t-ctype: allow NUL anywhere in the specification string

Replace the custom function is_in() for looking up a character in the
specification string with memchr(3) and sizeof.  This is shorter,
simpler and allows NUL anywhere in the string, which may come in handy
if we ever want to support more character classes that contain it.

Getting the string size using sizeof only works in a macro and with a
string constant.  Use ARRAY_SIZE and compile-time checks to make sure we
are not passed a string pointer.

Signed-off-by: René Scharfe <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: rscharfe

t/unit-tests/t-ctype.c

@@ -1,23 +1,13 @@
 #include "test-lib.h"
 
-static int is_in(const char *s, int ch)
-{
-	/*
-	 * We can't find NUL using strchr. Accept it as the first
-	 * character in the spec -- there are no empty classes.
-	 */
-	if (ch == '\0')
-		return ch == *s;
-	if (*s == '\0')
-		s++;
-	return !!strchr(s, ch);
-}
-
 /* Macro to test a character type */
 #define TEST_CTYPE_FUNC(func, string) \
 static void test_ctype_##func(void) { \
+	size_t len = ARRAY_SIZE(string) - 1 + \
+		BUILD_ASSERT_OR_ZERO(ARRAY_SIZE(string) > 0) + \
+		BUILD_ASSERT_OR_ZERO(sizeof(string[0]) == sizeof(char)); \
 	for (int i = 0; i < 256; i++) { \
-		if (!check_int(func(i), ==, is_in(string, i))) \
+		if (!check_int(func(i), ==, !!memchr(string, i, len))) \
 			test_msg("       i: 0x%02x", i); \
 	} \
 	if (!check(!func(EOF))) \