[Bug c/85949] New: __attribute__ ((format (printf,1,1))); improve error messages

["jg at jguk dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85949

            Bug ID: 85949
           Summary: __attribute__ ((format (printf,1,1)));  improve error
                    messages
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jg at jguk dot org
  Target Milestone: ---

Created attachment 44195
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44195&action=edit
main

Hello

This is very useful!

Could the build errors be clearer?

I found this online which describes the parameter order

https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html#Attribute-Syntax

Also, could the carat be accurate on the output, it is stuck at char 1.

I included two examples (2,3) and (1,1) below
It would actually require (1,2) to compile.

Output:

~$ gcc -o main main.c -Wall -Werror -Wconversion
main.c:7:1: error: format string argument is not a string type
 void str_fmt(const char * const format, ...) __attribute__ ((format
(printf,2,3)));
 ^
jonny@asus:~$ gcc -o main main.c -Wall -Werror -Wconversion
main.c:7:1: error: format string argument follows the args to be formatted
 void str_fmt(const char * const format, ...) __attribute__ ((format
(printf,1,1)));
 ^


Expected:

jonny@asus:~$ gcc -o main main.c -Wall -Werror -Wconversion
main.c:7:1: error: format string argument variadic list follows the args to be
formatted
 void str_fmt(const char * const format, ...) __attribute__ ((format
(printf,1,1)));
                                                                             ^

~$ gcc -o main main.c -Wall -Werror -Wconversion
main.c:7:78: error: format string argument ‘2’ is not a string type
 void str_fmt(const char * const format, ...) __attribute__ ((format
(printf,2,3)));
                                                                             ^
main.c:7:80: error: format string argument ‘3’ is not present
 void str_fmt(const char * const format, ...) __attribute__ ((format
(printf,2,3)));
                                                                              
^