When -fdiagnostics-print-source-range-info is specified,

print the diagnostic category number in the [] at the end
of the line.  For example:

$ cat t.c 
#include <stdio.h>
void foo() {
 printf("%s", 4);
}
$  clang t.c -fsyntax-only -fdiagnostics-print-source-range-info
t.c:3:11:{3:10-3:12}{3:15-3:16}: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat,1]
  printf("%s", 4);
          ~^   ~
1 warning generated.

Clients that want category information can now pick the number 
out of the output, rdar://7928231.

More coming.

llvm-svn: 103053