dir.c:trim_trailing_spaces(): fix for " \ " sequence

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

Slightly more rare occurrences of 'text  \    ' with a backslash
in between spaces are handled correctly.  Namely, the code in
7e2e4b3 (dir: ignore trailing spaces in exclude patterns, 2014-02-09)
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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

dir.c

@@ -508,21 +508,25 @@ 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;
+			/* fallthrough */
+		default:
+			last_space = NULL;
+		}
+
+	if (last_space)
+		*last_space = '\0';
 }
 
 int add_excludes_from_file_to_list(const char *fname,

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