6 does not reset 'last_space' when a backslash is
encountered and the above line stays intact as a result.
Add a test at the end of t/t0008-ignores.sh to exhibit this behavior

Signed-off-by: Pasha Bolokhov <pasha.bolokhov@gmail.com>
---
After correcting for the trailing backslash 'text\', a switch()
structure gives better readability than nested 'ifs', the way I see it.
Add a test to show that the trailing backslash 'text\' is handled
correctly

 dir.c              | 35 ++++++++++++++++++++---------------
 t/t0008-ignores.sh | 23 +++++++++++++++++++++++
 2 files changed, 43 insertions(+), 15 deletions(-)

diff --git a/dir.c b/dir.c
index eb6f581..06483d4 100644
--- a/dir.c
+++ b/dir.c
@@ -508,21 +508,26 @@ void clear_exclude_list(struct exclude_list *el)
 
 static void trim_trailing_spaces(char *buf)
 {
-	int i, last_space = -1, nr_spaces, len = strlen(buf);
-	for (i = 0; i < len; i++)
-		if (buf[i] == '\\')
-			i++;
-		else if (buf[i] == ' ') {
-			if (last_space == -1) {
-				last_space = i;
-				nr_spaces = 1;
-			} else
-				nr_spaces++;
-		} else
-			last_space = -1;
-
-	if (last_space != -1 && last_space + nr_spaces == len)
-		buf[last_space] = '\0';
+	char *p, *last_space = NULL;
+
+	for (p = buf; *p; p++)
+		switch (*p) {
+		case ' ':
+			if (!last_space)
+				last_space = p;
+			break;
+
+		case '\\':
+			p++;
+			if (!*p)
+				return;
+
+		default:
+			last_space = NULL;
+		}
+
+	if (last_space)
+		*last_space = '\0';
 }
 
 int add_excludes_from_file_to_list(const char *fname,
diff --git a/t/t0008-ignores.sh b/t/t0008-ignores.sh
index 63beb99..4cea858 100755
--- a/t/t0008-ignores.sh
+++ b/t/t0008-ignores.sh
@@ -806,4 +806,27 @@ test_expect_success !MINGW 'quoting allows trailing whitespace' '
 	test_cmp err.expect err
 '
 
+test_expect_success NOT_MINGW,NOT_CYGWIN 'correct handling of backslashes' '
+	rm -rf whitespace &&
+	mkdir whitespace &&
+	>"whitespace/trailing 1  "	&&
+	>"whitespace/trailing 2 \\\\"	&&
+	>"whitespace/trailing 3 \\\\"	&&
+	>"whitespace/trailing 4   \\ "	&&
+	>"whitespace/trailing 5 \\ \\ "	&&
+	>"whitespace/trailing 6 \\a\\"	&&
+	>whitespace/untracked &&
+	echo "whitespace/trailing 1 \\    "			>ignore  &&
+	echo "whitespace/trailing 2 \\\\\\\\\\\\\\\\"		>>ignore &&
+	echo "whitespace/trailing 3 \\\\\\\\\\\\\\\\ "		>>ignore &&
+	echo "whitespace/trailing 4   \\\\\\\\\\\\    "		>>ignore &&
+	echo "whitespace/trailing 5 \\\\\\\\ \\\\\\\\\\\\   "	>>ignore &&
+	echo "whitespace/trailing 6 \\\\\\\\a\\\\\\\\"		>>ignore &&
+	echo whitespace/untracked >expect &&
+	: >err.expect &&
+	git ls-files -o -X ignore whitespace >actual 2>err &&
+	test_cmp expect actual &&
+	test_cmp err.expect err
+'
+
 test_done
-- 
1.9.1