[PATCH 3/3] wt-status: use "format" function attribute for status_printf

[Jeff King <peff@peff.net>]

These functions could benefit from the added compile-time
safety of having the compiler check printf arguments.

Unfortunately, we also sometimes pass an empty format string,
which will cause false positives with -Wformat-zero-length.
In this case, that warning is wrong because our function is
not a no-op with an empty format: it may be printing
colorized output along with a trailing newline.

Signed-off-by: Jeff King <peff@peff.net>
---
I'm torn on this one. It really does provide us with more compile-time
safety checks, but it's annoying that "-Wall -Werror" will no longer
work out of the box.

We could also add a status_printf_empty_line() function, but that feels
like a bit of a hack. Searching online, I also found the amusing
suggestion to do:

  status_printf_ln(s, color, "%.*s", 0,
                   "-Wformat-zero-length please choke on a bucket of socks");

but I think that is probably worse than adding a specialized function.

 wt-status.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/wt-status.h b/wt-status.h
index 4121bc2..fb7152e 100644
--- a/wt-status.h
+++ b/wt-status.h
@@ -96,9 +96,9 @@ void wt_porcelain_print(struct wt_status *s);
 void wt_shortstatus_print(struct wt_status *s);
 void wt_porcelain_print(struct wt_status *s);
 
-void status_printf_ln(struct wt_status *s, const char *color, const char *fmt, ...)
-	;
-void status_printf(struct wt_status *s, const char *color, const char *fmt, ...)
-	;
+__attribute__((format (printf, 3, 4)))
+void status_printf_ln(struct wt_status *s, const char *color, const char *fmt, ...);
+__attribute__((format (printf, 3, 4)))
+void status_printf(struct wt_status *s, const char *color, const char *fmt, ...);
 
 #endif /* STATUS_H */
-- 
1.8.3.rc3.24.gec82cb9