refactor(printf) add printf-like function attribute to _lv_txt_set_text_vfmt and lv_label_set_text_fmt (#2332)

This improves static analysis and compiler warnings of incorrect format usage.

src/misc/lv_txt.c

@@ -483,7 +483,7 @@ void _lv_txt_cut(char * txt, uint32_t pos, uint32_t len)
  * @param fmt `printf`-like format
  * @return pointer to the allocated text string.
  */
-char * _lv_txt_set_text_vfmt(const char * fmt, va_list ap)
+LV_FORMAT_ATTRIBUTE(1, 0) char * _lv_txt_set_text_vfmt(const char * fmt, va_list ap)
 {
     /*Allocate space for the new text by using trick from C99 standard section 7.19.6.12*/
     va_list ap_copy;

src/misc/lv_txt.h

@@ -20,6 +20,7 @@ extern "C" {
 #include "lv_area.h"
 #include "../font/lv_font.h"
 #include "lv_printf.h"
+#include "lv_types.h"
 
 /*********************
  *      DEFINES
@@ -141,7 +142,7 @@ void _lv_txt_cut(char * txt, uint32_t pos, uint32_t len);
  * @param fmt `printf`-like format
  * @return pointer to the allocated text string.
  */
-char * _lv_txt_set_text_vfmt(const char * fmt, va_list ap);
+char * _lv_txt_set_text_vfmt(const char * fmt, va_list ap) LV_FORMAT_ATTRIBUTE(1, 0);
 
 /**
  * Decode two encoded character from a string.

src/misc/lv_types.h

@@ -80,6 +80,12 @@ typedef uint32_t lv_uintptr_t;
 #define _LV_CONCAT3(x, y, z) x ## y ## z
 #define LV_CONCAT3(x, y, z) _LV_CONCAT3(x, y, z)
 
+#if defined(__clang__) || defined(__GNUC__) || defined(__GNUG__)
+#define LV_FORMAT_ATTRIBUTE(fmtstr, vararg) __attribute__ ((format(printf, fmtstr, vararg)))
+#else
+#define LV_FORMAT_ATTRIBUTE(fmtstr, vararg)
+#endif
+
 #ifdef __cplusplus
 } /*extern "C"*/
 #endif

src/widgets/lv_label.c

@@ -1,4 +1,4 @@
-/**
+/**
  * @file lv_label.c
  *
  */
@@ -144,7 +144,7 @@ void lv_label_set_text(lv_obj_t * obj, const char * text)
     lv_label_refr_text(obj);
 }
 
-void lv_label_set_text_fmt(lv_obj_t * obj, const char * fmt, ...)
+LV_FORMAT_ATTRIBUTE(2, 3) void lv_label_set_text_fmt(lv_obj_t * obj, const char * fmt, ...)
 {
     LV_ASSERT_OBJ(obj, MY_CLASS);
     LV_ASSERT_NULL(fmt);

src/widgets/lv_label.h

@@ -105,7 +105,7 @@ void lv_label_set_text(lv_obj_t * obj, const char * text);
  * @param fmt           `printf`-like format
  * @example lv_label_set_text_fmt(label1, "%d user", user_num);
  */
-void lv_label_set_text_fmt(lv_obj_t * obj, const char * fmt, ...);
+void lv_label_set_text_fmt(lv_obj_t * obj, const char * fmt, ...) LV_FORMAT_ATTRIBUTE(2, 3);
 
 /**
  * Set a static text. It will not be saved by the label so the 'text' variable