test: promote the win32-repairing systemf wrapper to all systemf calls

tar/test/test_option_mtime.c

@@ -6,23 +6,6 @@
  */
 #include "test.h"
 
-#if defined(_WIN32) && !defined(__CYGWIN__)
-/* system() on Windows runs its arguments through CMD.EXE, which has
- * notoriously unfriendly quoting rules. The current best documented way around
- * them is to wrap your *entire commandline* in sacrificial quotes.
- *
- * See CMD.EXE /? for more information. Excerpted here:
- * | Otherwise, old behavior is to see if the first character is
- * | a quote character and if so, strip the leading character and
- * | remove the last quote character on the command line, preserving
- * | any text after the last quote character.
- *
- * Since this test makes heavy use of systemf() with quoted arguments inside
- * the commandline, this macro is unfortunately an easier workaround.
- */
-#define systemf(command, ...) systemf("\"" command "\"", __VA_ARGS__)
-#endif
-
 DEFINE_TEST(test_option_mtime)
 {
 	/* Create three files with different mtimes. */

test_utils/test_main.c

@@ -3056,11 +3056,41 @@ systemf(const char *fmt, ...)
 	pid_t pid;
 #endif
 	va_list ap;
+	size_t off = 0, avail = sizeof(buff);
 	int r;
 
+#if defined(_WIN32) && !defined(__CYGWIN__)
+	/* system() on Windows runs its arguments through CMD.EXE, which has
+	 * notoriously unfriendly quoting rules. The current best documented way around
+	 * them is to wrap your *entire commandline* in sacrificial quotes.
+	 *
+	 * See CMD.EXE /? for more information. Excerpted here:
+	 * | Otherwise, old behavior is to see if the first character is
+	 * | a quote character and if so, strip the leading character and
+	 * | remove the last quote character on the command line, preserving
+	 * | any text after the last quote character.
+	 *
+	 * Since these tests often make use of systemf() with quoted arguments inside
+	 * the commandline, wrap every formatted commandline in quotes.
+	 */
+	avail -= 2;
+	off++;
+	buff[0] = '"';
+#endif
+
 	va_start(ap, fmt);
-	vsnprintf(buff, sizeof(buff), fmt, ap);
+	r = vsnprintf(buff + off, avail, fmt, ap);
 	va_end(ap);
+
+	if (r < 0 || (size_t)r > avail) {
+		return (-1);
+	}
+
+#if defined(_WIN32) && !defined(__CYGWIN__)
+	buff[off + r] = '"';
+	buff[off + r + 1] = '\0';
+#endif
+
 	if (verbosity > VERBOSITY_FULL)
 		logprintf("Cmd: %s\n", buff);
 #if USE_POSIX_SPAWN