Fix "diff --check" whitespace detection

"diff --check" would only detect spaces before tabs if a tab was the
last character in the leading indent. Fix that and add a test case to
make sure the bug doesn't regress in the future.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -1044,11 +1044,18 @@ static void checkdiff_consume(void *priv, char *line, unsigned long len)
 		int i, spaces = 0, space_before_tab = 0, white_space_at_end = 0;
 
 		/* check space before tab */
-		for (i = 1; i < len && (line[i] == ' ' || line[i] == '\t'); i++)
+		for (i = 1; i < len; i++) {
 			if (line[i] == ' ')
 				spaces++;
-		if (line[i - 1] == '\t' && spaces)
-			space_before_tab = 1;
+			else if (line[i] == '\t') {
+				if (spaces) {
+					space_before_tab = 1;
+					break;
+				}
+			}
+			else
+				break;
+		}
 
 		/* check whitespace at line end */
 		if (line[len - 1] == '\n')

t/t4015-diff-whitespace.sh

@@ -117,4 +117,13 @@ EOF
 git diff -b > out
 test_expect_success 'another test, with -b' 'git diff expect out'
 
+
+test_expect_success 'check mixed spaces and tabs in indent' '
+
+	# This is indented with SP HT SP.
+	echo " 	 foo();" > x &&
+	git diff --check | grep "space before tab"
+
+'
+
 test_done