color: allow "no-" for negating attributes

Using "no-bold" rather than "nobold" is easier to read and
more natural to type (to me, anyway, even though I was the
person who introduced "nobold" in the first place). It's
easy to allow both.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -163,7 +163,7 @@ hex, like `#ff0ab3`.
 The accepted attributes are `bold`, `dim`, `ul`, `blink`, and `reverse`.
 The position of any attributes with respect to the colors (before, after,
 or in between), doesn't matter. Specific attributes may be turned off
-by prefixing them with `no` (e.g., `noreverse`, `noul`, etc).
+by prefixing them with `no` or `no-` (e.g., `noreverse`, `no-ul`, etc).
 +
 For git's pre-defined color slots, the attributes are meant to be reset
 at the beginning of each item in the colored output. So setting

color.c

@@ -141,8 +141,10 @@ static int parse_attr(const char *name, size_t len)
 	int negate = 0;
 	int i;
 
-	if (skip_prefix_mem(name, len, "no", &name, &len))
+	if (skip_prefix_mem(name, len, "no", &name, &len)) {
+		skip_prefix_mem(name, len, "-", &name, &len);
 		negate = 1;
+	}
 
 	for (i = 0; i < ARRAY_SIZE(attrs); i++) {
 		if (attrs[i].len == len && !memcmp(attrs[i].name, name, len))

t/t4026-color.sh

@@ -50,6 +50,10 @@ test_expect_success 'attr negation' '
 	color "nobold nodim noul noblink noreverse" "[22;24;25;27m"
 '
 
+test_expect_success '"no-" variant of negation' '
+	color "no-bold no-blink" "[22;25m"
+'
+
 test_expect_success 'long color specification' '
 	color "254 255 bold dim ul blink reverse" "[1;2;4;5;7;38;5;254;48;5;255m"
 '