blame: reject empty ranges -L,+0 and -L,-0

Empty ranges -L,+0 and -L,-0 are nonsensical in the context of blame yet
they are accepted (in fact, both are interpreted as -L1,Y where Y is
end-of-file). Report them as invalid.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

line-range.c

@@ -21,7 +21,7 @@ static const char *parse_loc(const char *spec, nth_line_fn_t nth_line,
 	 * for 20 lines, or "-L <something>,-5" for 5 lines ending at
 	 * <something>.
 	 */
-	if (1 < begin && (spec[0] == '+' || spec[0] == '-')) {
+	if (1 <= begin && (spec[0] == '+' || spec[0] == '-')) {
 		num = strtol(spec + 1, &term, 10);
 		if (term != spec + 1) {
 			if (!ret)

t/annotate-tests.sh

@@ -185,7 +185,7 @@ test_expect_success 'blame -L Y,X (undocumented)' '
 	check_count -L6,3 B 1 B1 1 B2 1 D 1
 '
 
-test_expect_failure 'blame -L ,+0' '
+test_expect_success 'blame -L ,+0' '
 	test_must_fail $PROG -L,+0 file
 '
 
@@ -201,7 +201,7 @@ test_expect_success 'blame -L X,+N' '
 	check_count -L3,+4 B 1 B1 1 B2 1 D 1
 '
 
-test_expect_failure 'blame -L ,-0' '
+test_expect_success 'blame -L ,-0' '
 	test_must_fail $PROG -L,-0 file
 '