Per C11 6.10.3.4/3, _Pragma operators are handled during rescan of an expanded macro body. Therefore, this should work:

  #define true \
    _Pragma("clang diagnostic push") \
    _Pragma("clang diagnostic ignored \"-Wdisabled-macro-expansion\"") \
    true \
    _Pragma("clang diagnostic pop")

  #define CAT2(x,y) x##y
  #define CAT(x,y) CAT2(x,y)
  int untrue = 0;
  int x = CAT(un, true);

... because the pragma should take effect during the rescan of the
expansion of 'true', and per 6.10.9/1 the tokens should be removed before we perform the token paste.


This should give 'const char *p = "xyzzy";' and no warning.

  #define foo _Pragma("GCC diagnostic ignored \"-Wuninitialized\"") xyzzy
  #define str(x) #x
  #define STR(x) str(x)
  const char *p = STR(foo);
  int n() { int k; return k; }

Clang gets both of these wrong.