Fix variadic forwarding in sway_assert

_sway_assert is a variadic function which tries
to delegate to another variadic function. This
requires a vprintf-style variant of the delegate.

https://stackoverflow.com/a/150616

common/log.c

@@ -63,7 +63,8 @@ void sway_abort(const char *format, ...) {
 	sway_terminate(EXIT_FAILURE);
 }
 
-void _sway_log(const char *filename, int line, log_importance_t verbosity, const char* format, ...) {
+void _sway_vlog(const char *filename, int line, log_importance_t verbosity,
+		const char *format, va_list args) {
 	if (verbosity <= v) {
 		// prefix the time to the log message
 		static struct tm result;
@@ -99,10 +100,7 @@ void _sway_log(const char *filename, int line, log_importance_t verbosity, const
 			fprintf(stderr, "[%s:%d] ", file, line);
 		}
 
-		va_list args;
-		va_start(args, format);
 		vfprintf(stderr, format, args);
-		va_end(args);
 
 		if (colored && isatty(STDERR_FILENO)) {
 			fprintf(stderr, "\x1B[0m");
@@ -111,6 +109,13 @@ void _sway_log(const char *filename, int line, log_importance_t verbosity, const
 	}
 }
 
+void _sway_log(const char *filename, int line, log_importance_t verbosity, const char* format, ...) {
+	va_list args;
+	va_start(args, format);
+	_sway_vlog(filename, line, verbosity, format, args);
+	va_end(args);
+}
+
 void sway_log_errno(log_importance_t verbosity, char* format, ...) {
 	if (verbosity <= v) {
 		unsigned int c = verbosity;
@@ -144,7 +149,7 @@ bool _sway_assert(bool condition, const char* format, ...) {
 
 	va_list args;
 	va_start(args, format);
-	sway_log(L_ERROR, format, args);
+	sway_vlog(L_ERROR, format, args);
 	va_end(args);
 
 #ifndef NDEBUG

include/log.h

@@ -28,6 +28,9 @@ void _sway_log(const char *filename, int line, log_importance_t verbosity, const
 #define sway_log(VERBOSITY, FMT, ...) \
 	_sway_log(__FILE__, __LINE__, VERBOSITY, FMT, ##__VA_ARGS__)
 
+#define sway_vlog(VERBOSITY, FMT, VA_ARGS) \
+    _sway_vlog(__FILE__, __LINE__, VERBOSITY, FMT, VA_ARGS)
+
 void error_handler(int sig);
 
 #endif